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Message-ID: <e7d078f7-c516-2055-bcae-d56de951b5d2@arm.com>
Date: Fri, 28 Aug 2020 15:33:55 +0100
From: Vincenzo Frascino <vincenzo.frascino@....com>
To: Boyan Karatotev <boyan.karatotev@....com>,
linux-arm-kernel@...ts.infradead.org,
linux-kselftest@...r.kernel.org, linux-kernel@...r.kernel.org
Cc: amit.kachhap@....com, boian4o1@...il.com,
Shuah Khan <shuah@...nel.org>,
Catalin Marinas <catalin.marinas@....com>,
Will Deacon <will@...nel.org>
Subject: Re: [PATCH 3/4] kselftests/arm64: add PAuth test for whether exec()
changes keys
On 8/28/20 2:16 PM, 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.
>
Reviewed-by: Vincenzo Frascino <Vincenzo.Frascino@....com>
> Cc: Shuah Khan <shuah@...nel.org>
> Cc: Catalin Marinas <catalin.marinas@....com>
> Cc: Will Deacon <will@...nel.org>
> 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 a017d1c8dd58..2e237b21ccf6 100644
> --- a/tools/testing/selftests/arm64/pauth/Makefile
> +++ b/tools/testing/selftests/arm64/pauth/Makefile
> @@ -5,6 +5,7 @@ CFLAGS += -mbranch-protection=pac-ret
>
> TEST_GEN_PROGS := pac
> TEST_GEN_FILES := pac_corruptor.o helper.o
> +TEST_GEN_PROGS_EXTENDED := exec_target
>
> include ../../lib.mk
>
> @@ -20,6 +21,9 @@ $(OUTPUT)/helper.o: helper.c
> # greater, gcc emits pac* instructions which are not in HINT NOP space,
> # preventing the tests from occurring at all. Compile for ARMv8.2 so tests can
> # run on earlier targets and print a meaningful error messages
> +$(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
>
> 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 b3cf709e249d..fceaa1e4824a 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 cdbffa8bf61e..16dea47b11c7 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;
> +
> + ret = pipe(new_stdin);
> + if (ret == -1) {
> + perror("pipe returned error");
> + return -1;
> + }
> +
> + ret = pipe(new_stdout);
> + if (ret == -1) {
> + perror("pipe returned error");
> + return -1;
> + }
> +
> + pid = fork();
> + // child
> + if (pid == 0) {
> + dup2(new_stdin[0], STDIN_FILENO);
> + if (ret == -1) {
> + perror("dup2 returned error");
> + exit(1);
> + }
> +
> + dup2(new_stdout[1], STDOUT_FILENO);
> + if (ret == -1) {
> + perror("dup2 returned error");
> + exit(1);
> + }
> +
> + close(new_stdin[0]);
> + close(new_stdin[1]);
> + close(new_stdout[0]);
> + close(new_stdout[1]);
> +
> + ret = execl("exec_target", "exec_target", (char *) NULL);
> + if (ret == -1) {
> + perror("exec returned error");
> + exit(1);
> + }
> + }
> +
> + close(new_stdin[0]);
> + close(new_stdout[1]);
> +
> + ret = write(new_stdin[1], &val, sizeof(size_t));
> + if (ret == -1) {
> + perror("write returned error");
> + return -1;
> + }
> +
> + /*
> + * wait for the worker to finish, so that read() reads all data
> + * will also context switch with worker so that this function can be used
> + * for context switch tests
> + */
> + waitpid(pid, &status, 0);
> + if (WIFEXITED(status) == 0) {
> + fprintf(stderr, "worker exited unexpectedly\n");
> + return -1;
> + }
> + if (WEXITSTATUS(status) != 0) {
> + fprintf(stderr, "worker exited with error\n");
> + return -1;
> + }
> +
> + ret = read(new_stdout[0], signed_vals, sizeof(struct signatures));
> + if (ret == -1) {
> + perror("read returned error");
> + return -1;
> + }
> +
> + return 0;
> +}
> +
> /* check that a corrupted PAC results in SIGSEGV */
> TEST_SIGNAL(corrupt_pac, SIGSEGV)
> {
> @@ -79,5 +192,40 @@ TEST(pac_instructions_not_nop_generic)
> ASSERT_NE(0, keyg) TH_LOG("keyg instructions did nothing");
> }
>
> +/*
> + * 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)
> +{
> + struct signatures new_keys;
> + struct signatures old_keys;
> + int ret;
> + int different = 0;
> + int nkeys = NKEYS;
> + unsigned long hwcaps = getauxval(AT_HWCAP);
> +
> + /* generic and data key instructions are not in NOP space. This prevents a SIGILL */
> + ASSERT_NE(0, hwcaps & HWCAP_PACA) TH_LOG("PAUTH not enabled");
> + if (!(hwcaps & HWCAP_PACG)) {
> + TH_LOG("WARNING: Generic PAUTH not enabled. Skipping generic key checks");
> + nkeys = NKEYS - 1;
> + }
> +
> + for (int i = 0; i < PAC_COLLISION_ATTEMPTS; i++) {
> + ret = exec_sign_all(&new_keys, i);
> + ASSERT_EQ(0, ret) TH_LOG("failed to run worker");
> +
> + if (nkeys == NKEYS)
> + sign_all(&old_keys, i);
> + else
> + sign_specific(&old_keys, i);
> +
> + different |= !are_same(&old_keys, &new_keys, nkeys);
> + }
> +
> + ASSERT_EQ(1, different) TH_LOG("exec() did not change keys");
> +}
> +
> TEST_HARNESS_MAIN
>
>
--
Regards,
Vincenzo
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