[PATCH v4 2/2] arm64: vdso: wire up getrandom() vDSO implementation

From: Adhemerval Zanella
Date: Mon Sep 02 2024 - 12:19:55 EST

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@xxxxxxxxxx>
---
arch/arm64/Kconfig | 1 +
arch/arm64/include/asm/mman.h | 6 +-
arch/arm64/include/asm/vdso.h | 6 +
arch/arm64/include/asm/vdso/getrandom.h | 50 ++++++
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 ++
tools/arch/arm64/vdso | 1 +
tools/include/linux/compiler.h | 4 +
tools/testing/selftests/vDSO/Makefile | 3 +-
14 files changed, 294 insertions(+), 16 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/mman.h b/arch/arm64/include/asm/mman.h
index 5966ee4a6154..ceb4370a69c5 100644
--- a/arch/arm64/include/asm/mman.h
+++ b/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__ */
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..6cda64e6da83
--- /dev/null
+++ b/arch/arm64/include/asm/vdso/getrandom.h
@@ -0,0 +1,50 @@
+/* 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)
+{
+ /*
+ * 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 */
diff --git a/arch/arm64/include/asm/vdso/vsyscall.h b/arch/arm64/include/asm/vdso/vsyscall.h
index f94b1457c117..b4241510dc36 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..832fe195292b
--- /dev/null
+++ b/arch/arm64/kernel/vdso/vgetrandom.c
@@ -0,0 +1,15 @@
+// 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);
+}
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