PING: [PATCH 1/3] CET: Rename CET_MAX to CET_CONTROL_MASK [BZ #25887]

["H.J. Lu" <hjl.tools@gmail.com>]

On Tue, Apr 28, 2020 at 2:52 PM H.J. Lu <hjl.tools@gmail.com> wrote:
>
> _dl_x86_feature_1[1] is used to control each CET feature, IBT and SHSTK:
>
>  /* Valid control values:
>     0: Enable CET features based on ELF property note.
>     1: Always disable CET features.
>     2: Always enable CET features.
>     3: Enable CET features permissively.
>   */
>  #define CET_ELF_PROPERTY       0
>  #define CET_ALWAYS_OFF         1
>  #define CET_ALWAYS_ON          2
>  #define CET_PERMISSIVE         3
>  #define CET_MAX                CET_PERMISSIVE
>
> CET control value takes 2 bits.  Rename CET_MAX to CET_CONTROL_MASK.  Add
> CET_IBT_SHIFT and CET_SHSTK_SHIFT.
> ---
>  sysdeps/x86/cet-tunables.h | 22 +++++++++++++++++++--
>  sysdeps/x86/cpu-features.c |  7 +++----
>  sysdeps/x86/cpu-tunables.c | 39 +++++++++++++++-----------------------
>  sysdeps/x86/dl-cet.c       |  6 ++----
>  4 files changed, 40 insertions(+), 34 deletions(-)
>
> diff --git a/sysdeps/x86/cet-tunables.h b/sysdeps/x86/cet-tunables.h
> index 5e1e42df10..0088b89d3e 100644
> --- a/sysdeps/x86/cet-tunables.h
> +++ b/sysdeps/x86/cet-tunables.h
> @@ -16,14 +16,32 @@
>     License along with the GNU C Library; if not, see
>     <https://www.gnu.org/licenses/>.  */
>
> -/* Valid control values:
> +#ifndef _CET_TUNABLES_H
> +#define _CET_TUNABLES_H
> +
> +/* For each CET feature, IBT and SHSTK, valid control values:
>     0: Enable CET features based on ELF property note.
>     1: Always disable CET features.
>     2: Always enable CET features.
>     3: Enable CET features permissively.
> +
> +   Bits 0-1: IBT
> +   Bits 2-3: SHSTK
>   */
>  #define CET_ELF_PROPERTY       0
>  #define CET_ALWAYS_OFF         1
>  #define CET_ALWAYS_ON          2
>  #define CET_PERMISSIVE         3
> -#define CET_MAX                        CET_PERMISSIVE
> +#define CET_CONTROL_MASK       3
> +#define CET_IBT_SHIFT          0
> +#define CET_SHSTK_SHIFT                2
> +
> +/* Get CET control value.  */
> +
> +static inline unsigned int
> +get_cet_control_value (unsigned int shift)
> +{
> +  return (GL(dl_x86_feature_1)[1] >> shift) & CET_CONTROL_MASK;
> +}
> +
> +#endif /* cet-tunables.h */
> diff --git a/sysdeps/x86/cpu-features.c b/sysdeps/x86/cpu-features.c
> index 81a170a819..76a6476607 100644
> --- a/sysdeps/x86/cpu-features.c
> +++ b/sysdeps/x86/cpu-features.c
> @@ -594,10 +594,9 @@ no_cpuid:
>             }
>
>           /* Lock CET if IBT or SHSTK is enabled in executable.  Don't
> -            lock CET if SHSTK is enabled permissively.  */
> -         if (((GL(dl_x86_feature_1)[1] >> CET_MAX)
> -              & ((1 << CET_MAX) - 1))
> -              != CET_PERMISSIVE)
> +            lock CET if IBT or SHSTK is enabled permissively.  */
> +         if (get_cet_control_value (CET_IBT_SHIFT) != CET_PERMISSIVE
> +             && get_cet_control_value (CET_SHSTK_SHIFT) != CET_PERMISSIVE)
>             dl_cet_lock_cet ();
>         }
>  # endif
> diff --git a/sysdeps/x86/cpu-tunables.c b/sysdeps/x86/cpu-tunables.c
> index 861bd7bcaa..c8fc5e67d9 100644
> --- a/sysdeps/x86/cpu-tunables.c
> +++ b/sysdeps/x86/cpu-tunables.c
> @@ -338,26 +338,26 @@ TUNABLE_CALLBACK (set_hwcaps) (tunable_val_t *valp)
>  # if CET_ENABLED
>  #  include <cet-tunables.h>
>
> +/* Set CET control value.  */
> +
> +static inline void
> +set_cet_control_value (unsigned int value, unsigned int shift)
> +{
> +   GL(dl_x86_feature_1)[1] &= ~(CET_CONTROL_MASK << shift);
> +   GL(dl_x86_feature_1)[1] |= value << shift;
> +}
> +
>  attribute_hidden
>  void
>  TUNABLE_CALLBACK (set_x86_ibt) (tunable_val_t *valp)
>  {
>    if (DEFAULT_MEMCMP (valp->strval, "on", sizeof ("on")) == 0)
> -    {
> -      GL(dl_x86_feature_1)[1] &= ~((1 << CET_MAX) - 1);
> -      GL(dl_x86_feature_1)[1] |= CET_ALWAYS_ON;
> -    }
> +    set_cet_control_value (CET_ALWAYS_ON, CET_IBT_SHIFT);
>    else if (DEFAULT_MEMCMP (valp->strval, "off", sizeof ("off")) == 0)
> -    {
> -      GL(dl_x86_feature_1)[1] &= ~((1 << CET_MAX) - 1);
> -      GL(dl_x86_feature_1)[1] |= CET_ALWAYS_OFF;
> -    }
> +    set_cet_control_value (CET_ALWAYS_OFF, CET_IBT_SHIFT);
>    else if (DEFAULT_MEMCMP (valp->strval, "permissive",
>                            sizeof ("permissive")) == 0)
> -    {
> -      GL(dl_x86_feature_1)[1] &= ~((1 << CET_MAX) - 1);
> -      GL(dl_x86_feature_1)[1] |= CET_PERMISSIVE;
> -    }
> +    set_cet_control_value (CET_PERMISSIVE, CET_IBT_SHIFT);
>  }
>
>  attribute_hidden
> @@ -365,21 +365,12 @@ void
>  TUNABLE_CALLBACK (set_x86_shstk) (tunable_val_t *valp)
>  {
>    if (DEFAULT_MEMCMP (valp->strval, "on", sizeof ("on")) == 0)
> -    {
> -      GL(dl_x86_feature_1)[1] &= ~(((1 << CET_MAX) - 1) << CET_MAX);
> -      GL(dl_x86_feature_1)[1] |= (CET_ALWAYS_ON << CET_MAX);
> -    }
> +    set_cet_control_value (CET_ALWAYS_ON, CET_SHSTK_SHIFT);
>    else if (DEFAULT_MEMCMP (valp->strval, "off", sizeof ("off")) == 0)
> -    {
> -      GL(dl_x86_feature_1)[1] &= ~(((1 << CET_MAX) - 1) << CET_MAX);
> -      GL(dl_x86_feature_1)[1] |= (CET_ALWAYS_OFF << CET_MAX);
> -    }
> +    set_cet_control_value (CET_ALWAYS_OFF, CET_SHSTK_SHIFT);
>    else if (DEFAULT_MEMCMP (valp->strval, "permissive",
>                            sizeof ("permissive")) == 0)
> -    {
> -      GL(dl_x86_feature_1)[1] &= ~(((1 << CET_MAX) - 1) << CET_MAX);
> -      GL(dl_x86_feature_1)[1] |= (CET_PERMISSIVE << CET_MAX);
> -    }
> +    set_cet_control_value (CET_PERMISSIVE, CET_SHSTK_SHIFT);
>  }
>  # endif
>  #endif
> diff --git a/sysdeps/x86/dl-cet.c b/sysdeps/x86/dl-cet.c
> index c7029f1b51..0f115540aa 100644
> --- a/sysdeps/x86/dl-cet.c
> +++ b/sysdeps/x86/dl-cet.c
> @@ -39,11 +39,9 @@ static void
>  dl_cet_check (struct link_map *m, const char *program)
>  {
>    /* Check how IBT should be enabled.  */
> -  unsigned int enable_ibt_type
> -    = GL(dl_x86_feature_1)[1] & ((1 << CET_MAX) - 1);
> +  unsigned int enable_ibt_type = get_cet_control_value (CET_IBT_SHIFT);
>    /* Check how SHSTK should be enabled.  */
> -  unsigned int enable_shstk_type
> -    = ((GL(dl_x86_feature_1)[1] >> CET_MAX) & ((1 << CET_MAX) - 1));
> +  unsigned int enable_shstk_type = get_cet_control_value (CET_SHSTK_SHIFT);
>
>    /* No legacy object check if both IBT and SHSTK are always on.  */
>    if (enable_ibt_type == CET_ALWAYS_ON
> --
> 2.25.4
>

PING.

-- 
H.J.