On 8/28/20 2:16 PM, Boyan Karatotev wrote:
> PAuth signs and verifies return addresses on the stack. It does so by
> inserting a Pointer Authentication code (PAC) into some of the unused top
> bits of an address. This is achieved by adding paciasp/autiasp instructions
> at the beginning and end of a function.
>
> This feature is partially backwards compatible with earlier versions of the
> ARM architecture. To coerce the compiler into emitting fully backwards
> compatible code the main file is compiled to target an earlier ARM version.
> This allows the tests to check for the feature and print meaningful error
> messages instead of crashing.
>
> Add a test to verify that corrupting the return address results in a
> SIGSEGV on return.
>
Reviewed-by: Vincenzo Frascino <Vincenzo.Frascino@xxxxxxx>
> Cc: Shuah Khan <shuah@xxxxxxxxxx>
> Cc: Catalin Marinas <catalin.marinas@xxxxxxx>
> Cc: Will Deacon <will@xxxxxxxxxx>
> Signed-off-by: Boyan Karatotev <boyan.karatotev@xxxxxxx>
> ---
> tools/testing/selftests/arm64/Makefile | 2 +-
> .../testing/selftests/arm64/pauth/.gitignore | 1 +
> tools/testing/selftests/arm64/pauth/Makefile | 22 ++++++++++++
> tools/testing/selftests/arm64/pauth/helper.h | 10 ++++++
> tools/testing/selftests/arm64/pauth/pac.c | 32 +++++++++++++++++
> .../selftests/arm64/pauth/pac_corruptor.S | 36 +++++++++++++++++++
> 6 files changed, 102 insertions(+), 1 deletion(-)
> create mode 100644 tools/testing/selftests/arm64/pauth/.gitignore
> create mode 100644 tools/testing/selftests/arm64/pauth/Makefile
> create mode 100644 tools/testing/selftests/arm64/pauth/helper.h
> create mode 100644 tools/testing/selftests/arm64/pauth/pac.c
> create mode 100644 tools/testing/selftests/arm64/pauth/pac_corruptor.S
>
> diff --git a/tools/testing/selftests/arm64/Makefile b/tools/testing/selftests/arm64/Makefile
> index 93b567d23c8b..525506fd97b9 100644
> --- a/tools/testing/selftests/arm64/Makefile
> +++ b/tools/testing/selftests/arm64/Makefile
> @@ -4,7 +4,7 @@
> ARCH ?= $(shell uname -m 2>/dev/null || echo not)
>
> ifneq (,$(filter $(ARCH),aarch64 arm64))
> -ARM64_SUBTARGETS ?= tags signal
> +ARM64_SUBTARGETS ?= tags signal pauth
> else
> ARM64_SUBTARGETS :=
> endif
> diff --git a/tools/testing/selftests/arm64/pauth/.gitignore b/tools/testing/selftests/arm64/pauth/.gitignore
> new file mode 100644
> index 000000000000..b557c916720a
> --- /dev/null
> +++ b/tools/testing/selftests/arm64/pauth/.gitignore
> @@ -0,0 +1 @@
> +pac
> diff --git a/tools/testing/selftests/arm64/pauth/Makefile b/tools/testing/selftests/arm64/pauth/Makefile
> new file mode 100644
> index 000000000000..785c775e5e41
> --- /dev/null
> +++ b/tools/testing/selftests/arm64/pauth/Makefile
> @@ -0,0 +1,22 @@
> +# SPDX-License-Identifier: GPL-2.0
> +# Copyright (C) 2020 ARM Limited
> +
> +CFLAGS += -mbranch-protection=pac-ret
> +
> +TEST_GEN_PROGS := pac
> +TEST_GEN_FILES := pac_corruptor.o
> +
> +include ../../lib.mk
> +
> +# pac* and aut* instructions are not available on architectures berfore
> +# ARMv8.3. Therefore target ARMv8.3 wherever they are used directly
> +$(OUTPUT)/pac_corruptor.o: pac_corruptor.S
> + $(CC) -c $^ -o $@ $(CFLAGS) -march=armv8.3-a
> +
> +# when -mbranch-protection is enabled and the target architecture is ARMv8.3 or
> +# greater, gcc emits pac* instructions which are not in HINT NOP space,
> +# preventing the tests from occurring at all. Compile for ARMv8.2 so tests can
> +# run on earlier targets and print a meaningful error messages
> +$(OUTPUT)/pac: pac.c $(OUTPUT)/pac_corruptor.o
> + $(CC) $^ -o $@ $(CFLAGS) -march=armv8.2-a
> +
> diff --git a/tools/testing/selftests/arm64/pauth/helper.h b/tools/testing/selftests/arm64/pauth/helper.h
> new file mode 100644
> index 000000000000..f777f88acf0a
> --- /dev/null
> +++ b/tools/testing/selftests/arm64/pauth/helper.h
> @@ -0,0 +1,10 @@
> +/* SPDX-License-Identifier: GPL-2.0 */
> +/* Copyright (C) 2020 ARM Limited */
> +
> +#ifndef _HELPER_H_
> +#define _HELPER_H_
> +
> +void pac_corruptor(void);
> +
> +#endif
> +
> diff --git a/tools/testing/selftests/arm64/pauth/pac.c b/tools/testing/selftests/arm64/pauth/pac.c
> new file mode 100644
> index 000000000000..ed445050f621
> --- /dev/null
> +++ b/tools/testing/selftests/arm64/pauth/pac.c
> @@ -0,0 +1,32 @@
> +// SPDX-License-Identifier: GPL-2.0
> +// Copyright (C) 2020 ARM Limited
> +
> +#include <sys/auxv.h>
> +#include <signal.h>
> +
> +#include "../../kselftest_harness.h"
> +#include "helper.h"
> +
> +/*
> + * Tests are ARMv8.3 compliant. They make no provisions for features present in
> + * future version of the arm architecture
> + */
> +
> +#define ASSERT_PAUTH_ENABLED() \
> +do { \
> + unsigned long hwcaps = getauxval(AT_HWCAP); \
> + /* data key instructions are not in NOP space. This prevents a SIGILL */ \
> + ASSERT_NE(0, hwcaps & HWCAP_PACA) TH_LOG("PAUTH not enabled"); \
> +} while (0)
> +
> +
> +/* check that a corrupted PAC results in SIGSEGV */
> +TEST_SIGNAL(corrupt_pac, SIGSEGV)
> +{
> + ASSERT_PAUTH_ENABLED();
> +
> + pac_corruptor();
> +}
> +
> +TEST_HARNESS_MAIN
> +
> diff --git a/tools/testing/selftests/arm64/pauth/pac_corruptor.S b/tools/testing/selftests/arm64/pauth/pac_corruptor.S
> new file mode 100644
> index 000000000000..6a34ec23a034
> --- /dev/null
> +++ b/tools/testing/selftests/arm64/pauth/pac_corruptor.S
> @@ -0,0 +1,36 @@
> +/* SPDX-License-Identifier: GPL-2.0 */
> +/* Copyright (C) 2020 ARM Limited */
> +
> +.global pac_corruptor
> +
> +.text
> +/*
> + * Corrupting a single bit of the PAC ensures the authentication will fail. It
> + * also guarantees no possible collision. TCR_EL1.TBI0 is set by default so no
> + * top byte PAC is tested
> + */
> + pac_corruptor:
> + paciasp
> +
> + /* make stack frame */
> + sub sp, sp, #16
> + stp x29, lr, [sp]
> + mov x29, sp
> +
> + /* prepare mask for bit to be corrupted (bit 54) */
> + mov x1, xzr
> + add x1, x1, #1
> + lsl x1, x1, #54
> +
> + /* get saved lr, corrupt selected bit, put it back */
> + ldr x0, [sp, #8]
> + eor x0, x0, x1
> + str x0, [sp, #8]
> +
> + /* remove stack frame */
> + ldp x29, lr, [sp]
> + add sp, sp, #16
> +
> + autiasp
> + ret
> +
>
--
Regards,
Vincenzo
