[PATCH] x86: Use HAS_CPU_FEATURE with IBT and SHSTK [BZ #26625]

[H.J. Lu]

On Wed, Sep 16, 2020 at 5:55 AM H.J. Lu <hjl.tools@gmail.com> wrote:
>
> commit 04bba1e5d84b6fd8d3a3b006bc240cd5d241ee30
> Author: H.J. Lu <hjl.tools@gmail.com>
> Date:   Wed Aug 5 13:51:56 2020 -0700
>
>     x86: Set CPU usable feature bits conservatively [BZ #26552]
>
>     Set CPU usable feature bits only for CPU features which are usable in
>     user space and whose usability can be detected from user space, excluding
>     features like FSGSBASE whose enable bit can only be checked in the kernel.
>
> no longer turns on the usable bits of IBT and SHSTK since we don't know
> if IBT and SHSTK are usable much later.  Use HAS_CPU_FEATURE to check if
> the processor supports IBT and SHSTK.
> ---
>  sysdeps/x86/cpu-features.c         | 4 ++--
>  sysdeps/x86/dl-cet.c               | 4 ++--
>  sysdeps/x86/tst-get-cpu-features.c | 2 --
>  3 files changed, 4 insertions(+), 6 deletions(-)
>
> diff --git a/sysdeps/x86/cpu-features.c b/sysdeps/x86/cpu-features.c
> index a9945b94bb..6551df19c0 100644
> --- a/sysdeps/x86/cpu-features.c
> +++ b/sysdeps/x86/cpu-features.c
> @@ -723,9 +723,9 @@ no_cpuid:
>              GLIBC_TUNABLES=glibc.cpu.hwcaps=-IBT,-SHSTK
>            */
>           unsigned int cet_feature = 0;
> -         if (!CPU_FEATURE_USABLE (IBT))
> +         if (!HAS_CPU_FEATURE (IBT))
>             cet_feature |= GNU_PROPERTY_X86_FEATURE_1_IBT;
> -         if (!CPU_FEATURE_USABLE (SHSTK))
> +         if (!HAS_CPU_FEATURE (SHSTK))
>             cet_feature |= GNU_PROPERTY_X86_FEATURE_1_SHSTK;
>
>           if (cet_feature)
> diff --git a/sysdeps/x86/dl-cet.c b/sysdeps/x86/dl-cet.c
> index 03572f7af6..5524b66038 100644
> --- a/sysdeps/x86/dl-cet.c
> +++ b/sysdeps/x86/dl-cet.c
> @@ -74,10 +74,10 @@ dl_cet_check (struct link_map *m, const char *program)
>
>              GLIBC_TUNABLES=glibc.cpu.hwcaps=-IBT,-SHSTK
>            */
> -         enable_ibt &= (CPU_FEATURE_USABLE (IBT)
> +         enable_ibt &= (HAS_CPU_FEATURE (IBT)
>                          && (enable_ibt_type == cet_always_on
>                              || (m->l_cet & lc_ibt) != 0));
> -         enable_shstk &= (CPU_FEATURE_USABLE (SHSTK)
> +         enable_shstk &= (HAS_CPU_FEATURE (SHSTK)
>                            && (enable_shstk_type == cet_always_on
>                                || (m->l_cet & lc_shstk) != 0));
>         }
> diff --git a/sysdeps/x86/tst-get-cpu-features.c b/sysdeps/x86/tst-get-cpu-features.c
> index a3225a00e6..d11eac9853 100644
> --- a/sysdeps/x86/tst-get-cpu-features.c
> +++ b/sysdeps/x86/tst-get-cpu-features.c
> @@ -320,7 +320,6 @@ do_test (void)
>    CHECK_CPU_FEATURE_USABLE (OSPKE);
>    CHECK_CPU_FEATURE_USABLE (WAITPKG);
>    CHECK_CPU_FEATURE_USABLE (AVX512_VBMI2);
> -  CHECK_CPU_FEATURE_USABLE (SHSTK);
>    CHECK_CPU_FEATURE_USABLE (GFNI);
>    CHECK_CPU_FEATURE_USABLE (VAES);
>    CHECK_CPU_FEATURE_USABLE (VPCLMULQDQ);
> @@ -344,7 +343,6 @@ do_test (void)
>    CHECK_CPU_FEATURE_USABLE (HYBRID);
>    CHECK_CPU_FEATURE_USABLE (TSXLDTRK);
>    CHECK_CPU_FEATURE_USABLE (PCONFIG);
> -  CHECK_CPU_FEATURE_USABLE (IBT);
>    CHECK_CPU_FEATURE_USABLE (AMX_BF16);
>    CHECK_CPU_FEATURE_USABLE (AMX_TILE);
>    CHECK_CPU_FEATURE_USABLE (AMX_INT8);
> --
> 2.26.2
>

I am checking it in.

-- 
H.J.