2018-02-13 13:13:17 +08:00
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/* SPDX-License-Identifier: GPL-2.0 */
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/* Copyright (C) 2017 Andes Technology Corporation */
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#include <linux/init.h>
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#include <linux/linkage.h>
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#include <asm/asm.h>
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#include <asm/csr.h>
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#include <asm/unistd.h>
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#include <asm/thread_info.h>
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#include <asm/asm-offsets.h>
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#include <asm-generic/export.h>
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#include <asm/ftrace.h>
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.text
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riscv: ftrace: Reduce the detour code size to half
Use a temporary register to reduce the size of detour code from 16 bytes to
8 bytes. The previous implementation is from 'commit afc76b8b8011 ("riscv:
Using PATCHABLE_FUNCTION_ENTRY instead of MCOUNT")'.
Before the patch:
<func_prolog>:
0: REG_S ra, -SZREG(sp)
4: auipc ra, ?
8: jalr ?(ra)
12: REG_L ra, -SZREG(sp)
(func_boddy)
After the patch:
<func_prolog>:
0: auipc t0, ?
4: jalr t0, ?(t0)
(func_boddy)
This patch not just reduces the size of detour code, but also fixes an
important issue:
An Ftrace callback registered with FTRACE_OPS_FL_IPMODIFY flag can
actually change the instruction pointer, e.g. to "replace" the given
kernel function with a new one, which is needed for livepatching, etc.
In this case, the trampoline (ftrace_regs_caller) would not return to
<func_prolog+12> but would rather jump to the new function. So, "REG_L
ra, -SZREG(sp)" would not run and the original return address would not
be restored. The kernel is likely to hang or crash as a result.
This can be easily demonstrated if one tries to "replace", say,
cmdline_proc_show() with a new function with the same signature using
instruction_pointer_set(&fregs->regs, new_func_addr) in the Ftrace
callback.
Link: https://lore.kernel.org/linux-riscv/20221122075440.1165172-1-suagrfillet@gmail.com/
Link: https://lore.kernel.org/linux-riscv/d7d5730b-ebef-68e5-5046-e763e1ee6164@yadro.com/
Co-developed-by: Song Shuai <suagrfillet@gmail.com>
Signed-off-by: Song Shuai <suagrfillet@gmail.com>
Signed-off-by: Guo Ren <guoren@linux.alibaba.com>
Signed-off-by: Guo Ren <guoren@kernel.org>
Cc: Evgenii Shatokhin <e.shatokhin@yadro.com>
Reviewed-by: Evgenii Shatokhin <e.shatokhin@yadro.com>
Link: https://lore.kernel.org/r/20230112090603.1295340-4-guoren@kernel.org
Cc: stable@vger.kernel.org
Fixes: 10626c32e382 ("riscv/ftrace: Add basic support")
Signed-off-by: Palmer Dabbelt <palmer@rivosinc.com>
2023-01-12 04:05:59 -05:00
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#define FENTRY_RA_OFFSET 8
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#define ABI_SIZE_ON_STACK 80
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riscv: Using PATCHABLE_FUNCTION_ENTRY instead of MCOUNT
This patch changes the current detour mechanism of dynamic ftrace
which has been discussed during LPC 2020 RISCV-MC [1].
Before the patch, we used mcount for detour:
<funca>:
addi sp,sp,-16
sd ra,8(sp)
sd s0,0(sp)
addi s0,sp,16
mv a5,ra
mv a0,a5
auipc ra,0x0 -> nop
jalr -296(ra) <_mcount@plt> ->nop
...
After the patch, we use nop call site area for detour:
<funca>:
nop -> REG_S ra, -SZREG(sp)
nop -> auipc ra, 0x?
nop -> jalr ?(ra)
nop -> REG_L ra, -SZREG(sp)
...
The mcount mechanism is mixed with gcc function prologue which is
not very clear. The patchable function entry just put 16 bytes nop
before the front of the function prologue which could be filled
with a separated detour mechanism.
[1] https://www.linuxplumbersconf.org/event/7/contributions/807/
Signed-off-by: Guo Ren <guoren@linux.alibaba.com>
Signed-off-by: Palmer Dabbelt <palmerdabbelt@google.com>
2020-12-17 16:01:41 +00:00
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#define ABI_A0 0
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#define ABI_A1 8
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#define ABI_A2 16
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#define ABI_A3 24
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#define ABI_A4 32
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#define ABI_A5 40
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#define ABI_A6 48
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#define ABI_A7 56
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riscv: ftrace: Reduce the detour code size to half
Use a temporary register to reduce the size of detour code from 16 bytes to
8 bytes. The previous implementation is from 'commit afc76b8b8011 ("riscv:
Using PATCHABLE_FUNCTION_ENTRY instead of MCOUNT")'.
Before the patch:
<func_prolog>:
0: REG_S ra, -SZREG(sp)
4: auipc ra, ?
8: jalr ?(ra)
12: REG_L ra, -SZREG(sp)
(func_boddy)
After the patch:
<func_prolog>:
0: auipc t0, ?
4: jalr t0, ?(t0)
(func_boddy)
This patch not just reduces the size of detour code, but also fixes an
important issue:
An Ftrace callback registered with FTRACE_OPS_FL_IPMODIFY flag can
actually change the instruction pointer, e.g. to "replace" the given
kernel function with a new one, which is needed for livepatching, etc.
In this case, the trampoline (ftrace_regs_caller) would not return to
<func_prolog+12> but would rather jump to the new function. So, "REG_L
ra, -SZREG(sp)" would not run and the original return address would not
be restored. The kernel is likely to hang or crash as a result.
This can be easily demonstrated if one tries to "replace", say,
cmdline_proc_show() with a new function with the same signature using
instruction_pointer_set(&fregs->regs, new_func_addr) in the Ftrace
callback.
Link: https://lore.kernel.org/linux-riscv/20221122075440.1165172-1-suagrfillet@gmail.com/
Link: https://lore.kernel.org/linux-riscv/d7d5730b-ebef-68e5-5046-e763e1ee6164@yadro.com/
Co-developed-by: Song Shuai <suagrfillet@gmail.com>
Signed-off-by: Song Shuai <suagrfillet@gmail.com>
Signed-off-by: Guo Ren <guoren@linux.alibaba.com>
Signed-off-by: Guo Ren <guoren@kernel.org>
Cc: Evgenii Shatokhin <e.shatokhin@yadro.com>
Reviewed-by: Evgenii Shatokhin <e.shatokhin@yadro.com>
Link: https://lore.kernel.org/r/20230112090603.1295340-4-guoren@kernel.org
Cc: stable@vger.kernel.org
Fixes: 10626c32e382 ("riscv/ftrace: Add basic support")
Signed-off-by: Palmer Dabbelt <palmer@rivosinc.com>
2023-01-12 04:05:59 -05:00
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#define ABI_T0 64
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#define ABI_RA 72
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riscv: Using PATCHABLE_FUNCTION_ENTRY instead of MCOUNT
This patch changes the current detour mechanism of dynamic ftrace
which has been discussed during LPC 2020 RISCV-MC [1].
Before the patch, we used mcount for detour:
<funca>:
addi sp,sp,-16
sd ra,8(sp)
sd s0,0(sp)
addi s0,sp,16
mv a5,ra
mv a0,a5
auipc ra,0x0 -> nop
jalr -296(ra) <_mcount@plt> ->nop
...
After the patch, we use nop call site area for detour:
<funca>:
nop -> REG_S ra, -SZREG(sp)
nop -> auipc ra, 0x?
nop -> jalr ?(ra)
nop -> REG_L ra, -SZREG(sp)
...
The mcount mechanism is mixed with gcc function prologue which is
not very clear. The patchable function entry just put 16 bytes nop
before the front of the function prologue which could be filled
with a separated detour mechanism.
[1] https://www.linuxplumbersconf.org/event/7/contributions/807/
Signed-off-by: Guo Ren <guoren@linux.alibaba.com>
Signed-off-by: Palmer Dabbelt <palmerdabbelt@google.com>
2020-12-17 16:01:41 +00:00
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.macro SAVE_ABI
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addi sp, sp, -ABI_SIZE_ON_STACK
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REG_S a0, ABI_A0(sp)
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REG_S a1, ABI_A1(sp)
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REG_S a2, ABI_A2(sp)
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REG_S a3, ABI_A3(sp)
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REG_S a4, ABI_A4(sp)
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REG_S a5, ABI_A5(sp)
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REG_S a6, ABI_A6(sp)
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REG_S a7, ABI_A7(sp)
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riscv: ftrace: Reduce the detour code size to half
Use a temporary register to reduce the size of detour code from 16 bytes to
8 bytes. The previous implementation is from 'commit afc76b8b8011 ("riscv:
Using PATCHABLE_FUNCTION_ENTRY instead of MCOUNT")'.
Before the patch:
<func_prolog>:
0: REG_S ra, -SZREG(sp)
4: auipc ra, ?
8: jalr ?(ra)
12: REG_L ra, -SZREG(sp)
(func_boddy)
After the patch:
<func_prolog>:
0: auipc t0, ?
4: jalr t0, ?(t0)
(func_boddy)
This patch not just reduces the size of detour code, but also fixes an
important issue:
An Ftrace callback registered with FTRACE_OPS_FL_IPMODIFY flag can
actually change the instruction pointer, e.g. to "replace" the given
kernel function with a new one, which is needed for livepatching, etc.
In this case, the trampoline (ftrace_regs_caller) would not return to
<func_prolog+12> but would rather jump to the new function. So, "REG_L
ra, -SZREG(sp)" would not run and the original return address would not
be restored. The kernel is likely to hang or crash as a result.
This can be easily demonstrated if one tries to "replace", say,
cmdline_proc_show() with a new function with the same signature using
instruction_pointer_set(&fregs->regs, new_func_addr) in the Ftrace
callback.
Link: https://lore.kernel.org/linux-riscv/20221122075440.1165172-1-suagrfillet@gmail.com/
Link: https://lore.kernel.org/linux-riscv/d7d5730b-ebef-68e5-5046-e763e1ee6164@yadro.com/
Co-developed-by: Song Shuai <suagrfillet@gmail.com>
Signed-off-by: Song Shuai <suagrfillet@gmail.com>
Signed-off-by: Guo Ren <guoren@linux.alibaba.com>
Signed-off-by: Guo Ren <guoren@kernel.org>
Cc: Evgenii Shatokhin <e.shatokhin@yadro.com>
Reviewed-by: Evgenii Shatokhin <e.shatokhin@yadro.com>
Link: https://lore.kernel.org/r/20230112090603.1295340-4-guoren@kernel.org
Cc: stable@vger.kernel.org
Fixes: 10626c32e382 ("riscv/ftrace: Add basic support")
Signed-off-by: Palmer Dabbelt <palmer@rivosinc.com>
2023-01-12 04:05:59 -05:00
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REG_S t0, ABI_T0(sp)
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riscv: Using PATCHABLE_FUNCTION_ENTRY instead of MCOUNT
This patch changes the current detour mechanism of dynamic ftrace
which has been discussed during LPC 2020 RISCV-MC [1].
Before the patch, we used mcount for detour:
<funca>:
addi sp,sp,-16
sd ra,8(sp)
sd s0,0(sp)
addi s0,sp,16
mv a5,ra
mv a0,a5
auipc ra,0x0 -> nop
jalr -296(ra) <_mcount@plt> ->nop
...
After the patch, we use nop call site area for detour:
<funca>:
nop -> REG_S ra, -SZREG(sp)
nop -> auipc ra, 0x?
nop -> jalr ?(ra)
nop -> REG_L ra, -SZREG(sp)
...
The mcount mechanism is mixed with gcc function prologue which is
not very clear. The patchable function entry just put 16 bytes nop
before the front of the function prologue which could be filled
with a separated detour mechanism.
[1] https://www.linuxplumbersconf.org/event/7/contributions/807/
Signed-off-by: Guo Ren <guoren@linux.alibaba.com>
Signed-off-by: Palmer Dabbelt <palmerdabbelt@google.com>
2020-12-17 16:01:41 +00:00
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REG_S ra, ABI_RA(sp)
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2018-02-13 13:13:17 +08:00
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.endm
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riscv: Using PATCHABLE_FUNCTION_ENTRY instead of MCOUNT
This patch changes the current detour mechanism of dynamic ftrace
which has been discussed during LPC 2020 RISCV-MC [1].
Before the patch, we used mcount for detour:
<funca>:
addi sp,sp,-16
sd ra,8(sp)
sd s0,0(sp)
addi s0,sp,16
mv a5,ra
mv a0,a5
auipc ra,0x0 -> nop
jalr -296(ra) <_mcount@plt> ->nop
...
After the patch, we use nop call site area for detour:
<funca>:
nop -> REG_S ra, -SZREG(sp)
nop -> auipc ra, 0x?
nop -> jalr ?(ra)
nop -> REG_L ra, -SZREG(sp)
...
The mcount mechanism is mixed with gcc function prologue which is
not very clear. The patchable function entry just put 16 bytes nop
before the front of the function prologue which could be filled
with a separated detour mechanism.
[1] https://www.linuxplumbersconf.org/event/7/contributions/807/
Signed-off-by: Guo Ren <guoren@linux.alibaba.com>
Signed-off-by: Palmer Dabbelt <palmerdabbelt@google.com>
2020-12-17 16:01:41 +00:00
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.macro RESTORE_ABI
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REG_L a0, ABI_A0(sp)
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REG_L a1, ABI_A1(sp)
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REG_L a2, ABI_A2(sp)
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REG_L a3, ABI_A3(sp)
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REG_L a4, ABI_A4(sp)
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REG_L a5, ABI_A5(sp)
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REG_L a6, ABI_A6(sp)
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REG_L a7, ABI_A7(sp)
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riscv: ftrace: Reduce the detour code size to half
Use a temporary register to reduce the size of detour code from 16 bytes to
8 bytes. The previous implementation is from 'commit afc76b8b8011 ("riscv:
Using PATCHABLE_FUNCTION_ENTRY instead of MCOUNT")'.
Before the patch:
<func_prolog>:
0: REG_S ra, -SZREG(sp)
4: auipc ra, ?
8: jalr ?(ra)
12: REG_L ra, -SZREG(sp)
(func_boddy)
After the patch:
<func_prolog>:
0: auipc t0, ?
4: jalr t0, ?(t0)
(func_boddy)
This patch not just reduces the size of detour code, but also fixes an
important issue:
An Ftrace callback registered with FTRACE_OPS_FL_IPMODIFY flag can
actually change the instruction pointer, e.g. to "replace" the given
kernel function with a new one, which is needed for livepatching, etc.
In this case, the trampoline (ftrace_regs_caller) would not return to
<func_prolog+12> but would rather jump to the new function. So, "REG_L
ra, -SZREG(sp)" would not run and the original return address would not
be restored. The kernel is likely to hang or crash as a result.
This can be easily demonstrated if one tries to "replace", say,
cmdline_proc_show() with a new function with the same signature using
instruction_pointer_set(&fregs->regs, new_func_addr) in the Ftrace
callback.
Link: https://lore.kernel.org/linux-riscv/20221122075440.1165172-1-suagrfillet@gmail.com/
Link: https://lore.kernel.org/linux-riscv/d7d5730b-ebef-68e5-5046-e763e1ee6164@yadro.com/
Co-developed-by: Song Shuai <suagrfillet@gmail.com>
Signed-off-by: Song Shuai <suagrfillet@gmail.com>
Signed-off-by: Guo Ren <guoren@linux.alibaba.com>
Signed-off-by: Guo Ren <guoren@kernel.org>
Cc: Evgenii Shatokhin <e.shatokhin@yadro.com>
Reviewed-by: Evgenii Shatokhin <e.shatokhin@yadro.com>
Link: https://lore.kernel.org/r/20230112090603.1295340-4-guoren@kernel.org
Cc: stable@vger.kernel.org
Fixes: 10626c32e382 ("riscv/ftrace: Add basic support")
Signed-off-by: Palmer Dabbelt <palmer@rivosinc.com>
2023-01-12 04:05:59 -05:00
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REG_L t0, ABI_T0(sp)
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riscv: Using PATCHABLE_FUNCTION_ENTRY instead of MCOUNT
This patch changes the current detour mechanism of dynamic ftrace
which has been discussed during LPC 2020 RISCV-MC [1].
Before the patch, we used mcount for detour:
<funca>:
addi sp,sp,-16
sd ra,8(sp)
sd s0,0(sp)
addi s0,sp,16
mv a5,ra
mv a0,a5
auipc ra,0x0 -> nop
jalr -296(ra) <_mcount@plt> ->nop
...
After the patch, we use nop call site area for detour:
<funca>:
nop -> REG_S ra, -SZREG(sp)
nop -> auipc ra, 0x?
nop -> jalr ?(ra)
nop -> REG_L ra, -SZREG(sp)
...
The mcount mechanism is mixed with gcc function prologue which is
not very clear. The patchable function entry just put 16 bytes nop
before the front of the function prologue which could be filled
with a separated detour mechanism.
[1] https://www.linuxplumbersconf.org/event/7/contributions/807/
Signed-off-by: Guo Ren <guoren@linux.alibaba.com>
Signed-off-by: Palmer Dabbelt <palmerdabbelt@google.com>
2020-12-17 16:01:41 +00:00
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REG_L ra, ABI_RA(sp)
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addi sp, sp, ABI_SIZE_ON_STACK
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2018-02-13 13:13:17 +08:00
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.endm
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|
riscv: Using PATCHABLE_FUNCTION_ENTRY instead of MCOUNT
This patch changes the current detour mechanism of dynamic ftrace
which has been discussed during LPC 2020 RISCV-MC [1].
Before the patch, we used mcount for detour:
<funca>:
addi sp,sp,-16
sd ra,8(sp)
sd s0,0(sp)
addi s0,sp,16
mv a5,ra
mv a0,a5
auipc ra,0x0 -> nop
jalr -296(ra) <_mcount@plt> ->nop
...
After the patch, we use nop call site area for detour:
<funca>:
nop -> REG_S ra, -SZREG(sp)
nop -> auipc ra, 0x?
nop -> jalr ?(ra)
nop -> REG_L ra, -SZREG(sp)
...
The mcount mechanism is mixed with gcc function prologue which is
not very clear. The patchable function entry just put 16 bytes nop
before the front of the function prologue which could be filled
with a separated detour mechanism.
[1] https://www.linuxplumbersconf.org/event/7/contributions/807/
Signed-off-by: Guo Ren <guoren@linux.alibaba.com>
Signed-off-by: Palmer Dabbelt <palmerdabbelt@google.com>
2020-12-17 16:01:41 +00:00
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#ifdef CONFIG_DYNAMIC_FTRACE_WITH_REGS
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.macro SAVE_ALL
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addi sp, sp, -PT_SIZE_ON_STACK
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riscv: ftrace: Reduce the detour code size to half
Use a temporary register to reduce the size of detour code from 16 bytes to
8 bytes. The previous implementation is from 'commit afc76b8b8011 ("riscv:
Using PATCHABLE_FUNCTION_ENTRY instead of MCOUNT")'.
Before the patch:
<func_prolog>:
0: REG_S ra, -SZREG(sp)
4: auipc ra, ?
8: jalr ?(ra)
12: REG_L ra, -SZREG(sp)
(func_boddy)
After the patch:
<func_prolog>:
0: auipc t0, ?
4: jalr t0, ?(t0)
(func_boddy)
This patch not just reduces the size of detour code, but also fixes an
important issue:
An Ftrace callback registered with FTRACE_OPS_FL_IPMODIFY flag can
actually change the instruction pointer, e.g. to "replace" the given
kernel function with a new one, which is needed for livepatching, etc.
In this case, the trampoline (ftrace_regs_caller) would not return to
<func_prolog+12> but would rather jump to the new function. So, "REG_L
ra, -SZREG(sp)" would not run and the original return address would not
be restored. The kernel is likely to hang or crash as a result.
This can be easily demonstrated if one tries to "replace", say,
cmdline_proc_show() with a new function with the same signature using
instruction_pointer_set(&fregs->regs, new_func_addr) in the Ftrace
callback.
Link: https://lore.kernel.org/linux-riscv/20221122075440.1165172-1-suagrfillet@gmail.com/
Link: https://lore.kernel.org/linux-riscv/d7d5730b-ebef-68e5-5046-e763e1ee6164@yadro.com/
Co-developed-by: Song Shuai <suagrfillet@gmail.com>
Signed-off-by: Song Shuai <suagrfillet@gmail.com>
Signed-off-by: Guo Ren <guoren@linux.alibaba.com>
Signed-off-by: Guo Ren <guoren@kernel.org>
Cc: Evgenii Shatokhin <e.shatokhin@yadro.com>
Reviewed-by: Evgenii Shatokhin <e.shatokhin@yadro.com>
Link: https://lore.kernel.org/r/20230112090603.1295340-4-guoren@kernel.org
Cc: stable@vger.kernel.org
Fixes: 10626c32e382 ("riscv/ftrace: Add basic support")
Signed-off-by: Palmer Dabbelt <palmer@rivosinc.com>
2023-01-12 04:05:59 -05:00
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REG_S t0, PT_EPC(sp)
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riscv: Using PATCHABLE_FUNCTION_ENTRY instead of MCOUNT
This patch changes the current detour mechanism of dynamic ftrace
which has been discussed during LPC 2020 RISCV-MC [1].
Before the patch, we used mcount for detour:
<funca>:
addi sp,sp,-16
sd ra,8(sp)
sd s0,0(sp)
addi s0,sp,16
mv a5,ra
mv a0,a5
auipc ra,0x0 -> nop
jalr -296(ra) <_mcount@plt> ->nop
...
After the patch, we use nop call site area for detour:
<funca>:
nop -> REG_S ra, -SZREG(sp)
nop -> auipc ra, 0x?
nop -> jalr ?(ra)
nop -> REG_L ra, -SZREG(sp)
...
The mcount mechanism is mixed with gcc function prologue which is
not very clear. The patchable function entry just put 16 bytes nop
before the front of the function prologue which could be filled
with a separated detour mechanism.
[1] https://www.linuxplumbersconf.org/event/7/contributions/807/
Signed-off-by: Guo Ren <guoren@linux.alibaba.com>
Signed-off-by: Palmer Dabbelt <palmerdabbelt@google.com>
2020-12-17 16:01:41 +00:00
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REG_S x1, PT_RA(sp)
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REG_S x2, PT_SP(sp)
|
|
|
|
|
REG_S x3, PT_GP(sp)
|
|
|
|
|
REG_S x4, PT_TP(sp)
|
|
|
|
|
REG_S x5, PT_T0(sp)
|
2023-02-21 22:30:21 -05:00
|
|
|
save_from_x6_to_x31
|
2018-02-13 13:13:18 +08:00
|
|
|
.endm
|
|
|
|
|
|
riscv: Using PATCHABLE_FUNCTION_ENTRY instead of MCOUNT
This patch changes the current detour mechanism of dynamic ftrace
which has been discussed during LPC 2020 RISCV-MC [1].
Before the patch, we used mcount for detour:
<funca>:
addi sp,sp,-16
sd ra,8(sp)
sd s0,0(sp)
addi s0,sp,16
mv a5,ra
mv a0,a5
auipc ra,0x0 -> nop
jalr -296(ra) <_mcount@plt> ->nop
...
After the patch, we use nop call site area for detour:
<funca>:
nop -> REG_S ra, -SZREG(sp)
nop -> auipc ra, 0x?
nop -> jalr ?(ra)
nop -> REG_L ra, -SZREG(sp)
...
The mcount mechanism is mixed with gcc function prologue which is
not very clear. The patchable function entry just put 16 bytes nop
before the front of the function prologue which could be filled
with a separated detour mechanism.
[1] https://www.linuxplumbersconf.org/event/7/contributions/807/
Signed-off-by: Guo Ren <guoren@linux.alibaba.com>
Signed-off-by: Palmer Dabbelt <palmerdabbelt@google.com>
2020-12-17 16:01:41 +00:00
|
|
|
.macro RESTORE_ALL
|
|
|
|
|
REG_L x1, PT_RA(sp)
|
|
|
|
|
REG_L x2, PT_SP(sp)
|
|
|
|
|
REG_L x3, PT_GP(sp)
|
|
|
|
|
REG_L x4, PT_TP(sp)
|
2023-02-21 22:30:21 -05:00
|
|
|
/* Restore t0 with PT_EPC */
|
|
|
|
|
REG_L x5, PT_EPC(sp)
|
|
|
|
|
restore_from_x6_to_x31
|
riscv: Using PATCHABLE_FUNCTION_ENTRY instead of MCOUNT
This patch changes the current detour mechanism of dynamic ftrace
which has been discussed during LPC 2020 RISCV-MC [1].
Before the patch, we used mcount for detour:
<funca>:
addi sp,sp,-16
sd ra,8(sp)
sd s0,0(sp)
addi s0,sp,16
mv a5,ra
mv a0,a5
auipc ra,0x0 -> nop
jalr -296(ra) <_mcount@plt> ->nop
...
After the patch, we use nop call site area for detour:
<funca>:
nop -> REG_S ra, -SZREG(sp)
nop -> auipc ra, 0x?
nop -> jalr ?(ra)
nop -> REG_L ra, -SZREG(sp)
...
The mcount mechanism is mixed with gcc function prologue which is
not very clear. The patchable function entry just put 16 bytes nop
before the front of the function prologue which could be filled
with a separated detour mechanism.
[1] https://www.linuxplumbersconf.org/event/7/contributions/807/
Signed-off-by: Guo Ren <guoren@linux.alibaba.com>
Signed-off-by: Palmer Dabbelt <palmerdabbelt@google.com>
2020-12-17 16:01:41 +00:00
|
|
|
|
|
|
|
|
addi sp, sp, PT_SIZE_ON_STACK
|
|
|
|
|
.endm
|
|
|
|
|
#endif /* CONFIG_DYNAMIC_FTRACE_WITH_REGS */
|
2018-02-13 13:13:18 +08:00
|
|
|
|
2018-02-13 13:13:17 +08:00
|
|
|
ENTRY(ftrace_caller)
|
riscv: Using PATCHABLE_FUNCTION_ENTRY instead of MCOUNT
This patch changes the current detour mechanism of dynamic ftrace
which has been discussed during LPC 2020 RISCV-MC [1].
Before the patch, we used mcount for detour:
<funca>:
addi sp,sp,-16
sd ra,8(sp)
sd s0,0(sp)
addi s0,sp,16
mv a5,ra
mv a0,a5
auipc ra,0x0 -> nop
jalr -296(ra) <_mcount@plt> ->nop
...
After the patch, we use nop call site area for detour:
<funca>:
nop -> REG_S ra, -SZREG(sp)
nop -> auipc ra, 0x?
nop -> jalr ?(ra)
nop -> REG_L ra, -SZREG(sp)
...
The mcount mechanism is mixed with gcc function prologue which is
not very clear. The patchable function entry just put 16 bytes nop
before the front of the function prologue which could be filled
with a separated detour mechanism.
[1] https://www.linuxplumbersconf.org/event/7/contributions/807/
Signed-off-by: Guo Ren <guoren@linux.alibaba.com>
Signed-off-by: Palmer Dabbelt <palmerdabbelt@google.com>
2020-12-17 16:01:41 +00:00
|
|
|
SAVE_ABI
|
2018-02-13 13:13:18 +08:00
|
|
|
|
riscv: ftrace: Reduce the detour code size to half
Use a temporary register to reduce the size of detour code from 16 bytes to
8 bytes. The previous implementation is from 'commit afc76b8b8011 ("riscv:
Using PATCHABLE_FUNCTION_ENTRY instead of MCOUNT")'.
Before the patch:
<func_prolog>:
0: REG_S ra, -SZREG(sp)
4: auipc ra, ?
8: jalr ?(ra)
12: REG_L ra, -SZREG(sp)
(func_boddy)
After the patch:
<func_prolog>:
0: auipc t0, ?
4: jalr t0, ?(t0)
(func_boddy)
This patch not just reduces the size of detour code, but also fixes an
important issue:
An Ftrace callback registered with FTRACE_OPS_FL_IPMODIFY flag can
actually change the instruction pointer, e.g. to "replace" the given
kernel function with a new one, which is needed for livepatching, etc.
In this case, the trampoline (ftrace_regs_caller) would not return to
<func_prolog+12> but would rather jump to the new function. So, "REG_L
ra, -SZREG(sp)" would not run and the original return address would not
be restored. The kernel is likely to hang or crash as a result.
This can be easily demonstrated if one tries to "replace", say,
cmdline_proc_show() with a new function with the same signature using
instruction_pointer_set(&fregs->regs, new_func_addr) in the Ftrace
callback.
Link: https://lore.kernel.org/linux-riscv/20221122075440.1165172-1-suagrfillet@gmail.com/
Link: https://lore.kernel.org/linux-riscv/d7d5730b-ebef-68e5-5046-e763e1ee6164@yadro.com/
Co-developed-by: Song Shuai <suagrfillet@gmail.com>
Signed-off-by: Song Shuai <suagrfillet@gmail.com>
Signed-off-by: Guo Ren <guoren@linux.alibaba.com>
Signed-off-by: Guo Ren <guoren@kernel.org>
Cc: Evgenii Shatokhin <e.shatokhin@yadro.com>
Reviewed-by: Evgenii Shatokhin <e.shatokhin@yadro.com>
Link: https://lore.kernel.org/r/20230112090603.1295340-4-guoren@kernel.org
Cc: stable@vger.kernel.org
Fixes: 10626c32e382 ("riscv/ftrace: Add basic support")
Signed-off-by: Palmer Dabbelt <palmer@rivosinc.com>
2023-01-12 04:05:59 -05:00
|
|
|
addi a0, t0, -FENTRY_RA_OFFSET
|
riscv: Using PATCHABLE_FUNCTION_ENTRY instead of MCOUNT
This patch changes the current detour mechanism of dynamic ftrace
which has been discussed during LPC 2020 RISCV-MC [1].
Before the patch, we used mcount for detour:
<funca>:
addi sp,sp,-16
sd ra,8(sp)
sd s0,0(sp)
addi s0,sp,16
mv a5,ra
mv a0,a5
auipc ra,0x0 -> nop
jalr -296(ra) <_mcount@plt> ->nop
...
After the patch, we use nop call site area for detour:
<funca>:
nop -> REG_S ra, -SZREG(sp)
nop -> auipc ra, 0x?
nop -> jalr ?(ra)
nop -> REG_L ra, -SZREG(sp)
...
The mcount mechanism is mixed with gcc function prologue which is
not very clear. The patchable function entry just put 16 bytes nop
before the front of the function prologue which could be filled
with a separated detour mechanism.
[1] https://www.linuxplumbersconf.org/event/7/contributions/807/
Signed-off-by: Guo Ren <guoren@linux.alibaba.com>
Signed-off-by: Palmer Dabbelt <palmerdabbelt@google.com>
2020-12-17 16:01:41 +00:00
|
|
|
la a1, function_trace_op
|
|
|
|
|
REG_L a2, 0(a1)
|
riscv: ftrace: Reduce the detour code size to half
Use a temporary register to reduce the size of detour code from 16 bytes to
8 bytes. The previous implementation is from 'commit afc76b8b8011 ("riscv:
Using PATCHABLE_FUNCTION_ENTRY instead of MCOUNT")'.
Before the patch:
<func_prolog>:
0: REG_S ra, -SZREG(sp)
4: auipc ra, ?
8: jalr ?(ra)
12: REG_L ra, -SZREG(sp)
(func_boddy)
After the patch:
<func_prolog>:
0: auipc t0, ?
4: jalr t0, ?(t0)
(func_boddy)
This patch not just reduces the size of detour code, but also fixes an
important issue:
An Ftrace callback registered with FTRACE_OPS_FL_IPMODIFY flag can
actually change the instruction pointer, e.g. to "replace" the given
kernel function with a new one, which is needed for livepatching, etc.
In this case, the trampoline (ftrace_regs_caller) would not return to
<func_prolog+12> but would rather jump to the new function. So, "REG_L
ra, -SZREG(sp)" would not run and the original return address would not
be restored. The kernel is likely to hang or crash as a result.
This can be easily demonstrated if one tries to "replace", say,
cmdline_proc_show() with a new function with the same signature using
instruction_pointer_set(&fregs->regs, new_func_addr) in the Ftrace
callback.
Link: https://lore.kernel.org/linux-riscv/20221122075440.1165172-1-suagrfillet@gmail.com/
Link: https://lore.kernel.org/linux-riscv/d7d5730b-ebef-68e5-5046-e763e1ee6164@yadro.com/
Co-developed-by: Song Shuai <suagrfillet@gmail.com>
Signed-off-by: Song Shuai <suagrfillet@gmail.com>
Signed-off-by: Guo Ren <guoren@linux.alibaba.com>
Signed-off-by: Guo Ren <guoren@kernel.org>
Cc: Evgenii Shatokhin <e.shatokhin@yadro.com>
Reviewed-by: Evgenii Shatokhin <e.shatokhin@yadro.com>
Link: https://lore.kernel.org/r/20230112090603.1295340-4-guoren@kernel.org
Cc: stable@vger.kernel.org
Fixes: 10626c32e382 ("riscv/ftrace: Add basic support")
Signed-off-by: Palmer Dabbelt <palmer@rivosinc.com>
2023-01-12 04:05:59 -05:00
|
|
|
mv a1, ra
|
riscv: Using PATCHABLE_FUNCTION_ENTRY instead of MCOUNT
This patch changes the current detour mechanism of dynamic ftrace
which has been discussed during LPC 2020 RISCV-MC [1].
Before the patch, we used mcount for detour:
<funca>:
addi sp,sp,-16
sd ra,8(sp)
sd s0,0(sp)
addi s0,sp,16
mv a5,ra
mv a0,a5
auipc ra,0x0 -> nop
jalr -296(ra) <_mcount@plt> ->nop
...
After the patch, we use nop call site area for detour:
<funca>:
nop -> REG_S ra, -SZREG(sp)
nop -> auipc ra, 0x?
nop -> jalr ?(ra)
nop -> REG_L ra, -SZREG(sp)
...
The mcount mechanism is mixed with gcc function prologue which is
not very clear. The patchable function entry just put 16 bytes nop
before the front of the function prologue which could be filled
with a separated detour mechanism.
[1] https://www.linuxplumbersconf.org/event/7/contributions/807/
Signed-off-by: Guo Ren <guoren@linux.alibaba.com>
Signed-off-by: Palmer Dabbelt <palmerdabbelt@google.com>
2020-12-17 16:01:41 +00:00
|
|
|
mv a3, sp
|
2018-02-13 13:13:18 +08:00
|
|
|
|
2018-02-13 13:13:17 +08:00
|
|
|
ftrace_call:
|
|
|
|
|
.global ftrace_call
|
|
|
|
|
call ftrace_stub
|
2018-02-13 13:13:18 +08:00
|
|
|
|
|
|
|
|
#ifdef CONFIG_FUNCTION_GRAPH_TRACER
|
riscv: ftrace: Reduce the detour code size to half
Use a temporary register to reduce the size of detour code from 16 bytes to
8 bytes. The previous implementation is from 'commit afc76b8b8011 ("riscv:
Using PATCHABLE_FUNCTION_ENTRY instead of MCOUNT")'.
Before the patch:
<func_prolog>:
0: REG_S ra, -SZREG(sp)
4: auipc ra, ?
8: jalr ?(ra)
12: REG_L ra, -SZREG(sp)
(func_boddy)
After the patch:
<func_prolog>:
0: auipc t0, ?
4: jalr t0, ?(t0)
(func_boddy)
This patch not just reduces the size of detour code, but also fixes an
important issue:
An Ftrace callback registered with FTRACE_OPS_FL_IPMODIFY flag can
actually change the instruction pointer, e.g. to "replace" the given
kernel function with a new one, which is needed for livepatching, etc.
In this case, the trampoline (ftrace_regs_caller) would not return to
<func_prolog+12> but would rather jump to the new function. So, "REG_L
ra, -SZREG(sp)" would not run and the original return address would not
be restored. The kernel is likely to hang or crash as a result.
This can be easily demonstrated if one tries to "replace", say,
cmdline_proc_show() with a new function with the same signature using
instruction_pointer_set(&fregs->regs, new_func_addr) in the Ftrace
callback.
Link: https://lore.kernel.org/linux-riscv/20221122075440.1165172-1-suagrfillet@gmail.com/
Link: https://lore.kernel.org/linux-riscv/d7d5730b-ebef-68e5-5046-e763e1ee6164@yadro.com/
Co-developed-by: Song Shuai <suagrfillet@gmail.com>
Signed-off-by: Song Shuai <suagrfillet@gmail.com>
Signed-off-by: Guo Ren <guoren@linux.alibaba.com>
Signed-off-by: Guo Ren <guoren@kernel.org>
Cc: Evgenii Shatokhin <e.shatokhin@yadro.com>
Reviewed-by: Evgenii Shatokhin <e.shatokhin@yadro.com>
Link: https://lore.kernel.org/r/20230112090603.1295340-4-guoren@kernel.org
Cc: stable@vger.kernel.org
Fixes: 10626c32e382 ("riscv/ftrace: Add basic support")
Signed-off-by: Palmer Dabbelt <palmer@rivosinc.com>
2023-01-12 04:05:59 -05:00
|
|
|
addi a0, sp, ABI_RA
|
|
|
|
|
REG_L a1, ABI_T0(sp)
|
riscv: Using PATCHABLE_FUNCTION_ENTRY instead of MCOUNT
This patch changes the current detour mechanism of dynamic ftrace
which has been discussed during LPC 2020 RISCV-MC [1].
Before the patch, we used mcount for detour:
<funca>:
addi sp,sp,-16
sd ra,8(sp)
sd s0,0(sp)
addi s0,sp,16
mv a5,ra
mv a0,a5
auipc ra,0x0 -> nop
jalr -296(ra) <_mcount@plt> ->nop
...
After the patch, we use nop call site area for detour:
<funca>:
nop -> REG_S ra, -SZREG(sp)
nop -> auipc ra, 0x?
nop -> jalr ?(ra)
nop -> REG_L ra, -SZREG(sp)
...
The mcount mechanism is mixed with gcc function prologue which is
not very clear. The patchable function entry just put 16 bytes nop
before the front of the function prologue which could be filled
with a separated detour mechanism.
[1] https://www.linuxplumbersconf.org/event/7/contributions/807/
Signed-off-by: Guo Ren <guoren@linux.alibaba.com>
Signed-off-by: Palmer Dabbelt <palmerdabbelt@google.com>
2020-12-17 16:01:41 +00:00
|
|
|
addi a1, a1, -FENTRY_RA_OFFSET
|
|
|
|
|
#ifdef HAVE_FUNCTION_GRAPH_FP_TEST
|
|
|
|
|
mv a2, s0
|
2018-02-13 13:13:18 +08:00
|
|
|
#endif
|
riscv: Using PATCHABLE_FUNCTION_ENTRY instead of MCOUNT
This patch changes the current detour mechanism of dynamic ftrace
which has been discussed during LPC 2020 RISCV-MC [1].
Before the patch, we used mcount for detour:
<funca>:
addi sp,sp,-16
sd ra,8(sp)
sd s0,0(sp)
addi s0,sp,16
mv a5,ra
mv a0,a5
auipc ra,0x0 -> nop
jalr -296(ra) <_mcount@plt> ->nop
...
After the patch, we use nop call site area for detour:
<funca>:
nop -> REG_S ra, -SZREG(sp)
nop -> auipc ra, 0x?
nop -> jalr ?(ra)
nop -> REG_L ra, -SZREG(sp)
...
The mcount mechanism is mixed with gcc function prologue which is
not very clear. The patchable function entry just put 16 bytes nop
before the front of the function prologue which could be filled
with a separated detour mechanism.
[1] https://www.linuxplumbersconf.org/event/7/contributions/807/
Signed-off-by: Guo Ren <guoren@linux.alibaba.com>
Signed-off-by: Palmer Dabbelt <palmerdabbelt@google.com>
2020-12-17 16:01:41 +00:00
|
|
|
ftrace_graph_call:
|
|
|
|
|
.global ftrace_graph_call
|
|
|
|
|
call ftrace_stub
|
|
|
|
|
#endif
|
|
|
|
|
RESTORE_ABI
|
riscv: ftrace: Reduce the detour code size to half
Use a temporary register to reduce the size of detour code from 16 bytes to
8 bytes. The previous implementation is from 'commit afc76b8b8011 ("riscv:
Using PATCHABLE_FUNCTION_ENTRY instead of MCOUNT")'.
Before the patch:
<func_prolog>:
0: REG_S ra, -SZREG(sp)
4: auipc ra, ?
8: jalr ?(ra)
12: REG_L ra, -SZREG(sp)
(func_boddy)
After the patch:
<func_prolog>:
0: auipc t0, ?
4: jalr t0, ?(t0)
(func_boddy)
This patch not just reduces the size of detour code, but also fixes an
important issue:
An Ftrace callback registered with FTRACE_OPS_FL_IPMODIFY flag can
actually change the instruction pointer, e.g. to "replace" the given
kernel function with a new one, which is needed for livepatching, etc.
In this case, the trampoline (ftrace_regs_caller) would not return to
<func_prolog+12> but would rather jump to the new function. So, "REG_L
ra, -SZREG(sp)" would not run and the original return address would not
be restored. The kernel is likely to hang or crash as a result.
This can be easily demonstrated if one tries to "replace", say,
cmdline_proc_show() with a new function with the same signature using
instruction_pointer_set(&fregs->regs, new_func_addr) in the Ftrace
callback.
Link: https://lore.kernel.org/linux-riscv/20221122075440.1165172-1-suagrfillet@gmail.com/
Link: https://lore.kernel.org/linux-riscv/d7d5730b-ebef-68e5-5046-e763e1ee6164@yadro.com/
Co-developed-by: Song Shuai <suagrfillet@gmail.com>
Signed-off-by: Song Shuai <suagrfillet@gmail.com>
Signed-off-by: Guo Ren <guoren@linux.alibaba.com>
Signed-off-by: Guo Ren <guoren@kernel.org>
Cc: Evgenii Shatokhin <e.shatokhin@yadro.com>
Reviewed-by: Evgenii Shatokhin <e.shatokhin@yadro.com>
Link: https://lore.kernel.org/r/20230112090603.1295340-4-guoren@kernel.org
Cc: stable@vger.kernel.org
Fixes: 10626c32e382 ("riscv/ftrace: Add basic support")
Signed-off-by: Palmer Dabbelt <palmer@rivosinc.com>
2023-01-12 04:05:59 -05:00
|
|
|
jr t0
|
2018-02-13 13:13:17 +08:00
|
|
|
ENDPROC(ftrace_caller)
|
2018-02-13 13:13:20 +08:00
|
|
|
|
|
|
|
|
#ifdef CONFIG_DYNAMIC_FTRACE_WITH_REGS
|
|
|
|
|
ENTRY(ftrace_regs_caller)
|
|
|
|
|
SAVE_ALL
|
|
|
|
|
|
riscv: ftrace: Reduce the detour code size to half
Use a temporary register to reduce the size of detour code from 16 bytes to
8 bytes. The previous implementation is from 'commit afc76b8b8011 ("riscv:
Using PATCHABLE_FUNCTION_ENTRY instead of MCOUNT")'.
Before the patch:
<func_prolog>:
0: REG_S ra, -SZREG(sp)
4: auipc ra, ?
8: jalr ?(ra)
12: REG_L ra, -SZREG(sp)
(func_boddy)
After the patch:
<func_prolog>:
0: auipc t0, ?
4: jalr t0, ?(t0)
(func_boddy)
This patch not just reduces the size of detour code, but also fixes an
important issue:
An Ftrace callback registered with FTRACE_OPS_FL_IPMODIFY flag can
actually change the instruction pointer, e.g. to "replace" the given
kernel function with a new one, which is needed for livepatching, etc.
In this case, the trampoline (ftrace_regs_caller) would not return to
<func_prolog+12> but would rather jump to the new function. So, "REG_L
ra, -SZREG(sp)" would not run and the original return address would not
be restored. The kernel is likely to hang or crash as a result.
This can be easily demonstrated if one tries to "replace", say,
cmdline_proc_show() with a new function with the same signature using
instruction_pointer_set(&fregs->regs, new_func_addr) in the Ftrace
callback.
Link: https://lore.kernel.org/linux-riscv/20221122075440.1165172-1-suagrfillet@gmail.com/
Link: https://lore.kernel.org/linux-riscv/d7d5730b-ebef-68e5-5046-e763e1ee6164@yadro.com/
Co-developed-by: Song Shuai <suagrfillet@gmail.com>
Signed-off-by: Song Shuai <suagrfillet@gmail.com>
Signed-off-by: Guo Ren <guoren@linux.alibaba.com>
Signed-off-by: Guo Ren <guoren@kernel.org>
Cc: Evgenii Shatokhin <e.shatokhin@yadro.com>
Reviewed-by: Evgenii Shatokhin <e.shatokhin@yadro.com>
Link: https://lore.kernel.org/r/20230112090603.1295340-4-guoren@kernel.org
Cc: stable@vger.kernel.org
Fixes: 10626c32e382 ("riscv/ftrace: Add basic support")
Signed-off-by: Palmer Dabbelt <palmer@rivosinc.com>
2023-01-12 04:05:59 -05:00
|
|
|
addi a0, t0, -FENTRY_RA_OFFSET
|
riscv: Using PATCHABLE_FUNCTION_ENTRY instead of MCOUNT
This patch changes the current detour mechanism of dynamic ftrace
which has been discussed during LPC 2020 RISCV-MC [1].
Before the patch, we used mcount for detour:
<funca>:
addi sp,sp,-16
sd ra,8(sp)
sd s0,0(sp)
addi s0,sp,16
mv a5,ra
mv a0,a5
auipc ra,0x0 -> nop
jalr -296(ra) <_mcount@plt> ->nop
...
After the patch, we use nop call site area for detour:
<funca>:
nop -> REG_S ra, -SZREG(sp)
nop -> auipc ra, 0x?
nop -> jalr ?(ra)
nop -> REG_L ra, -SZREG(sp)
...
The mcount mechanism is mixed with gcc function prologue which is
not very clear. The patchable function entry just put 16 bytes nop
before the front of the function prologue which could be filled
with a separated detour mechanism.
[1] https://www.linuxplumbersconf.org/event/7/contributions/807/
Signed-off-by: Guo Ren <guoren@linux.alibaba.com>
Signed-off-by: Palmer Dabbelt <palmerdabbelt@google.com>
2020-12-17 16:01:41 +00:00
|
|
|
la a1, function_trace_op
|
|
|
|
|
REG_L a2, 0(a1)
|
riscv: ftrace: Reduce the detour code size to half
Use a temporary register to reduce the size of detour code from 16 bytes to
8 bytes. The previous implementation is from 'commit afc76b8b8011 ("riscv:
Using PATCHABLE_FUNCTION_ENTRY instead of MCOUNT")'.
Before the patch:
<func_prolog>:
0: REG_S ra, -SZREG(sp)
4: auipc ra, ?
8: jalr ?(ra)
12: REG_L ra, -SZREG(sp)
(func_boddy)
After the patch:
<func_prolog>:
0: auipc t0, ?
4: jalr t0, ?(t0)
(func_boddy)
This patch not just reduces the size of detour code, but also fixes an
important issue:
An Ftrace callback registered with FTRACE_OPS_FL_IPMODIFY flag can
actually change the instruction pointer, e.g. to "replace" the given
kernel function with a new one, which is needed for livepatching, etc.
In this case, the trampoline (ftrace_regs_caller) would not return to
<func_prolog+12> but would rather jump to the new function. So, "REG_L
ra, -SZREG(sp)" would not run and the original return address would not
be restored. The kernel is likely to hang or crash as a result.
This can be easily demonstrated if one tries to "replace", say,
cmdline_proc_show() with a new function with the same signature using
instruction_pointer_set(&fregs->regs, new_func_addr) in the Ftrace
callback.
Link: https://lore.kernel.org/linux-riscv/20221122075440.1165172-1-suagrfillet@gmail.com/
Link: https://lore.kernel.org/linux-riscv/d7d5730b-ebef-68e5-5046-e763e1ee6164@yadro.com/
Co-developed-by: Song Shuai <suagrfillet@gmail.com>
Signed-off-by: Song Shuai <suagrfillet@gmail.com>
Signed-off-by: Guo Ren <guoren@linux.alibaba.com>
Signed-off-by: Guo Ren <guoren@kernel.org>
Cc: Evgenii Shatokhin <e.shatokhin@yadro.com>
Reviewed-by: Evgenii Shatokhin <e.shatokhin@yadro.com>
Link: https://lore.kernel.org/r/20230112090603.1295340-4-guoren@kernel.org
Cc: stable@vger.kernel.org
Fixes: 10626c32e382 ("riscv/ftrace: Add basic support")
Signed-off-by: Palmer Dabbelt <palmer@rivosinc.com>
2023-01-12 04:05:59 -05:00
|
|
|
mv a1, ra
|
riscv: Using PATCHABLE_FUNCTION_ENTRY instead of MCOUNT
This patch changes the current detour mechanism of dynamic ftrace
which has been discussed during LPC 2020 RISCV-MC [1].
Before the patch, we used mcount for detour:
<funca>:
addi sp,sp,-16
sd ra,8(sp)
sd s0,0(sp)
addi s0,sp,16
mv a5,ra
mv a0,a5
auipc ra,0x0 -> nop
jalr -296(ra) <_mcount@plt> ->nop
...
After the patch, we use nop call site area for detour:
<funca>:
nop -> REG_S ra, -SZREG(sp)
nop -> auipc ra, 0x?
nop -> jalr ?(ra)
nop -> REG_L ra, -SZREG(sp)
...
The mcount mechanism is mixed with gcc function prologue which is
not very clear. The patchable function entry just put 16 bytes nop
before the front of the function prologue which could be filled
with a separated detour mechanism.
[1] https://www.linuxplumbersconf.org/event/7/contributions/807/
Signed-off-by: Guo Ren <guoren@linux.alibaba.com>
Signed-off-by: Palmer Dabbelt <palmerdabbelt@google.com>
2020-12-17 16:01:41 +00:00
|
|
|
mv a3, sp
|
|
|
|
|
|
2018-02-13 13:13:20 +08:00
|
|
|
ftrace_regs_call:
|
|
|
|
|
.global ftrace_regs_call
|
|
|
|
|
call ftrace_stub
|
|
|
|
|
|
|
|
|
|
#ifdef CONFIG_FUNCTION_GRAPH_TRACER
|
riscv: Using PATCHABLE_FUNCTION_ENTRY instead of MCOUNT
This patch changes the current detour mechanism of dynamic ftrace
which has been discussed during LPC 2020 RISCV-MC [1].
Before the patch, we used mcount for detour:
<funca>:
addi sp,sp,-16
sd ra,8(sp)
sd s0,0(sp)
addi s0,sp,16
mv a5,ra
mv a0,a5
auipc ra,0x0 -> nop
jalr -296(ra) <_mcount@plt> ->nop
...
After the patch, we use nop call site area for detour:
<funca>:
nop -> REG_S ra, -SZREG(sp)
nop -> auipc ra, 0x?
nop -> jalr ?(ra)
nop -> REG_L ra, -SZREG(sp)
...
The mcount mechanism is mixed with gcc function prologue which is
not very clear. The patchable function entry just put 16 bytes nop
before the front of the function prologue which could be filled
with a separated detour mechanism.
[1] https://www.linuxplumbersconf.org/event/7/contributions/807/
Signed-off-by: Guo Ren <guoren@linux.alibaba.com>
Signed-off-by: Palmer Dabbelt <palmerdabbelt@google.com>
2020-12-17 16:01:41 +00:00
|
|
|
addi a0, sp, PT_RA
|
|
|
|
|
REG_L a1, PT_EPC(sp)
|
|
|
|
|
addi a1, a1, -FENTRY_RA_OFFSET
|
|
|
|
|
#ifdef HAVE_FUNCTION_GRAPH_FP_TEST
|
|
|
|
|
mv a2, s0
|
|
|
|
|
#endif
|
|
|
|
|
ftrace_graph_regs_call:
|
|
|
|
|
.global ftrace_graph_regs_call
|
|
|
|
|
call ftrace_stub
|
2018-02-13 13:13:20 +08:00
|
|
|
#endif
|
|
|
|
|
|
|
|
|
|
RESTORE_ALL
|
riscv: ftrace: Reduce the detour code size to half
Use a temporary register to reduce the size of detour code from 16 bytes to
8 bytes. The previous implementation is from 'commit afc76b8b8011 ("riscv:
Using PATCHABLE_FUNCTION_ENTRY instead of MCOUNT")'.
Before the patch:
<func_prolog>:
0: REG_S ra, -SZREG(sp)
4: auipc ra, ?
8: jalr ?(ra)
12: REG_L ra, -SZREG(sp)
(func_boddy)
After the patch:
<func_prolog>:
0: auipc t0, ?
4: jalr t0, ?(t0)
(func_boddy)
This patch not just reduces the size of detour code, but also fixes an
important issue:
An Ftrace callback registered with FTRACE_OPS_FL_IPMODIFY flag can
actually change the instruction pointer, e.g. to "replace" the given
kernel function with a new one, which is needed for livepatching, etc.
In this case, the trampoline (ftrace_regs_caller) would not return to
<func_prolog+12> but would rather jump to the new function. So, "REG_L
ra, -SZREG(sp)" would not run and the original return address would not
be restored. The kernel is likely to hang or crash as a result.
This can be easily demonstrated if one tries to "replace", say,
cmdline_proc_show() with a new function with the same signature using
instruction_pointer_set(&fregs->regs, new_func_addr) in the Ftrace
callback.
Link: https://lore.kernel.org/linux-riscv/20221122075440.1165172-1-suagrfillet@gmail.com/
Link: https://lore.kernel.org/linux-riscv/d7d5730b-ebef-68e5-5046-e763e1ee6164@yadro.com/
Co-developed-by: Song Shuai <suagrfillet@gmail.com>
Signed-off-by: Song Shuai <suagrfillet@gmail.com>
Signed-off-by: Guo Ren <guoren@linux.alibaba.com>
Signed-off-by: Guo Ren <guoren@kernel.org>
Cc: Evgenii Shatokhin <e.shatokhin@yadro.com>
Reviewed-by: Evgenii Shatokhin <e.shatokhin@yadro.com>
Link: https://lore.kernel.org/r/20230112090603.1295340-4-guoren@kernel.org
Cc: stable@vger.kernel.org
Fixes: 10626c32e382 ("riscv/ftrace: Add basic support")
Signed-off-by: Palmer Dabbelt <palmer@rivosinc.com>
2023-01-12 04:05:59 -05:00
|
|
|
jr t0
|
2018-02-13 13:13:20 +08:00
|
|
|
ENDPROC(ftrace_regs_caller)
|
|
|
|
|
#endif /* CONFIG_DYNAMIC_FTRACE_WITH_REGS */
|