RISC-V: vDSO: Wire up getrandom() vDSO implementation

Hook up the generic vDSO implementation to the generic vDSO getrandom
implementation by providing the required __arch_chacha20_blocks_nostack
and getrandom_syscall implementations. Also wire up the selftests.

The benchmark result:

	vdso: 25000000 times in 2.466341333 seconds
	libc: 25000000 times in 41.447720005 seconds
	syscall: 25000000 times in 41.043926672 seconds

	vdso: 25000000 x 256 times in 162.286219353 seconds
	libc: 25000000 x 256 times in 2953.855018685 seconds
	syscall: 25000000 x 256 times in 2796.268546000 seconds

[ alex: - Fix dynamic relocation
        - Squash Nathan's fix https://lore.kernel.org/all/20250423-riscv-fix-compat_vdso-lld-v2-1-b7bbbc244501@kernel.org/
	- Add comment from Loongarch ]

Signed-off-by: Xi Ruoyao <xry111@xry111.site>
Link: https://lore.kernel.org/r/20250411024600.16045-1-xry111@xry111.site
Tested-by: Alexandre Ghiti <alexghiti@rivosinc.com>
Signed-off-by: Alexandre Ghiti <alexghiti@rivosinc.com>
Signed-off-by: Palmer Dabbelt <palmer@dabbelt.com>

arch/riscv/Kconfig

@@ -219,6 +219,7 @@ config RISCV
 	select THREAD_INFO_IN_TASK
 	select TRACE_IRQFLAGS_SUPPORT
 	select UACCESS_MEMCPY if !MMU
+	select VDSO_GETRANDOM if HAVE_GENERIC_VDSO
 	select USER_STACKTRACE_SUPPORT
 	select ZONE_DMA32 if 64BIT
 

arch/riscv/include/asm/vdso/getrandom.h

@@ -0,0 +1,30 @@
+/* SPDX-License-Identifier: GPL-2.0-only */
+/*
+ * Copyright (C) 2025 Xi Ruoyao <xry111@xry111.site>. All Rights Reserved.
+ */
+#ifndef __ASM_VDSO_GETRANDOM_H
+#define __ASM_VDSO_GETRANDOM_H
+
+#ifndef __ASSEMBLY__
+
+#include <asm/unistd.h>
+
+static __always_inline ssize_t getrandom_syscall(void *_buffer, size_t _len, unsigned int _flags)
+{
+	register long ret asm("a0");
+	register long nr asm("a7") = __NR_getrandom;
+	register void *buffer asm("a0") = _buffer;
+	register size_t len asm("a1") = _len;
+	register unsigned int flags asm("a2") = _flags;
+
+	asm volatile ("ecall\n"
+		      : "+r" (ret)
+		      : "r" (nr), "r" (buffer), "r" (len), "r" (flags)
+		      : "memory");
+
+	return ret;
+}
+
+#endif /* !__ASSEMBLY__ */
+
+#endif /* __ASM_VDSO_GETRANDOM_H */

arch/riscv/kernel/vdso/Makefile

@@ -13,9 +13,17 @@ vdso-syms += flush_icache
 vdso-syms += hwprobe
 vdso-syms += sys_hwprobe
 
+ifdef CONFIG_VDSO_GETRANDOM
+vdso-syms += getrandom
+endif
+
 # Files to link into the vdso
 obj-vdso = $(patsubst %, %.o, $(vdso-syms)) note.o
 
+ifdef CONFIG_VDSO_GETRANDOM
+obj-vdso += vgetrandom-chacha.o
+endif
+
 ccflags-y := -fno-stack-protector
 ccflags-y += -DDISABLE_BRANCH_PROFILING
 ccflags-y += -fno-builtin
@@ -24,6 +32,10 @@ ifneq ($(c-gettimeofday-y),)
   CFLAGS_vgettimeofday.o += -fPIC -include $(c-gettimeofday-y)
 endif
 
+ifneq ($(c-getrandom-y),)
+  CFLAGS_getrandom.o += -fPIC -include $(c-getrandom-y)
+endif
+
 CFLAGS_hwprobe.o += -fPIC
 
 # Build rules
@@ -38,6 +50,7 @@ endif
 
 # Disable -pg to prevent insert call site
 CFLAGS_REMOVE_vgettimeofday.o = $(CC_FLAGS_FTRACE) $(CC_FLAGS_SCS)
+CFLAGS_REMOVE_getrandom.o = $(CC_FLAGS_FTRACE) $(CC_FLAGS_SCS)
 CFLAGS_REMOVE_hwprobe.o = $(CC_FLAGS_FTRACE) $(CC_FLAGS_SCS)
 
 # Force dependency

arch/riscv/kernel/vdso/getrandom.c

@@ -0,0 +1,10 @@
+// SPDX-License-Identifier: GPL-2.0-only
+/*
+ * Copyright (C) 2025 Xi Ruoyao <xry111@xry111.site>. All Rights Reserved.
+ */
+#include <linux/types.h>
+
+ssize_t __vdso_getrandom(void *buffer, size_t len, unsigned int flags, void *opaque_state, size_t opaque_len)
+{
+	return __cvdso_getrandom(buffer, len, flags, opaque_state, opaque_len);
+}

arch/riscv/kernel/vdso/vdso.lds.S

@@ -79,6 +79,9 @@ VERSION
 		__vdso_flush_icache;
 #ifndef COMPAT_VDSO
 		__vdso_riscv_hwprobe;
+#endif
+#if defined(CONFIG_VDSO_GETRANDOM) && !defined(COMPAT_VDSO)
+		__vdso_getrandom;
 #endif
 	local: *;
 	};

arch/riscv/kernel/vdso/vgetrandom-chacha.S

@@ -0,0 +1,249 @@
+/* SPDX-License-Identifier: GPL-2.0 */
+/*
+ * Copyright (C) 2025 Xi Ruoyao <xry111@xry111.site>. All Rights Reserved.
+ *
+ * Based on arch/loongarch/vdso/vgetrandom-chacha.S.
+ */
+
+#include <asm/asm.h>
+#include <linux/linkage.h>
+
+.text
+
+.macro	ROTRI	rd rs imm
+	slliw	t0, \rs, 32 - \imm
+	srliw	\rd, \rs, \imm
+	or	\rd, \rd, t0
+.endm
+
+.macro	OP_4REG	op d0 d1 d2 d3 s0 s1 s2 s3
+	\op	\d0, \d0, \s0
+	\op	\d1, \d1, \s1
+	\op	\d2, \d2, \s2
+	\op	\d3, \d3, \s3
+.endm
+
+/*
+ *	a0: output bytes
+ * 	a1: 32-byte key input
+ *	a2: 8-byte counter input/output
+ *	a3: number of 64-byte blocks to write to output
+ */
+SYM_FUNC_START(__arch_chacha20_blocks_nostack)
+
+#define output		a0
+#define key		a1
+#define counter		a2
+#define nblocks		a3
+#define i		a4
+#define state0		s0
+#define state1		s1
+#define state2		s2
+#define state3		s3
+#define state4		s4
+#define state5		s5
+#define state6		s6
+#define state7		s7
+#define state8		s8
+#define state9		s9
+#define state10		s10
+#define state11		s11
+#define state12		a5
+#define state13		a6
+#define state14		a7
+#define state15		t1
+#define cnt		t2
+#define copy0		t3
+#define copy1		t4
+#define copy2		t5
+#define copy3		t6
+
+/* Packs to be used with OP_4REG */
+#define line0		state0, state1, state2, state3
+#define line1		state4, state5, state6, state7
+#define line2		state8, state9, state10, state11
+#define line3		state12, state13, state14, state15
+
+#define line1_perm	state5, state6, state7, state4
+#define line2_perm	state10, state11, state8, state9
+#define line3_perm	state15, state12, state13, state14
+
+#define copy		copy0, copy1, copy2, copy3
+
+#define _16		16, 16, 16, 16
+#define _20		20, 20, 20, 20
+#define _24		24, 24, 24, 24
+#define _25		25, 25, 25, 25
+
+	/*
+	 * The ABI requires s0-s9 saved.
+	 * This does not violate the stack-less requirement: no sensitive data
+	 * is spilled onto the stack.
+	 */
+	addi		sp, sp, -12*SZREG
+	REG_S		s0,         (sp)
+	REG_S		s1,    SZREG(sp)
+	REG_S		s2,  2*SZREG(sp)
+	REG_S		s3,  3*SZREG(sp)
+	REG_S		s4,  4*SZREG(sp)
+	REG_S		s5,  5*SZREG(sp)
+	REG_S		s6,  6*SZREG(sp)
+	REG_S		s7,  7*SZREG(sp)
+	REG_S		s8,  8*SZREG(sp)
+	REG_S		s9,  9*SZREG(sp)
+	REG_S		s10, 10*SZREG(sp)
+	REG_S		s11, 11*SZREG(sp)
+
+	ld		cnt, (counter)
+
+	li		copy0, 0x61707865
+	li		copy1, 0x3320646e
+	li		copy2, 0x79622d32
+	li		copy3, 0x6b206574
+
+.Lblock:
+	/* state[0,1,2,3] = "expand 32-byte k" */
+	mv		state0, copy0
+	mv		state1, copy1
+	mv		state2, copy2
+	mv		state3, copy3
+
+	/* state[4,5,..,11] = key */
+	lw		state4,   (key)
+	lw		state5,  4(key)
+	lw		state6,  8(key)
+	lw		state7,  12(key)
+	lw		state8,  16(key)
+	lw		state9,  20(key)
+	lw		state10, 24(key)
+	lw		state11, 28(key)
+
+	/* state[12,13] = counter */
+	mv		state12, cnt
+	srli		state13, cnt, 32
+
+	/* state[14,15] = 0 */
+	mv		state14, zero
+	mv		state15, zero
+
+	li		i, 10
+.Lpermute:
+	/* odd round */
+	OP_4REG	addw	line0, line1
+	OP_4REG	xor	line3, line0
+	OP_4REG	ROTRI	line3, _16
+
+	OP_4REG	addw	line2, line3
+	OP_4REG	xor	line1, line2
+	OP_4REG	ROTRI	line1, _20
+
+	OP_4REG	addw	line0, line1
+	OP_4REG	xor	line3, line0
+	OP_4REG	ROTRI	line3, _24
+
+	OP_4REG	addw	line2, line3
+	OP_4REG	xor	line1, line2
+	OP_4REG	ROTRI	line1, _25
+
+	/* even round */
+	OP_4REG	addw	line0, line1_perm
+	OP_4REG	xor	line3_perm, line0
+	OP_4REG	ROTRI	line3_perm, _16
+
+	OP_4REG	addw	line2_perm, line3_perm
+	OP_4REG	xor	line1_perm, line2_perm
+	OP_4REG	ROTRI	line1_perm, _20
+
+	OP_4REG	addw	line0, line1_perm
+	OP_4REG	xor	line3_perm, line0
+	OP_4REG	ROTRI	line3_perm, _24
+
+	OP_4REG	addw	line2_perm, line3_perm
+	OP_4REG	xor	line1_perm, line2_perm
+	OP_4REG	ROTRI	line1_perm, _25
+
+	addi		i, i, -1
+	bnez		i, .Lpermute
+
+	/* output[0,1,2,3] = copy[0,1,2,3] + state[0,1,2,3] */
+	OP_4REG	addw	line0, copy
+	sw		state0,   (output)
+	sw		state1,  4(output)
+	sw		state2,  8(output)
+	sw		state3, 12(output)
+
+	/* from now on state[0,1,2,3] are scratch registers  */
+
+	/* state[0,1,2,3] = lo(key) */
+	lw		state0,   (key)
+	lw		state1,  4(key)
+	lw		state2,  8(key)
+	lw		state3, 12(key)
+
+	/* output[4,5,6,7] = state[0,1,2,3] + state[4,5,6,7] */
+	OP_4REG	addw	line1, line0
+	sw		state4, 16(output)
+	sw		state5, 20(output)
+	sw		state6, 24(output)
+	sw		state7, 28(output)
+
+	/* state[0,1,2,3] = hi(key) */
+	lw		state0, 16(key)
+	lw		state1, 20(key)
+	lw		state2, 24(key)
+	lw		state3, 28(key)
+
+	/* output[8,9,10,11] = tmp[0,1,2,3] + state[8,9,10,11] */
+	OP_4REG	addw	line2, line0
+	sw		state8,  32(output)
+	sw		state9,  36(output)
+	sw		state10, 40(output)
+	sw		state11, 44(output)
+
+	/* output[12,13,14,15] = state[12,13,14,15] + [cnt_lo, cnt_hi, 0, 0] */
+	addw		state12, state12, cnt
+	srli		state0, cnt, 32
+	addw		state13, state13, state0
+	sw		state12, 48(output)
+	sw		state13, 52(output)
+	sw		state14, 56(output)
+	sw		state15, 60(output)
+
+	/* ++counter */
+	addi		cnt, cnt, 1
+
+	/* output += 64 */
+	addi		output, output, 64
+	/* --nblocks */
+	addi		nblocks, nblocks, -1
+	bnez		nblocks, .Lblock
+
+	/* counter = [cnt_lo, cnt_hi] */
+	sd		cnt, (counter)
+
+	/* Zero out the potentially sensitive regs, in case nothing uses these
+	 * again.  As at now copy[0,1,2,3] just contains "expand 32-byte k" and
+	 * state[0,...,11] are s0-s11 those we'll restore in the epilogue, we
+	 * only need to zero state[12,...,15].
+	 */
+	mv		state12, zero
+	mv		state13, zero
+	mv		state14, zero
+	mv		state15, zero
+
+	REG_L		s0,         (sp)
+	REG_L		s1,    SZREG(sp)
+	REG_L		s2,  2*SZREG(sp)
+	REG_L		s3,  3*SZREG(sp)
+	REG_L		s4,  4*SZREG(sp)
+	REG_L		s5,  5*SZREG(sp)
+	REG_L		s6,  6*SZREG(sp)
+	REG_L		s7,  7*SZREG(sp)
+	REG_L		s8,  8*SZREG(sp)
+	REG_L		s9,  9*SZREG(sp)
+	REG_L		s10, 10*SZREG(sp)
+	REG_L		s11, 11*SZREG(sp)
+	addi		sp, sp, 12*SZREG
+
+	ret
+SYM_FUNC_END(__arch_chacha20_blocks_nostack)

tools/testing/selftests/vDSO/vgetrandom-chacha.S

@@ -11,6 +11,8 @@
 #include "../../../../arch/loongarch/vdso/vgetrandom-chacha.S"
 #elif defined(__powerpc__) || defined(__powerpc64__)
 #include "../../../../arch/powerpc/kernel/vdso/vgetrandom-chacha.S"
+#elif defined(__riscv) && __riscv_xlen == 64
+#include "../../../../arch/riscv/kernel/vdso/vgetrandom-chacha.S"
 #elif defined(__s390x__)
 #include "../../../../arch/s390/kernel/vdso64/vgetrandom-chacha.S"
 #elif defined(__x86_64__)