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Message-ID: <20200902170854.GK6642@arm.com>
Date: Wed, 2 Sep 2020 18:08:54 +0100
From: Dave Martin <Dave.Martin@....com>
To: Boyan Karatotev <boyan.karatotev@....com>
Cc: linux-arm-kernel@...ts.infradead.org,
linux-kselftest@...r.kernel.org, linux-kernel@...r.kernel.org,
Will Deacon <will@...nel.org>, boian4o1@...il.com,
Catalin Marinas <catalin.marinas@....com>,
amit.kachhap@....com, vincenzo.frascino@....com,
Shuah Khan <shuah@...nel.org>
Subject: Re: [PATCH v2 3/4] kselftests/arm64: add PAuth test for whether
exec() changes keys
On Mon, Aug 31, 2020 at 12:04:49PM +0100, Boyan Karatotev wrote:
> Kernel documentation states that it will change PAuth keys on exec() calls.
>
> Verify that all keys are correctly switched to new ones.
>
> Cc: Shuah Khan <shuah@...nel.org>
> Cc: Catalin Marinas <catalin.marinas@....com>
> Cc: Will Deacon <will@...nel.org>
> Reviewed-by: Vincenzo Frascino <Vincenzo.Frascino@....com>
> Reviewed-by: Amit Daniel Kachhap <amit.kachhap@....com>
> Signed-off-by: Boyan Karatotev <boyan.karatotev@....com>
> ---
> tools/testing/selftests/arm64/pauth/Makefile | 4 +
> .../selftests/arm64/pauth/exec_target.c | 35 +++++
> tools/testing/selftests/arm64/pauth/helper.h | 10 ++
> tools/testing/selftests/arm64/pauth/pac.c | 148 ++++++++++++++++++
> 4 files changed, 197 insertions(+)
> create mode 100644 tools/testing/selftests/arm64/pauth/exec_target.c
>
> diff --git a/tools/testing/selftests/arm64/pauth/Makefile b/tools/testing/selftests/arm64/pauth/Makefile
> index 5c0dd129562f..72e290b0b10c 100644
> --- a/tools/testing/selftests/arm64/pauth/Makefile
> +++ b/tools/testing/selftests/arm64/pauth/Makefile
> @@ -13,6 +13,7 @@ pauth_cc_support := $(shell if ($(CC) $(CFLAGS) -march=armv8.3-a -E -x c /dev/nu
> ifeq ($(pauth_cc_support),1)
> TEST_GEN_PROGS := pac
> TEST_GEN_FILES := pac_corruptor.o helper.o
> +TEST_GEN_PROGS_EXTENDED := exec_target
> endif
>
> include ../../lib.mk
> @@ -30,6 +31,9 @@ $(OUTPUT)/helper.o: helper.c
> # greater, gcc emits pac* instructions which are not in HINT NOP space,
> # preventing the tests from occurring at all. Compile for ARMv8.2 so tests can
> # run on earlier targets and print a meaningful error messages
> +$(OUTPUT)/exec_target: exec_target.c $(OUTPUT)/helper.o
> + $(CC) $^ -o $@ $(CFLAGS) -march=armv8.2-a
> +
> $(OUTPUT)/pac: pac.c $(OUTPUT)/pac_corruptor.o $(OUTPUT)/helper.o
> $(CC) $^ -o $@ $(CFLAGS) -march=armv8.2-a
> endif
> diff --git a/tools/testing/selftests/arm64/pauth/exec_target.c b/tools/testing/selftests/arm64/pauth/exec_target.c
> new file mode 100644
> index 000000000000..07addef5a1d7
> --- /dev/null
> +++ b/tools/testing/selftests/arm64/pauth/exec_target.c
> @@ -0,0 +1,35 @@
> +// SPDX-License-Identifier: GPL-2.0
> +// Copyright (C) 2020 ARM Limited
> +
> +#include <stdio.h>
> +#include <stdlib.h>
> +#include <sys/auxv.h>
> +
> +#include "helper.h"
> +
> +
> +int main(void)
> +{
> + struct signatures signed_vals;
> + unsigned long hwcaps;
> + size_t val;
> +
> + fread(&val, sizeof(size_t), 1, stdin);
> +
> + /* don't try to execute illegal (unimplemented) instructions) caller
> + * should have checked this and keep worker simple
> + */
> + hwcaps = getauxval(AT_HWCAP);
> +
> + if (hwcaps & HWCAP_PACA) {
> + signed_vals.keyia = keyia_sign(val);
> + signed_vals.keyib = keyib_sign(val);
> + signed_vals.keyda = keyda_sign(val);
> + signed_vals.keydb = keydb_sign(val);
> + }
> + signed_vals.keyg = (hwcaps & HWCAP_PACG) ? keyg_sign(val) : 0;
> +
> + fwrite(&signed_vals, sizeof(struct signatures), 1, stdout);
> +
> + return 0;
> +}
> diff --git a/tools/testing/selftests/arm64/pauth/helper.h b/tools/testing/selftests/arm64/pauth/helper.h
> index e2ed910c9863..da6457177727 100644
> --- a/tools/testing/selftests/arm64/pauth/helper.h
> +++ b/tools/testing/selftests/arm64/pauth/helper.h
> @@ -6,6 +6,16 @@
>
> #include <stdlib.h>
>
> +#define NKEYS 5
> +
> +
> +struct signatures {
> + size_t keyia;
> + size_t keyib;
> + size_t keyda;
> + size_t keydb;
> + size_t keyg;
> +};
>
> void pac_corruptor(void);
>
> diff --git a/tools/testing/selftests/arm64/pauth/pac.c b/tools/testing/selftests/arm64/pauth/pac.c
> index 035fdd6aae9b..1b9e3acfeb61 100644
> --- a/tools/testing/selftests/arm64/pauth/pac.c
> +++ b/tools/testing/selftests/arm64/pauth/pac.c
> @@ -2,6 +2,8 @@
> // Copyright (C) 2020 ARM Limited
>
> #include <sys/auxv.h>
> +#include <sys/types.h>
> +#include <sys/wait.h>
> #include <signal.h>
>
> #include "../../kselftest_harness.h"
> @@ -33,6 +35,117 @@ do { \
> } while (0)
>
>
> +void sign_specific(struct signatures *sign, size_t val)
> +{
> + sign->keyia = keyia_sign(val);
> + sign->keyib = keyib_sign(val);
> + sign->keyda = keyda_sign(val);
> + sign->keydb = keydb_sign(val);
> +}
> +
> +void sign_all(struct signatures *sign, size_t val)
> +{
> + sign->keyia = keyia_sign(val);
> + sign->keyib = keyib_sign(val);
> + sign->keyda = keyda_sign(val);
> + sign->keydb = keydb_sign(val);
> + sign->keyg = keyg_sign(val);
> +}
> +
> +int are_same(struct signatures *old, struct signatures *new, int nkeys)
> +{
> + int res = 0;
> +
> + res |= old->keyia == new->keyia;
> + res |= old->keyib == new->keyib;
> + res |= old->keyda == new->keyda;
> + res |= old->keydb == new->keydb;
> + if (nkeys == NKEYS)
> + res |= old->keyg == new->keyg;
> +
> + return res;
> +}
> +
> +int exec_sign_all(struct signatures *signed_vals, size_t val)
> +{
> + int new_stdin[2];
> + int new_stdout[2];
> + int status;
> + ssize_t ret;
> + pid_t pid;
Can we simplify this with popen(3)? Fork-and-exec is notoriously
fiddly...
[...]
> +/*
> + * fork() does not change keys. Only exec() does so call a worker program.
> + * Its only job is to sign a value and report back the resutls
> + */
> +TEST(exec_unique_keys)
> +{
The kernel doesn't guarantee that keys are unique.
Can we present all the "unique keys" wording differently, say
exec_key_collision_likely()
Otherwise people might infer from this test code that the keys are
supposed to be truly unique and start reporting bugs on the kernel.
I can't see an obvious security argument for unique keys (rather, the
keys just need to be "unique enough". That's the job of
get_random_bytes().)
[...]
Cheers
---Dave
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