public-mirrors/linux
1
0
Fork 0
mirror of git://git.kernel.org/pub/scm/linux/kernel/git/torvalds/linux.git synced 2025-08-04 16:25:34 +00:00
Code Issues Projects Releases Packages Wiki Activity Actions

x86/boot/64: Simplify global variable accesses in GDT/IDT programming

Browse source 
There are two code paths in the startup code to program an IDT: one that
runs from the 1:1 mapping and one that runs from the virtual kernel
mapping. Currently, these are strictly separate because fixup_pointer()
is used on the 1:1 path, which will produce the wrong value when used
while executing from the virtual kernel mapping.

Switch to RIP_REL_REF() so that the two code paths can be merged. Also,
move the GDT and IDT descriptors to the stack so that they can be
referenced directly, rather than via RIP_REL_REF().

Rename startup_64_setup_env() to startup_64_setup_gdt_idt() while at it,
to make the call from assembler self-documenting.

Signed-off-by: Ard Biesheuvel <ardb@kernel.org>
Signed-off-by: Borislav Petkov (AMD) <bp@alien8.de>
Signed-off-by: Ard Biesheuvel <ardb@kernel.org>
Signed-off-by: Ingo Molnar <mingo@kernel.org>
Link: https://lore.kernel.org/r/20240221113506.2565718-19-ardb+git@google.com
This commit is contained in:
Ard Biesheuvel 2024-02-21 12:35:08 +01:00 • committed by Ingo Molnar
parent 2e5fc4786b
commit 5da7936719
3 changed files with 32 additions and 49 deletions
Show stats Download patch file Download diff file Expand all files Collapse all files

2
arch/x86/include/asm/setup.h
View file

@ -48,7 +48,7 @@ extern unsigned long saved_video_mode;
extern void reserve_standard_io_resources(void);
extern void i386_reserve_resources(void);
extern unsigned long __startup_64(unsigned long physaddr, struct boot_params *bp);
extern void startup_64_setup_env(unsigned long physbase);
extern void startup_64_setup_gdt_idt(void);
extern void early_setup_idt(void);
extern void __init do_early_exception(struct pt_regs *regs, int trapnr);

75
arch/x86/kernel/head64.c
View file

@ -22,6 +22,7 @@
#include <linux/cc_platform.h>
#include <linux/pgtable.h>
#include <asm/asm.h>
#include <asm/processor.h>
#include <asm/proto.h>
#include <asm/smp.h>
@ -76,15 +77,6 @@ static struct desc_struct startup_gdt[GDT_ENTRIES] __initdata = {
[GDT_ENTRY_KERNEL_DS] = GDT_ENTRY_INIT(DESC_DATA64, 0, 0xfffff),
};
/*
* Address needs to be set at runtime because it references the startup_gdt
* while the kernel still uses a direct mapping.
*/
static struct desc_ptr startup_gdt_descr __initdata = {
.size = sizeof(startup_gdt)-1,
.address = 0,
};
static void __head *fixup_pointer(void *ptr, unsigned long physaddr)
{
return ptr - (void *)_text + (void *)physaddr;
@ -569,62 +561,52 @@ void __init __noreturn x86_64_start_reservations(char *real_mode_data)
*/
static gate_desc bringup_idt_table[NUM_EXCEPTION_VECTORS] __page_aligned_data;
static struct desc_ptr bringup_idt_descr = {
.size = (NUM_EXCEPTION_VECTORS * sizeof(gate_desc)) - 1,
.address = 0, /* Set at runtime */
};
static void set_bringup_idt_handler(gate_desc *idt, int n, void *handler)
/* This may run while still in the direct mapping */
static void __head startup_64_load_idt(void *vc_handler)
{
#ifdef CONFIG_AMD_MEM_ENCRYPT
struct desc_ptr desc = {
.address = (unsigned long)&RIP_REL_REF(bringup_idt_table),
.size = sizeof(bringup_idt_table) - 1,
};
struct idt_data data;
gate_desc desc;
gate_desc idt_desc;
init_idt_data(&data, n, handler);
idt_init_desc(&desc, &data);
native_write_idt_entry(idt, n, &desc);
#endif
}
/* This runs while still in the direct mapping */
static void __head startup_64_load_idt(unsigned long physbase)
{
struct desc_ptr *desc = fixup_pointer(&bringup_idt_descr, physbase);
gate_desc *idt = fixup_pointer(bringup_idt_table, physbase);
if (IS_ENABLED(CONFIG_AMD_MEM_ENCRYPT)) {
void *handler;
/* VMM Communication Exception */
handler = fixup_pointer(vc_no_ghcb, physbase);
set_bringup_idt_handler(idt, X86_TRAP_VC, handler);
/* @vc_handler is set only for a VMM Communication Exception */
if (vc_handler) {
init_idt_data(&data, X86_TRAP_VC, vc_handler);
idt_init_desc(&idt_desc, &data);
native_write_idt_entry((gate_desc *)desc.address, X86_TRAP_VC, &idt_desc);
}
desc->address = (unsigned long)idt;
native_load_idt(desc);
native_load_idt(&desc);
}
/* This is used when running on kernel addresses */
void early_setup_idt(void)
{
/* VMM Communication Exception */
void *handler = NULL;
if (IS_ENABLED(CONFIG_AMD_MEM_ENCRYPT)) {
setup_ghcb();
set_bringup_idt_handler(bringup_idt_table, X86_TRAP_VC, vc_boot_ghcb);
handler = vc_boot_ghcb;
}
bringup_idt_descr.address = (unsigned long)bringup_idt_table;
native_load_idt(&bringup_idt_descr);
startup_64_load_idt(handler);
}
/*
* Setup boot CPU state needed before kernel switches to virtual addresses.
*/
void __head startup_64_setup_env(unsigned long physbase)
void __head startup_64_setup_gdt_idt(void)
{
void *handler = NULL;
struct desc_ptr startup_gdt_descr = {
.address = (unsigned long)&RIP_REL_REF(startup_gdt),
.size = sizeof(startup_gdt) - 1,
};
/* Load GDT */
startup_gdt_descr.address = (unsigned long)fixup_pointer(startup_gdt, physbase);
native_load_gdt(&startup_gdt_descr);
/* New GDT is live - reload data segment registers */
@ -632,5 +614,8 @@ void __head startup_64_setup_env(unsigned long physbase)
"movl %%eax, %%ss\n"
"movl %%eax, %%es\n" : : "a"(__KERNEL_DS) : "memory");
startup_64_load_idt(physbase);
if (IS_ENABLED(CONFIG_AMD_MEM_ENCRYPT))
handler = &RIP_REL_REF(vc_no_ghcb);
startup_64_load_idt(handler);
}

4
arch/x86/kernel/head_64.S
View file

@ -68,8 +68,6 @@ SYM_CODE_START_NOALIGN(startup_64)
/* Set up the stack for verify_cpu() */
leaq (__end_init_task - PTREGS_SIZE)(%rip), %rsp
leaq _text(%rip), %rdi
/* Setup GSBASE to allow stack canary access for C code */
movl $MSR_GS_BASE, %ecx
leaq INIT_PER_CPU_VAR(fixed_percpu_data)(%rip), %rdx
@ -77,7 +75,7 @@ SYM_CODE_START_NOALIGN(startup_64)
shrq $32, %rdx
wrmsr
call startup_64_setup_env
call startup_64_setup_gdt_idt
/* Now switch to __KERNEL_CS so IRET works reliably */
pushq $__KERNEL_CS