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Message-ID: <CAJqdLrow_EEda3Gw8Q9E2VF9pWxa7COUu88fZZiP1-=Mk00DqA@mail.gmail.com>
Date: Tue, 10 Feb 2026 21:37:34 +0100
From: Alexander Mikhalitsyn <alexander@...alicyn.com>
To: Andrei Vagin <avagin@...gle.com>
Cc: Kees Cook <kees@...nel.org>, Andrew Morton <akpm@...ux-foundation.org>,
Cyrill Gorcunov <gorcunov@...il.com>, Mike Rapoport <rppt@...nel.org>, linux-kernel@...r.kernel.org,
linux-fsdevel@...r.kernel.org, linux-mm@...ck.org, criu@...ts.linux.dev,
Chen Ridong <chenridong@...wei.com>, Christian Brauner <brauner@...nel.org>,
David Hildenbrand <david@...nel.org>, Eric Biederman <ebiederm@...ssion.com>,
Lorenzo Stoakes <lorenzo.stoakes@...cle.com>, Michal Koutny <mkoutny@...e.com>
Subject: Re: [PATCH 4/4] selftests/exec: add test for HWCAP inheritance
Am Mo., 9. Feb. 2026 um 20:06 Uhr schrieb Andrei Vagin <avagin@...gle.com>:
>
> Verify that HWCAPs are correctly inherited/preserved across execve() when
> modified via prctl(PR_SET_MM_AUXV).
>
> The test performs the following steps:
> * reads the current AUXV using prctl(PR_GET_AUXV);
> * finds an HWCAP entry and toggles its most significant bit;
> * replaces the AUXV of the current process with the modified one using
> prctl(PR_SET_MM, PR_SET_MM_AUXV);
> * executes itself to verify that the new program sees the modified HWCAP
> value.
>
> Signed-off-by: Andrei Vagin <avagin@...gle.com>
Reviewed-by: Alexander Mikhalitsyn <aleksandr.mikhalitsyn@...urfusion.io>
> ---
> tools/testing/selftests/exec/.gitignore | 1 +
> tools/testing/selftests/exec/Makefile | 1 +
> tools/testing/selftests/exec/hwcap_inherit.c | 105 +++++++++++++++++++
> 3 files changed, 107 insertions(+)
> create mode 100644 tools/testing/selftests/exec/hwcap_inherit.c
>
> diff --git a/tools/testing/selftests/exec/.gitignore b/tools/testing/selftests/exec/.gitignore
> index 7f3d1ae762ec..2ff245fd0ba6 100644
> --- a/tools/testing/selftests/exec/.gitignore
> +++ b/tools/testing/selftests/exec/.gitignore
> @@ -19,3 +19,4 @@ null-argv
> xxxxxxxx*
> pipe
> S_I*.test
> +hwcap_inherit
> \ No newline at end of file
> diff --git a/tools/testing/selftests/exec/Makefile b/tools/testing/selftests/exec/Makefile
> index 45a3cfc435cf..e73005965e05 100644
> --- a/tools/testing/selftests/exec/Makefile
> +++ b/tools/testing/selftests/exec/Makefile
> @@ -20,6 +20,7 @@ TEST_FILES := Makefile
> TEST_GEN_PROGS += recursion-depth
> TEST_GEN_PROGS += null-argv
> TEST_GEN_PROGS += check-exec
> +TEST_GEN_PROGS += hwcap_inherit
>
> EXTRA_CLEAN := $(OUTPUT)/subdir.moved $(OUTPUT)/execveat.moved $(OUTPUT)/xxxxx* \
> $(OUTPUT)/S_I*.test
> diff --git a/tools/testing/selftests/exec/hwcap_inherit.c b/tools/testing/selftests/exec/hwcap_inherit.c
> new file mode 100644
> index 000000000000..1b43b2dbb1d0
> --- /dev/null
> +++ b/tools/testing/selftests/exec/hwcap_inherit.c
> @@ -0,0 +1,105 @@
> +// SPDX-License-Identifier: GPL-2.0
> +
> +#define _GNU_SOURCE
> +#include <sys/auxv.h>
> +#include <sys/prctl.h>
> +#include <sys/wait.h>
> +#include <linux/prctl.h>
> +#include <unistd.h>
> +#include <stdlib.h>
> +#include <stdio.h>
> +#include <string.h>
> +#include <errno.h>
> +#include <elf.h>
> +#include <linux/auxvec.h>
> +
> +#include "../kselftest.h"
> +
> +static int find_msb(unsigned long v)
> +{
> + return sizeof(v)*8 - __builtin_clzl(v) - 1;
> +}
> +
> +int main(int argc, char *argv[])
> +{
> + unsigned long auxv[1024], hwcap, new_hwcap, hwcap_idx;
> + int size, hwcap_type = 0, hwcap_feature, count, status;
> + char hwcap_str[32], hwcap_type_str[32];
> + pid_t pid;
> +
> + if (argc > 1 && strcmp(argv[1], "verify") == 0) {
> + unsigned long type = strtoul(argv[2], NULL, 16);
> + unsigned long expected = strtoul(argv[3], NULL, 16);
> + unsigned long hwcap = getauxval(type);
> +
> + if (hwcap != expected) {
> + ksft_print_msg("HWCAP mismatch: type %lx, expected %lx, got %lx\n",
> + type, expected, hwcap);
> + return 1;
> + }
> + ksft_print_msg("HWCAP matched: %lx\n", hwcap);
> + return 0;
> + }
> +
> + ksft_print_header();
> + ksft_set_plan(1);
> +
> + size = prctl(PR_GET_AUXV, auxv, sizeof(auxv), 0, 0);
> + if (size == -1)
> + ksft_exit_fail_perror("prctl(PR_GET_AUXV)");
> +
> + count = size / sizeof(unsigned long);
> +
> + /* Find the "latest" feature and try to mask it out. */
> + for (int i = 0; i < count - 1; i += 2) {
> + hwcap = auxv[i + 1];
> + if (hwcap == 0)
> + continue;
> + switch (auxv[i]) {
> + case AT_HWCAP4:
> + case AT_HWCAP3:
> + case AT_HWCAP2:
> + case AT_HWCAP:
> + hwcap_type = auxv[i];
> + hwcap_feature = find_msb(hwcap);
> + hwcap_idx = i + 1;
> + break;
> + default:
> + continue;
> + }
> + }
> + if (hwcap_type == 0)
> + ksft_exit_skip("No features found, skipping test\n");
> + hwcap = auxv[hwcap_idx];
> + new_hwcap = hwcap ^ (1UL << hwcap_feature);
> + auxv[hwcap_idx] = new_hwcap;
> +
> + if (prctl(PR_SET_MM, PR_SET_MM_AUXV, auxv, size, 0) < 0) {
> + if (errno == EPERM)
> + ksft_exit_skip("prctl(PR_SET_MM_AUXV) requires CAP_SYS_RESOURCE\n");
> + ksft_exit_fail_perror("prctl(PR_SET_MM_AUXV)");
> + }
> +
> + pid = fork();
> + if (pid < 0)
> + ksft_exit_fail_perror("fork");
> + if (pid == 0) {
> + char *new_argv[] = { argv[0], "verify", hwcap_type_str, hwcap_str, NULL };
> +
> + snprintf(hwcap_str, sizeof(hwcap_str), "%lx", new_hwcap);
> + snprintf(hwcap_type_str, sizeof(hwcap_type_str), "%x", hwcap_type);
> +
> + execv(argv[0], new_argv);
> + perror("execv");
> + exit(1);
> + }
> +
> + if (waitpid(pid, &status, 0) == -1)
> + ksft_exit_fail_perror("waitpid");
> + if (status != 0)
> + ksft_exit_fail_msg("HWCAP inheritance failed (status %d)\n", status);
> +
> + ksft_test_result_pass("HWCAP inheritance succeeded\n");
> + ksft_exit_pass();
> + return 0;
> +}
> --
> 2.53.0.239.g8d8fc8a987-goog
>
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