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

Signed-off-by: Adhemerval Zanella <adhemerval.zanella@linaro.org>

--

Changes from v2:
- Refactor Makefile to use same flags for vgettimeofday and
  vgetrandom.
- Removed rodata usage and fixed BE on vgetrandom-chacha.S.

Changes from v1:
- Fixed style issues and typos.
- Added fallback for systems without NEON support.
- Avoid use of non-volatile vector registers in neon chacha20.
- Use c-getrandom-y for vgetrandom.c.
- Fixed TIMENS vdso_rnd_data access.
---
 arch/arm64/Kconfig                         |   1 +
 arch/arm64/include/asm/vdso.h              |   6 +
 arch/arm64/include/asm/vdso/getrandom.h    |  49 ++++++
 arch/arm64/include/asm/vdso/vsyscall.h     |  10 ++
 arch/arm64/kernel/vdso.c                   |   6 -
 arch/arm64/kernel/vdso/Makefile            |  25 ++-
 arch/arm64/kernel/vdso/vdso                |   1 +
 arch/arm64/kernel/vdso/vdso.lds.S          |   4 +
 arch/arm64/kernel/vdso/vgetrandom-chacha.S | 178 +++++++++++++++++++++
 arch/arm64/kernel/vdso/vgetrandom.c        |  15 ++
 lib/vdso/getrandom.c                       |   1 +
 tools/arch/arm64/vdso                      |   1 +
 tools/include/linux/compiler.h             |   4 +
 tools/testing/selftests/vDSO/Makefile      |   3 +-
 14 files changed, 289 insertions(+), 15 deletions(-)
 create mode 100644 arch/arm64/include/asm/vdso/getrandom.h
 create mode 120000 arch/arm64/kernel/vdso/vdso
 create mode 100644 arch/arm64/kernel/vdso/vgetrandom-chacha.S
 create mode 100644 arch/arm64/kernel/vdso/vgetrandom.c
 create mode 120000 tools/arch/arm64/vdso

diff --git a/arch/arm64/Kconfig b/arch/arm64/Kconfig
index a2f8ff354ca6..7f7424d1b3b8 100644
--- a/arch/arm64/Kconfig
+++ b/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.
 
diff --git a/arch/arm64/include/asm/vdso.h b/arch/arm64/include/asm/vdso.h
index 4305995c8f82..18407b757c95 100644
--- a/arch/arm64/include/asm/vdso.h
+++ b/arch/arm64/include/asm/vdso.h
@@ -16,6 +16,12 @@
 
 #ifndef __ASSEMBLY__
 
+enum vvar_pages {
+	VVAR_DATA_PAGE_OFFSET,
+	VVAR_TIMENS_PAGE_OFFSET,
+	VVAR_NR_PAGES,
+};
+
 #include <generated/vdso-offsets.h>
 
 #define VDSO_SYMBOL(base, name)						   \
diff --git a/arch/arm64/include/asm/vdso/getrandom.h b/arch/arm64/include/asm/vdso/getrandom.h
new file mode 100644
index 000000000000..44b6739be821
--- /dev/null
+++ b/arch/arm64/include/asm/vdso/getrandom.h
@@ -0,0 +1,49 @@
+/* SPDX-License-Identifier: GPL-2.0 */
+
+#ifndef __ASM_VDSO_GETRANDOM_H
+#define __ASM_VDSO_GETRANDOM_H
+
+#ifndef __ASSEMBLY__
+
+#include <asm/vdso.h>
+#include <asm/unistd.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)
+{
+	/*
+	 * If a task belongs to a time namespace then the real VVAR page is mapped
+	 * with the VVAR_TIMENS_PAGE_OFFSET offset.
+	 */
+	if (IS_ENABLED(CONFIG_TIME_NS) && _vdso_data->clock_mode == VDSO_CLOCKMODE_TIMENS)
+		return (void*)&_vdso_rng_data + VVAR_TIMENS_PAGE_OFFSET * PAGE_SIZE;
+	return &_vdso_rng_data;
+}
+
+#endif /* !__ASSEMBLY__ */
+
+#endif /* __ASM_VDSO_GETRANDOM_H */
diff --git a/arch/arm64/include/asm/vdso/vsyscall.h b/arch/arm64/include/asm/vdso/vsyscall.h
index f94b1457c117..2a87f0e1b144 100644
--- a/arch/arm64/include/asm/vdso/vsyscall.h
+++ b/arch/arm64/include/asm/vdso/vsyscall.h
@@ -2,8 +2,11 @@
 #ifndef __ASM_VDSO_VSYSCALL_H
 #define __ASM_VDSO_VSYSCALL_H
 
+#define __VDSO_RND_DATA_OFFSET  480
+
 #ifndef __ASSEMBLY__
 
+#include <asm/vdso.h>
 #include <linux/timekeeper_internal.h>
 #include <vdso/datapage.h>
 
@@ -21,6 +24,13 @@ 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)
 {
diff --git a/arch/arm64/kernel/vdso.c b/arch/arm64/kernel/vdso.c
index 89b6e7840002..706c9c3a7a50 100644
--- a/arch/arm64/kernel/vdso.c
+++ b/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;
diff --git a/arch/arm64/kernel/vdso/Makefile b/arch/arm64/kernel/vdso/Makefile
index d11da6461278..35685c036044 100644
--- a/arch/arm64/kernel/vdso/Makefile
+++ b/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) \
-				$(RANDSTRUCT_CFLAGS) $(GCC_PLUGINS_CFLAGS) \
-				$(CC_FLAGS_LTO) $(CC_FLAGS_CFI) \
-				-Wmissing-prototypes -Wmissing-declarations
+# 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)
 
diff --git a/arch/arm64/kernel/vdso/vdso b/arch/arm64/kernel/vdso/vdso
new file mode 120000
index 000000000000..233c7a26f6e5
--- /dev/null
+++ b/arch/arm64/kernel/vdso/vdso
@@ -0,0 +1 @@
+../../../arch/arm64/kernel/vdso
\ No newline at end of file
diff --git a/arch/arm64/kernel/vdso/vdso.lds.S b/arch/arm64/kernel/vdso/vdso.lds.S
index 45354f2ddf70..f204a9ddc833 100644
--- a/arch/arm64/kernel/vdso/vdso.lds.S
+++ b/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: *;
 	};
 }
diff --git a/arch/arm64/kernel/vdso/vgetrandom-chacha.S b/arch/arm64/kernel/vdso/vgetrandom-chacha.S
new file mode 100644
index 000000000000..4e5f9c349522
--- /dev/null
+++ b/arch/arm64/kernel/vdso/vgetrandom-chacha.S
@@ -0,0 +1,178 @@
+// 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  */
+	ldr		copy3_d, [x2]
+CPU_BE( rev64		copy3.4s, copy3.4s)
+
+	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
+CPU_BE( rev32		state0.16b, state0.16b)
+	/* output1 = state1 + state1 */
+	add		state1.4s, state1.4s, copy1.4s
+CPU_BE( rev32		state1.16b, state1.16b)
+	/* output2 = state2 + state2 */
+	add		state2.4s, state2.4s, copy2.4s
+CPU_BE( rev32		state2.16b, state2.16b)
+	/* output2 = state3 + state3 */
+	add		state3.4s, state3.4s, copy3.4s
+CPU_BE( rev32		state3.16b, state3.16b)
+	st1		{ state0.4s - state3.4s }, [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 */
+CPU_BE( rev64		copy3.4s, copy3.4s)
+	str		copy3_d, [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
diff --git a/arch/arm64/kernel/vdso/vgetrandom.c b/arch/arm64/kernel/vdso/vgetrandom.c
new file mode 100644
index 000000000000..95682d29c4bf
--- /dev/null
+++ b/arch/arm64/kernel/vdso/vgetrandom.c
@@ -0,0 +1,15 @@
+// SPDX-License-Identifier: GPL-2.0
+
+typeof(__cvdso_getrandom) __kernel_getrandom;
+
+ssize_t __kernel_getrandom(void *buffer, size_t len, unsigned int flags, void *opaque_state, size_t opaque_len)
+{
+	asm goto (
+	ALTERNATIVE("b %[fallback]", "nop", ARM64_HAS_FPSIMD) : : : : fallback);
+	return __cvdso_getrandom(buffer, len, flags, opaque_state, opaque_len);
+
+fallback:
+	if (unlikely(opaque_len == ~0UL && !buffer && !len && !flags))
+		return -ENOSYS;
+	return getrandom_syscall(buffer, len, flags);
+}
diff --git a/lib/vdso/getrandom.c b/lib/vdso/getrandom.c
index 938ca539aaa6..7c9711248d9b 100644
--- a/lib/vdso/getrandom.c
+++ b/lib/vdso/getrandom.c
@@ -5,6 +5,7 @@
 
 #include <linux/array_size.h>
 #include <linux/minmax.h>
+#include <linux/mm.h>
 #include <vdso/datapage.h>
 #include <vdso/getrandom.h>
 #include <vdso/unaligned.h>
diff --git a/tools/arch/arm64/vdso b/tools/arch/arm64/vdso
new file mode 120000
index 000000000000..233c7a26f6e5
--- /dev/null
+++ b/tools/arch/arm64/vdso
@@ -0,0 +1 @@
+../../../arch/arm64/kernel/vdso
\ No newline at end of file
diff --git a/tools/include/linux/compiler.h b/tools/include/linux/compiler.h
index 6f7f22ac9da5..4366da278033 100644
--- a/tools/include/linux/compiler.h
+++ b/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 */
diff --git a/tools/testing/selftests/vDSO/Makefile b/tools/testing/selftests/vDSO/Makefile
index 04930125035e..3c6fafbd83a6 100644
--- a/tools/testing/selftests/vDSO/Makefile
+++ b/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
-- 
2.43.0

On Mon, Sep 02, 2024 at 12:52:57PM +0000, Adhemerval Zanella wrote:
> +static __always_inline const struct vdso_rng_data *__arch_get_vdso_rng_data(void)
> +{
> +	/*
> +	 * If a task belongs to a time namespace then the real VVAR page is mapped
> +	 * with the VVAR_TIMENS_PAGE_OFFSET offset.
> +	 */

This confused me, and I see that it is truncated from the existing
commit in arch/arm64/kerne/vdso.c:

	If a task belongs to a time namespace then a namespace specific VVAR is
	mapped with the VVAR_DATA_PAGE_OFFSET and the real VVAR page is mapped
	with the VVAR_TIMENS_PAGE_OFFSET offset.

... and IIUC the "namespace specific VVAR" page doesn't have the RNG
data, right? It'd be good to spell that out, e.g.

	/*
	 * The RNG data is in the real VVAR data page, but if a task
	 * belongs to a time namespsace then VVAR_DATA_PAGE_OFFSET
	 * points to the namespace-specific VVAR page and
	 * VVAR_TIMENS_PAGE_OFFSET points to the real VVAR page.
	 */

It does feel weird that everything else has to work around timer
namespaces rather than that being limited to the timer code, so we'll
probably want to flip that if we add anything else to the VDSO, or have
a separate VVAR_RNG page.

> +	if (IS_ENABLED(CONFIG_TIME_NS) && _vdso_data->clock_mode == VDSO_CLOCKMODE_TIMENS)
> +		return (void*)&_vdso_rng_data + VVAR_TIMENS_PAGE_OFFSET * PAGE_SIZE;
> +	return &_vdso_rng_data;
> +}

[...]

> diff --git a/arch/arm64/kernel/vdso/vgetrandom.c b/arch/arm64/kernel/vdso/vgetrandom.c
> new file mode 100644
> index 000000000000..95682d29c4bf
> --- /dev/null
> +++ b/arch/arm64/kernel/vdso/vgetrandom.c
> @@ -0,0 +1,15 @@
> +// SPDX-License-Identifier: GPL-2.0
> +
> +typeof(__cvdso_getrandom) __kernel_getrandom;
> +
> +ssize_t __kernel_getrandom(void *buffer, size_t len, unsigned int flags, void *opaque_state, size_t opaque_len)
> +{
> +	asm goto (
> +	ALTERNATIVE("b %[fallback]", "nop", ARM64_HAS_FPSIMD) : : : : fallback);
> +	return __cvdso_getrandom(buffer, len, flags, opaque_state, opaque_len);
> +
> +fallback:
> +	if (unlikely(opaque_len == ~0UL && !buffer && !len && !flags))
> +		return -ENOSYS;
> +	return getrandom_syscall(buffer, len, flags);
> +}

The asm it pretty painful to read, and AFAICT what you actually want
here is alternative_has_cap_likely(), which we could use were that not
using alt_cb_patch_nops behind the scenes.

I reckon it's worth making the work for the VDSO first (patch below);
that way you can make this much nicer:

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);
}

... though the conditions for returning -ENOSYS look very odd to me; why
do we care about fast-pathing that specific case rather than forwarding
that to the kernel, and does __cvdso_getrandom() handle that correctly?

Mark

---->8----
From b7ee23e4ec47805527c9d7c2ee6b02328fe8437a Mon Sep 17 00:00:00 2001
From: Mark Rutland <mark.rutland@arm.com>
Date: Mon, 2 Sep 2024 15:08:12 +0100
Subject: [PATCH] arm64: alternative: make alternative_has_cap_likely() VDSO
 compatible

Currently alternative_has_cap_unlikely() can be used in VDSO code, but
alternative_has_cap_likely() cannot as it references alt_cb_patch_nops,
which is not available when linking the VDSO. This is unfortunate as it
would be useful to have alternative_has_cap_likely() available in VDSO
code.

The use of alt_cb_patch_nops was added in commit:

  d926079f17bf8aa4 ("arm64: alternatives: add shared NOP callback")

... as removing duplicate NOPs within the kernel Image saved areasonable
amount of space.

Given the VDSO code will have nowhere near as many alternative branches
as the main kernel image, this isn't much of a concern, and a few extra
nops isn't a massive problem.

Change alternative_has_cap_likely() to only use alt_cb_patch_nops for
the main kernel image, and allow duplicate NOPs in VDSO code.

Signed-off-by: Mark Rutland <mark.rutland@arm.com>
Cc: Catalin Marinas <catalin.marinas@arm.com>
Cc: Will Deacon <will@kernel.org>
---
 arch/arm64/include/asm/alternative-macros.h | 4 ++++
 1 file changed, 4 insertions(+)

diff --git a/arch/arm64/include/asm/alternative-macros.h b/arch/arm64/include/asm/alternative-macros.h
index d328f549b1a60..c8c77f9e36d60 100644
--- a/arch/arm64/include/asm/alternative-macros.h
+++ b/arch/arm64/include/asm/alternative-macros.h
@@ -230,7 +230,11 @@ alternative_has_cap_likely(const unsigned long cpucap)
 		return false;
 
 	asm goto(
+#ifdef BUILD_VDSO
+	ALTERNATIVE("b	%l[l_no]", "nop", %[cpucap])
+#else
 	ALTERNATIVE_CB("b	%l[l_no]", %[cpucap], alt_cb_patch_nops)
+#endif
 	:
 	: [cpucap] "i" (cpucap)
 	:
-- 
2.30.2

On Mon, Sep 02, 2024 at 03:31:43PM +0100, Mark Rutland wrote:
> 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);
> }
> 
> ... though the conditions for returning -ENOSYS look very odd to me; why
> do we care about fast-pathing that specific case rather than forwarding
> that to the kernel, and does __cvdso_getrandom() handle that correctly?

Adhemerval's code here is fine and correct. The opaque_len==~0UL thing
is a special vDSO case for getting the param struct back, not something
related to the kernel. See __cvdso_getrandom_data() for details.

On Mon, Sep 02, 2024 at 04:41:28PM +0200, Jason A. Donenfeld wrote:
> On Mon, Sep 02, 2024 at 03:31:43PM +0100, Mark Rutland wrote:
> > 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);
> > }
> > 
> > ... though the conditions for returning -ENOSYS look very odd to me; why
> > do we care about fast-pathing that specific case rather than forwarding
> > that to the kernel, and does __cvdso_getrandom() handle that correctly?
> 
> Adhemerval's code here is fine and correct. The opaque_len==~0UL thing
> is a special vDSO case for getting the param struct back, not something
> related to the kernel. See __cvdso_getrandom_data() for details.

Ok, so this is to say "we cannot provide a vgetrandom_opaque_params".

Is the syscall fallback just for the CRIU case mentioned in
__cvdso_getrandom_data()? The comment above __cvdso_getrandom_data()
says:

  If @buffer, @len, and @flags are 0, and @opaque_len is ~0UL, then
  @opaque_state is populated with a struct vgetrandom_opaque_params and the
  function returns 0; if it does not return 0, this function should not be
  used.

... so presumably the caller shouldn't bother to call again if it got
-ENOSYS above.

Mark.