[PATCH v4 5/5] aarch64: Add GCS test with signal handler

[Adhemerval Zanella Netto]

LGTM, thanks.  Two small issues below.

Reviewed-by: Adhemerval Zanella  <adhemerval.zanella@linaro.org>

On 10/02/25 08:45, Yury Khrustalev wrote:
> Test that when we return from a function that enabled GCS at runtime
> we get SIGSEGV. Also test that ucontext contains GCS block with the
> GCS pointer.
> ---
>  sysdeps/unix/sysv/linux/aarch64/Makefile      |   5 +
>  .../sysv/linux/aarch64/tst-gcs-noreturn.c     | 100 ++++++++++++++++++
>  2 files changed, 105 insertions(+)
>  create mode 100644 sysdeps/unix/sysv/linux/aarch64/tst-gcs-noreturn.c
> 
> diff --git a/sysdeps/unix/sysv/linux/aarch64/Makefile b/sysdeps/unix/sysv/linux/aarch64/Makefile
> index ce24f386a0..0839f0b08c 100644
> --- a/sysdeps/unix/sysv/linux/aarch64/Makefile
> +++ b/sysdeps/unix/sysv/linux/aarch64/Makefile
> @@ -15,6 +15,7 @@ gcs-tests-dynamic = \
>    tst-gcs-dlopen-override \
>    tst-gcs-enforced \
>    tst-gcs-enforced-abort \
> +  tst-gcs-noreturn \
>    tst-gcs-optional-off \
>    tst-gcs-optional-on \
>    tst-gcs-override \
> @@ -123,6 +124,10 @@ $(objpfx)tst-gcs-dlopen-optional-on.out: $(objpfx)tst-gcs-mod2.so
>  $(objpfx)tst-gcs-dlopen-optional-off.out: $(objpfx)tst-gcs-mod2.so
>  $(objpfx)tst-gcs-dlopen-override.out: $(objpfx)tst-gcs-mod2.so
>  
> +LDFLAGS-tst-gcs-noreturn = -Wl,-z gcs=always
> +
> +tst-gcs-noreturn-ENV = GLIBC_TUNABLES=glibc.cpu.aarch64_gcs=0
> +
>  endif # ifeq ($(have-test-cc-gcs),yes)
>  
>  endif # ifeq ($(subdir),misc)
> diff --git a/sysdeps/unix/sysv/linux/aarch64/tst-gcs-noreturn.c b/sysdeps/unix/sysv/linux/aarch64/tst-gcs-noreturn.c
> new file mode 100644
> index 0000000000..80b2d0b8c3
> --- /dev/null
> +++ b/sysdeps/unix/sysv/linux/aarch64/tst-gcs-noreturn.c
> @@ -0,0 +1,100 @@
> +/* AArch64 test for GCS abort when returning to non-GCS address.
> +   Copyright (C) 2025 Free Software Foundation, Inc.
> +   This file is part of the GNU C Library.
> +
> +   The GNU C Library is free software; you can redistribute it and/or
> +   modify it under the terms of the GNU Lesser General Public
> +   License as published by the Free Software Foundation; either
> +   version 2.1 of the License, or (at your option) any later version.
> +
> +   The GNU C Library is distributed in the hope that it will be useful,
> +   but WITHOUT ANY WARRANTY; without even the implied warranty of
> +   MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the GNU
> +   Lesser General Public License for more details.
> +
> +   You should have received a copy of the GNU Lesser General Public
> +   License along with the GNU C Library; if not, see
> +   <https://www.gnu.org/licenses/>.  */
> +
> +#include "tst-gcs-helper.h"
> +
> +#include <sys/prctl.h>
> +#include <signal.h>
> +#include <stdlib.h>
> +
> +# ifndef PR_SET_SHADOW_STACK_STATUS
> +#  define PR_SET_SHADOW_STACK_STATUS	75
> +#  define PR_SHADOW_STACK_ENABLE	(1UL << 0)
> +# endif
> +
> +static void
> +run_with_gcs (void)
> +{
> +  int r = prctl(PR_SET_SHADOW_STACK_STATUS, PR_SHADOW_STACK_ENABLE, 0, 0, 0);

Missing space after function call.

> +  /* Syscall should succeed.  */
> +  TEST_VERIFY (r == 0);
> +  bool gcs_enabled = __check_gcs_status ();
> +  /* Now GCS should be enabled.  */
> +  TEST_VERIFY (gcs_enabled);
> +  printf ("GCS is %s\n", gcs_enabled ? "enabled" : "disabled");
> +}
> +
> +static struct _aarch64_ctx *
> +extension (void *p)
> +{
> +  return p;
> +}
> +
> +#ifndef GCS_MAGIC
> +#define GCS_MAGIC 0x47435300
> +#endif
> +
> +static void
> +handler (int sig, siginfo_t *si, void *ctx)
> +{
> +  TEST_VERIFY (sig == SIGSEGV);
> +  ucontext_t *uc = ctx;
> +  void *p = uc->uc_mcontext.__reserved;
> +  if (extension (p)->magic == FPSIMD_MAGIC)
> +    p = (char *)p + extension (p)->size;
> +  if (extension (p)->magic == GCS_MAGIC)
> +    {
> +      struct { uint64_t x, gcspr, y, z; } *q = p;
> +      printf ("GCS pointer: %016lx\n", q->gcspr);
> +      exit (0);
> +    }
> +  else
> +    exit (3);
> +}
> +
> +static int
> +do_test (void)
> +{
> +  /* Check if GCS could possible by enabled.  */
> +  if (!(getauxval (AT_HWCAP) & HWCAP_GCS))
> +    {
> +      puts ("kernel or CPU does not support GCS");
> +      return EXIT_UNSUPPORTED;
> +    }
> +  bool gcs_enabled = __check_gcs_status ();
> +  /* This test should be rung with GCS initially disabled.  */
> +  TEST_VERIFY (!gcs_enabled);
> +
> +  /* We can't use EXPECTED_SIGNAL because of cases when
> +     this test runs on a system that does not support GCS
> +     which is being detected at runtime.  */
> +  struct sigaction sigact;
> +  sigemptyset (&sigact.sa_mask);
> +  sigact.sa_flags = 0;
> +  sigact.sa_flags = sigact.sa_flags | SA_SIGINFO;
> +  sigact.sa_sigaction = handler;
> +  sigaction (SIGSEGV, &sigact, NULL);

Use xsigaction here.

> +
> +  run_with_gcs ();
> +  /* If we reached this point, then something went wrong.
> +     Returning from a function that enabled GCS should result in
> +     SIGSEGV that we catch with the handler set up above.  */
> +  return 2;
> +}
> +
> +#include <support/test-driver.c>