Re: [PATCH 08/10] selftests/x86: Add a sigframe insufficient xstate_size test

[Alexander Mikhalitsyn]

Am Mo., 15. Juni 2026 um 21:40 Uhr schrieb Andrei Vagin <avagin@xxxxxxxxxx>:
>
> Extend sigframe_fpu_portability to include an insufficient xstate_size
> check (test_insufficient_xstate_size). Verify that the kernel correctly
> rejects signal frames where the xstate_size is too small for the enabled
> features in the xfeatures mask.
>
> Signed-off-by: Andrei Vagin <avagin@xxxxxxxxxx>

Reviewed-by: Alexander Mikhalitsyn <aleksandr.mikhalitsyn@xxxxxxxxxxxxxx>

> ---
>  .../selftests/x86/sigframe_fpu_portability.c  | 68 +++++++++++++++++--
>  1 file changed, 62 insertions(+), 6 deletions(-)
>
> diff --git a/tools/testing/selftests/x86/sigframe_fpu_portability.c b/tools/testing/selftests/x86/sigframe_fpu_portability.c
> index 169548892f92..462219905303 100644
> --- a/tools/testing/selftests/x86/sigframe_fpu_portability.c
> +++ b/tools/testing/selftests/x86/sigframe_fpu_portability.c
> @@ -12,19 +12,24 @@
>  #include <sys/syscall.h>
>  #include <asm/prctl.h>
>  #include <stddef.h>
> +#include <setjmp.h>
>
>  #include "helpers.h"
>  #include "xstate.h"
>
>  /*
> - * This test verifies the FPU portability of the signal frame.
> - * It verifies that the kernel correctly restores the xstate context even
> - * if the frame size has been manually reduced (shrunk), as long as the
> - * FP_XSTATE_MAGIC2 marker is correctly placed.
> + * This test verifies the FPU portability and consistency of the signal frame.
> + *
> + * - test_shrunk_xstate_size:
> + *   Verifies that the kernel restores state from a frame with xstate_size
> + *   shrunk to only include active features.
> + *
> + * - test_insufficient_xstate_size:
> + *   Verifies that the kernel rejects a frame if xstate_size is too small for
> + *   the features enabled in xfeatures.
>   */
>
>  #define SIGFRAME_XSTATE_HDR_OFFSET     512
> -
>  #define XSTATE_SSE_ONLY_SIZE   (SIGFRAME_XSTATE_HDR_OFFSET + XSAVE_HDR_SIZE)
>  #define XFEATURE_MASK_FPSSE    ((1 << XFEATURE_FP) | (1 << XFEATURE_SSE))
>
> @@ -148,15 +153,66 @@ static void test_shrunk_xstate_size(void)
>         clearhandler(SIGUSR1);
>  }
>
> +static sigjmp_buf segv_jmpbuf;
> +
> +static void handle_segv(int sig, siginfo_t *si, void *ucp)
> +{
> +       siglongjmp(segv_jmpbuf, 1);
> +}
> +
> +static void handle_insufficient_xstate_size(int sig, siginfo_t *si, void *ucp)
> +{
> +       ucontext_t *uc = ucp;
> +       void *fp = uc->uc_mcontext.fpregs;
> +       struct _fpx_sw_bytes *sw = get_fpx_sw_bytes(fp);
> +
> +       /* The origin frame contains an AVX state. */
> +       sw->xstate_size = XSTATE_SSE_ONLY_SIZE;
> +
> +       *(uint32_t *)(fp + sw->xstate_size) = FP_XSTATE_MAGIC2;
> +}
> +
> +static void test_insufficient_xstate_size(void)
> +{
> +       uint64_t v[4] = {0, 0, 0, 0};
> +
> +       sig_err_buf[0] = 0;
> +       sethandler(SIGUSR1, handle_insufficient_xstate_size, 0);
> +       sethandler(SIGSEGV, handle_segv, 0);
> +
> +       v[0] = 0x1111111111111111ULL;
> +       v[1] = 0x2222222222222222ULL;
> +       v[2] = 0x3333333333333333ULL;
> +       v[3] = 0x4444444444444444ULL;
> +       write_ymm0(v);
> +
> +       if (sigsetjmp(segv_jmpbuf, 1) == 0) {
> +               raise(SIGUSR1);
> +               sig_print("Inconsistent size was NOT rejected\n");
> +       }
> +
> +       clearhandler(SIGUSR1);
> +       clearhandler(SIGSEGV);
> +
> +       if (sig_err_buf[0])
> +               ksft_test_result_fail("%s\n", sig_err_buf);
> +       else
> +               ksft_test_result_pass("Inconsistent size correctly rejected\n");
> +
> +       clearhandler(SIGUSR1);
> +       clearhandler(SIGSEGV);
> +}
>
>  int main(void)
>  {
>         ksft_print_header();
> -       ksft_set_plan(1);
> +       ksft_set_plan(2);
>
>         check_avx_support();
>
>         test_shrunk_xstate_size();
> +       test_insufficient_xstate_size();
> +
>         ksft_finished();
>         return 0;
>  }
> --
> 2.54.0.1189.g8c84645362-goog
>
>