arm64: vDSO: Wire up getrandom() vDSO implementation

Hook up the generic vDSO implementation to the aarch64 vDSO data page.
The _vdso_rng_data required data is placed within the _vdso_data vvar
page, by using a offset larger than the vdso_data.

The vDSO function requires a ChaCha20 implementation that does not write
to the stack, and that can do an entire ChaCha20 permutation.  The one
provided uses NEON on the permute operation, with a fallback to the
syscall for chips that do not support AdvSIMD.

This also passes the vdso_test_chacha test along with
vdso_test_getrandom. The vdso_test_getrandom bench-single result on
Neoverse-N1 shows:

   vdso: 25000000 times in 0.783884250 seconds
   libc: 25000000 times in 8.780275399 seconds
syscall: 25000000 times in 8.786581518 seconds

A small fixup to arch/arm64/include/asm/mman.h was required to avoid
pulling kernel code into the vDSO, similar to what's already done in
arch/arm64/include/asm/rwonce.h.
Signed-off-by: Adhemerval Zanella <adhemerval.zanella@linaro.org>
Reviewed-by: Ard Biesheuvel <ardb@kernel.org>
Acked-by: Will Deacon <will@kernel.org>
Signed-off-by: Jason A. Donenfeld <Jason@zx2c4.com>

arch/arm64/Kconfig

@@ -262,6 +262,7 @@ config ARM64
 	select TRACE_IRQFLAGS_NMI_SUPPORT
 	select HAVE_SOFTIRQ_ON_OWN_STACK
 	select USER_STACKTRACE_SUPPORT
+	select VDSO_GETRANDOM
 	help
 	  ARM 64-bit (AArch64) Linux support.
 

arch/arm64/include/asm/mman.h

@@ -2,9 +2,11 @@
 #ifndef __ASM_MMAN_H__
 #define __ASM_MMAN_H__
 
+#include <uapi/asm/mman.h>
+
+#ifndef BUILD_VDSO
 #include <linux/compiler.h>
 #include <linux/types.h>
-#include <uapi/asm/mman.h>
 
 static inline unsigned long arch_calc_vm_prot_bits(unsigned long prot,
 	unsigned long pkey __always_unused)
@@ -60,4 +62,6 @@ static inline bool arch_validate_flags(unsigned long vm_flags)
 }
 #define arch_validate_flags(vm_flags) arch_validate_flags(vm_flags)
 
+#endif /* !BUILD_VDSO */
+
 #endif /* ! __ASM_MMAN_H__ */

arch/arm64/include/asm/vdso/getrandom.h

+/* SPDX-License-Identifier: GPL-2.0 */
+
+#ifndef __ASM_VDSO_GETRANDOM_H
+#define __ASM_VDSO_GETRANDOM_H
+
+#ifndef __ASSEMBLY__
+
+#include <asm/unistd.h>
+#include <asm/vdso/vsyscall.h>
+#include <vdso/datapage.h>
+
+/**
+ * getrandom_syscall - Invoke the getrandom() syscall.
+ * @buffer:	Destination buffer to fill with random bytes.
+ * @len:	Size of @buffer in bytes.
+ * @flags:	Zero or more GRND_* flags.
+ * Returns:	The number of random bytes written to @buffer, or a negative value indicating an error.
+ */
+static __always_inline ssize_t getrandom_syscall(void *_buffer, size_t _len, unsigned int _flags)
+{
+	register void *buffer asm ("x0") = _buffer;
+	register size_t len asm ("x1") = _len;
+	register unsigned int flags asm ("x2") = _flags;
+	register long ret asm ("x0");
+	register long nr asm ("x8") = __NR_getrandom;
+
+	asm volatile(
+	"       svc #0\n"
+	: "=r" (ret)
+	: "r" (buffer), "r" (len), "r" (flags), "r" (nr)
+	: "memory");
+
+	return ret;
+}
+
+static __always_inline const struct vdso_rng_data *__arch_get_vdso_rng_data(void)
+{
+	/*
+	 * The RNG data is in the real VVAR data page, but if a task belongs to a time namespace
+	 * then VVAR_DATA_PAGE_OFFSET points to the namespace-specific VVAR page and VVAR_TIMENS_
+	 * PAGE_OFFSET points to the real VVAR page.
+	 */
+	if (IS_ENABLED(CONFIG_TIME_NS) && _vdso_data->clock_mode == VDSO_CLOCKMODE_TIMENS)
+		return (void *)&_vdso_rng_data + VVAR_TIMENS_PAGE_OFFSET * (1UL << CONFIG_PAGE_SHIFT);
+	return &_vdso_rng_data;
+}
+
+#endif /* !__ASSEMBLY__ */
+
+#endif /* __ASM_VDSO_GETRANDOM_H */

arch/arm64/include/asm/vdso/vsyscall.h

@@ -2,11 +2,19 @@
 #ifndef __ASM_VDSO_VSYSCALL_H
 #define __ASM_VDSO_VSYSCALL_H
 
+#define __VDSO_RND_DATA_OFFSET  480
+
 #ifndef __ASSEMBLY__
 
 #include <linux/timekeeper_internal.h>
 #include <vdso/datapage.h>
 
+enum vvar_pages {
+	VVAR_DATA_PAGE_OFFSET,
+	VVAR_TIMENS_PAGE_OFFSET,
+	VVAR_NR_PAGES,
+};
+
 #define VDSO_PRECISION_MASK	~(0xFF00ULL<<48)
 
 extern struct vdso_data *vdso_data;
@@ -21,6 +29,13 @@ struct vdso_data *__arm64_get_k_vdso_data(void)
 }
 #define __arch_get_k_vdso_data __arm64_get_k_vdso_data
 
+static __always_inline
+struct vdso_rng_data *__arm64_get_k_vdso_rnd_data(void)
+{
+	return (void *)vdso_data + __VDSO_RND_DATA_OFFSET;
+}
+#define __arch_get_k_vdso_rng_data __arm64_get_k_vdso_rnd_data
+
 static __always_inline
 void __arm64_update_vsyscall(struct vdso_data *vdata, struct timekeeper *tk)
 {

arch/arm64/kernel/vdso.c

@@ -34,12 +34,6 @@ enum vdso_abi {
 	VDSO_ABI_AA32,
 };
 
-enum vvar_pages {
-	VVAR_DATA_PAGE_OFFSET,
-	VVAR_TIMENS_PAGE_OFFSET,
-	VVAR_NR_PAGES,
-};
-
 struct vdso_abi_info {
 	const char *name;
 	const char *vdso_code_start;

arch/arm64/kernel/vdso/Makefile

@@ -9,7 +9,7 @@
 # Include the generic Makefile to check the built vdso.
 include $(srctree)/lib/vdso/Makefile
 
-obj-vdso := vgettimeofday.o note.o sigreturn.o
+obj-vdso := vgettimeofday.o note.o sigreturn.o vgetrandom.o vgetrandom-chacha.o
 
 # Build rules
 targets := $(obj-vdso) vdso.so vdso.so.dbg
@@ -34,19 +34,28 @@ ccflags-y := -fno-common -fno-builtin -fno-stack-protector -ffixed-x18
 ccflags-y += -DDISABLE_BRANCH_PROFILING -DBUILD_VDSO
 
 # -Wmissing-prototypes and -Wmissing-declarations are removed from
-# the CFLAGS of vgettimeofday.c to make possible to build the
-# kernel with CONFIG_WERROR enabled.
-CFLAGS_REMOVE_vgettimeofday.o = $(CC_FLAGS_FTRACE) -Os $(CC_FLAGS_SCS) \
+# the CFLAGS to make possible to build the kernel with CONFIG_WERROR enabled.
+CC_FLAGS_REMOVE_VDSO := $(CC_FLAGS_FTRACE) -Os $(CC_FLAGS_SCS) \
 			$(RANDSTRUCT_CFLAGS) $(GCC_PLUGINS_CFLAGS) \
 			$(CC_FLAGS_LTO) $(CC_FLAGS_CFI) \
 			-Wmissing-prototypes -Wmissing-declarations
 
-CFLAGS_vgettimeofday.o = -O2 -mcmodel=tiny -fasynchronous-unwind-tables
+CC_FLAGS_ADD_VDSO := -O2 -mcmodel=tiny -fasynchronous-unwind-tables
+
+CFLAGS_REMOVE_vgettimeofday.o = $(CC_FLAGS_REMOVE_VDSO)
+CFLAGS_REMOVE_vgetrandom.o = $(CC_FLAGS_REMOVE_VDSO)
+
+CFLAGS_vgettimeofday.o = $(CC_FLAGS_ADD_VDSO)
+CFLAGS_vgetrandom.o = $(CC_FLAGS_ADD_VDSO)
 
 ifneq ($(c-gettimeofday-y),)
   CFLAGS_vgettimeofday.o += -include $(c-gettimeofday-y)
 endif
 
+ifneq ($(c-getrandom-y),)
+  CFLAGS_vgetrandom.o += -include $(c-getrandom-y)
+endif
+
 targets += vdso.lds
 CPPFLAGS_vdso.lds += -P -C -U$(ARCH)
 

arch/arm64/kernel/vdso/vdso.lds.S

@@ -11,7 +11,9 @@
 #include <linux/const.h>
 #include <asm/page.h>
 #include <asm/vdso.h>
+#include <asm/vdso/vsyscall.h>
 #include <asm-generic/vmlinux.lds.h>
+#include <vdso/datapage.h>
 
 OUTPUT_FORMAT("elf64-littleaarch64", "elf64-bigaarch64", "elf64-littleaarch64")
 OUTPUT_ARCH(aarch64)
@@ -19,6 +21,7 @@ OUTPUT_ARCH(aarch64)
 SECTIONS
 {
 	PROVIDE(_vdso_data = . - __VVAR_PAGES * PAGE_SIZE);
+	PROVIDE(_vdso_rng_data = _vdso_data + __VDSO_RND_DATA_OFFSET);
 #ifdef CONFIG_TIME_NS
 	PROVIDE(_timens_data = _vdso_data + PAGE_SIZE);
 #endif
@@ -102,6 +105,7 @@ VERSION
 		__kernel_gettimeofday;
 		__kernel_clock_gettime;
 		__kernel_clock_getres;
+		__kernel_getrandom;
 	local: *;
 	};
 }

arch/arm64/kernel/vdso/vgetrandom-chacha.S

+// SPDX-License-Identifier: GPL-2.0
+
+#include <linux/linkage.h>
+#include <asm/cache.h>
+#include <asm/assembler.h>
+
+	.text
+
+#define state0		v0
+#define state1		v1
+#define state2		v2
+#define state3		v3
+#define copy0		v4
+#define copy0_q		q4
+#define copy1		v5
+#define copy2		v6
+#define copy3		v7
+#define copy3_d		d7
+#define one_d		d16
+#define one_q		q16
+#define one_v		v16
+#define tmp		v17
+#define rot8		v18
+
+/*
+ * ARM64 ChaCha20 implementation meant for vDSO.  Produces a given positive
+ * number of blocks of output with nonce 0, taking an input key and 8-bytes
+ * counter.  Importantly does not spill to the stack.
+ *
+ * This implementation avoids d8-d15 because they are callee-save in user
+ * space.
+ *
+ * void __arch_chacha20_blocks_nostack(uint8_t *dst_bytes,
+ *				       const uint8_t *key,
+ * 				       uint32_t *counter,
+ *				       size_t nblocks)
+ *
+ * 	x0: output bytes
+ *	x1: 32-byte key input
+ *	x2: 8-byte counter input/output
+ *	x3: number of 64-byte block to write to output
+ */
+SYM_FUNC_START(__arch_chacha20_blocks_nostack)
+
+	/* copy0 = "expand 32-byte k" */
+	mov_q		x8, 0x3320646e61707865
+	mov_q		x9, 0x6b20657479622d32
+	mov		copy0.d[0], x8
+	mov		copy0.d[1], x9
+
+	/* copy1,copy2 = key */
+	ld1		{ copy1.4s, copy2.4s }, [x1]
+	/* copy3 = counter || zero nonce  */
+	ld1		{ copy3.2s }, [x2]
+
+	movi		one_v.2s, #1
+	uzp1		one_v.4s, one_v.4s, one_v.4s
+
+.Lblock:
+	/* copy state to auxiliary vectors for the final add after the permute.  */
+	mov		state0.16b, copy0.16b
+	mov		state1.16b, copy1.16b
+	mov		state2.16b, copy2.16b
+	mov		state3.16b, copy3.16b
+
+	mov		w4, 20
+.Lpermute:
+	/*
+	 * Permute one 64-byte block where the state matrix is stored in the four NEON
+	 * registers state0-state3.  It performs matrix operations on four words in parallel,
+	 * but requires shuffling to rearrange the words after each round.
+	 */
+
+.Ldoubleround:
+	/* state0 += state1, state3 = rotl32(state3 ^ state0, 16) */
+	add		state0.4s, state0.4s, state1.4s
+	eor		state3.16b, state3.16b, state0.16b
+	rev32		state3.8h, state3.8h
+
+	/* state2 += state3, state1 = rotl32(state1 ^ state2, 12) */
+	add		state2.4s, state2.4s, state3.4s
+	eor		tmp.16b, state1.16b, state2.16b
+	shl		state1.4s, tmp.4s, #12
+	sri		state1.4s, tmp.4s, #20
+
+	/* state0 += state1, state3 = rotl32(state3 ^ state0, 8) */
+	add		state0.4s, state0.4s, state1.4s
+	eor		tmp.16b, state3.16b, state0.16b
+	shl		state3.4s, tmp.4s, #8
+	sri		state3.4s, tmp.4s, #24
+
+	/* state2 += state3, state1 = rotl32(state1 ^ state2, 7) */
+	add		state2.4s, state2.4s, state3.4s
+	eor		tmp.16b, state1.16b, state2.16b
+	shl		state1.4s, tmp.4s, #7
+	sri		state1.4s, tmp.4s, #25
+
+	/* state1[0,1,2,3] = state1[1,2,3,0] */
+	ext		state1.16b, state1.16b, state1.16b, #4
+	/* state2[0,1,2,3] = state2[2,3,0,1] */
+	ext		state2.16b, state2.16b, state2.16b, #8
+	/* state3[0,1,2,3] = state3[1,2,3,0] */
+	ext		state3.16b, state3.16b, state3.16b, #12
+
+	/* state0 += state1, state3 = rotl32(state3 ^ state0, 16) */
+	add		state0.4s, state0.4s, state1.4s
+	eor		state3.16b, state3.16b, state0.16b
+	rev32		state3.8h, state3.8h
+
+	/* state2 += state3, state1 = rotl32(state1 ^ state2, 12) */
+	add		state2.4s, state2.4s, state3.4s
+	eor		tmp.16b, state1.16b, state2.16b
+	shl		state1.4s, tmp.4s, #12
+	sri		state1.4s, tmp.4s, #20
+
+	/* state0 += state1, state3 = rotl32(state3 ^ state0, 8) */
+	add		state0.4s, state0.4s, state1.4s
+	eor		tmp.16b, state3.16b, state0.16b
+	shl		state3.4s, tmp.4s, #8
+	sri		state3.4s, tmp.4s, #24
+
+	/* state2 += state3, state1 = rotl32(state1 ^ state2, 7) */
+	add		state2.4s, state2.4s, state3.4s
+	eor		tmp.16b, state1.16b, state2.16b
+	shl		state1.4s, tmp.4s, #7
+	sri		state1.4s, tmp.4s, #25
+
+	/* state1[0,1,2,3] = state1[3,0,1,2] */
+	ext		state1.16b, state1.16b, state1.16b, #12
+	/* state2[0,1,2,3] = state2[2,3,0,1] */
+	ext		state2.16b, state2.16b, state2.16b, #8
+	/* state3[0,1,2,3] = state3[1,2,3,0] */
+	ext		state3.16b, state3.16b, state3.16b, #4
+
+	subs		w4, w4, #2
+	b.ne		.Ldoubleround
+
+	/* output0 = state0 + state0 */
+	add		state0.4s, state0.4s, copy0.4s
+	/* output1 = state1 + state1 */
+	add		state1.4s, state1.4s, copy1.4s
+	/* output2 = state2 + state2 */
+	add		state2.4s, state2.4s, copy2.4s
+	/* output2 = state3 + state3 */
+	add		state3.4s, state3.4s, copy3.4s
+	st1		{ state0.16b - state3.16b }, [x0]
+
+	/*
+	 * ++copy3.counter, the 'add' clears the upper half of the SIMD register
+	 * which is the expected behaviour here.
+	 */
+	add		copy3_d, copy3_d, one_d
+
+	/* output += 64, --nblocks */
+	add		x0, x0, 64
+	subs		x3, x3, #1
+	b.ne		.Lblock
+
+	/* counter = copy3.counter */
+	st1		{ copy3.2s }, [x2]
+
+	/* Zero out the potentially sensitive regs, in case nothing uses these again. */
+	movi		state0.16b, #0
+	movi		state1.16b, #0
+	movi		state2.16b, #0
+	movi		state3.16b, #0
+	movi		copy1.16b, #0
+	movi		copy2.16b, #0
+	ret
+SYM_FUNC_END(__arch_chacha20_blocks_nostack)
+
+emit_aarch64_feature_1_and

arch/arm64/kernel/vdso/vgetrandom.c

+// SPDX-License-Identifier: GPL-2.0
+
+#include <uapi/asm-generic/errno.h>
+
+typeof(__cvdso_getrandom) __kernel_getrandom;
+
+ssize_t __kernel_getrandom(void *buffer, size_t len, unsigned int flags, void *opaque_state, size_t opaque_len)
+{
+	if (alternative_has_cap_likely(ARM64_HAS_FPSIMD))
+		return __cvdso_getrandom(buffer, len, flags, opaque_state, opaque_len);
+
+	if (unlikely(opaque_len == ~0UL && !buffer && !len && !flags))
+		return -ENOSYS;
+	return getrandom_syscall(buffer, len, flags);
+}

tools/arch/arm64/vdso

+../../../arch/arm64/kernel/vdso
\ No newline at end of file

tools/include/linux/compiler.h

@@ -2,6 +2,8 @@
 #ifndef _TOOLS_LINUX_COMPILER_H_
 #define _TOOLS_LINUX_COMPILER_H_
 
+#ifndef __ASSEMBLY__
+
 #include <linux/compiler_types.h>
 
 #ifndef __compiletime_error
@@ -224,4 +226,6 @@ static __always_inline void __write_once_size(volatile void *p, void *res, int s
 	__asm__ ("" : "=r" (var) : "0" (var))
 #endif
 
+#endif /* __ASSEMBLY__ */
+
 #endif /* _TOOLS_LINUX_COMPILER_H */

tools/testing/selftests/vDSO/Makefile

@@ -9,7 +9,7 @@ ifeq ($(ARCH),$(filter $(ARCH),x86 x86_64))
 TEST_GEN_PROGS += vdso_standalone_test_x86
 endif
 TEST_GEN_PROGS += vdso_test_correctness
-ifeq ($(ARCH)$(CONFIG_X86_32),$(filter $(ARCH)$(CONFIG_X86_32),x86 x86_64 loongarch))
+ifeq ($(ARCH)$(CONFIG_X86_32),$(filter $(ARCH)$(CONFIG_X86_32),x86 x86_64 loongarch arm64))
 TEST_GEN_PROGS += vdso_test_getrandom
 TEST_GEN_PROGS += vdso_test_chacha
 endif
@@ -40,5 +40,6 @@ $(OUTPUT)/vdso_test_getrandom: CFLAGS += -isystem $(top_srcdir)/tools/include \
 $(OUTPUT)/vdso_test_chacha: $(top_srcdir)/tools/arch/$(SRCARCH)/vdso/vgetrandom-chacha.S
 $(OUTPUT)/vdso_test_chacha: CFLAGS += -idirafter $(top_srcdir)/tools/include \
                                       -idirafter $(top_srcdir)/arch/$(SRCARCH)/include \
+                                      -idirafter $(top_srcdir)/arch/$(SRCARCH)/include/generated \
                                       -idirafter $(top_srcdir)/include \
                                       -D__ASSEMBLY__ -Wa,--noexecstack