Re: [PATCH] x86-64/cet: Make CET feature check specific to Linux/x86

[Noah Goldstein <goldstein.w.n@gmail.com>]

On Wed, Jan 10, 2024 at 8:49 AM H.J. Lu <hjl.tools@gmail.com> wrote:
>
> CET feature bits in TCB, which are Linux specific, are used to check if
> CET features are active.  Move CET feature check to Linux/x86 directory.
> ---
>  .../sysv/linux/x86/bits/platform/features.h   | 48 +++++++++++++++++++
>  sysdeps/unix/sysv/linux/x86_64/dl-cet.h       |  8 ++++
>  .../linux/x86_64/get-cpuid-feature-leaf.c     | 24 ++++++++++
>  sysdeps/x86/Makefile                          |  6 ++-
>  sysdeps/x86/bits/platform/features.h          | 27 +++++++++++
>  sysdeps/x86/bits/platform/x86.h               |  8 ----
>  sysdeps/x86/get-cpuid-feature-leaf.c          |  8 ----
>  sysdeps/x86/sys/platform/x86.h                | 19 ++------
>  sysdeps/x86_64/dl-machine.h                   |  9 ++--
>  9 files changed, 120 insertions(+), 37 deletions(-)
>  create mode 100644 sysdeps/unix/sysv/linux/x86/bits/platform/features.h
>  create mode 100644 sysdeps/unix/sysv/linux/x86_64/get-cpuid-feature-leaf.c
>  create mode 100644 sysdeps/x86/bits/platform/features.h
>
> diff --git a/sysdeps/unix/sysv/linux/x86/bits/platform/features.h b/sysdeps/unix/sysv/linux/x86/bits/platform/features.h
> new file mode 100644
> index 0000000000..7704febe92
> --- /dev/null
> +++ b/sysdeps/unix/sysv/linux/x86/bits/platform/features.h
> @@ -0,0 +1,48 @@
> +/* Inline functions for x86 CPU features.
> +   This file is part of the GNU C Library.
> +   Copyright (C) 2024 Free Software Foundation, Inc.
> +
> +   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/>.  */
> +
> +#ifndef _SYS_PLATFORM_X86_H
> +# error "Never include <bits/platform/features.h> directly; use <sys/platform/x86.h> instead."
> +#endif
> +
> +/* Bits in the feature_1 field in TCB.  */
> +
> +enum
> +{
> +  x86_feature_1_ibt            = 1U << 0,
> +  x86_feature_1_shstk          = 1U << 1
> +};
> +
> +static __inline__ _Bool
> +x86_cpu_cet_active (unsigned int __index)
> +{
> +#ifdef __x86_64__
> +  unsigned int __feature_1;
> +# ifdef __LP64__
> +  __asm__ ("mov %%fs:72, %0" : "=r" (__feature_1));
> +# else
> +  __asm__ ("mov %%fs:40, %0" : "=r" (__feature_1));
> +# endif
> +  if (__index == x86_cpu_IBT)
> +    return __feature_1 & x86_feature_1_ibt;
> +  else
> +    return __feature_1 & x86_feature_1_shstk;
> +#else
> +  return false;
> +#endif
> +}
> diff --git a/sysdeps/unix/sysv/linux/x86_64/dl-cet.h b/sysdeps/unix/sysv/linux/x86_64/dl-cet.h
> index a00c7ee662..1fe3133406 100644
> --- a/sysdeps/unix/sysv/linux/x86_64/dl-cet.h
> +++ b/sysdeps/unix/sysv/linux/x86_64/dl-cet.h
> @@ -54,6 +54,14 @@ dl_cet_get_cet_status (void)
>    return status;
>  }
>
> +static __always_inline bool
> +dl_cet_ibt_enabled (void)
> +{
> +  unsigned int feature_1 = THREAD_GETMEM (THREAD_SELF,
> +                                         header.feature_1);
> +  return (feature_1 & GNU_PROPERTY_X86_FEATURE_1_IBT) != 0;
> +}
> +
>  /* Enable shadow stack with a macro to avoid shadow stack underflow.  */
>  #define ENABLE_X86_CET(cet_feature)                            \
>    if ((cet_feature & GNU_PROPERTY_X86_FEATURE_1_SHSTK))                \
> diff --git a/sysdeps/unix/sysv/linux/x86_64/get-cpuid-feature-leaf.c b/sysdeps/unix/sysv/linux/x86_64/get-cpuid-feature-leaf.c
> new file mode 100644
> index 0000000000..39b342463c
> --- /dev/null
> +++ b/sysdeps/unix/sysv/linux/x86_64/get-cpuid-feature-leaf.c
> @@ -0,0 +1,24 @@
> +/* Get CPUID feature leaf.  Linux/x86-64 version.
> +   Copyright (C) 2024 Free Software Foundation, Inc.
> +
> +   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 <sysdeps/x86/get-cpuid-feature-leaf.c>
> +
> +#ifdef __LP64__
> +_Static_assert (FEATURE_1_OFFSET == 72, "FEATURE_1_OFFSET != 72");
> +#else
> +_Static_assert (FEATURE_1_OFFSET == 40, "FEATURE_1_OFFSET != 40");
> +#endif
> diff --git a/sysdeps/x86/Makefile b/sysdeps/x86/Makefile
> index bf913594c1..4d50b327b5 100644
> --- a/sysdeps/x86/Makefile
> +++ b/sysdeps/x86/Makefile
> @@ -5,7 +5,11 @@ endif
>  ifeq ($(subdir),elf)
>  sysdep_routines += get-cpuid-feature-leaf
>  sysdep-dl-routines += dl-get-cpu-features
> -sysdep_headers += sys/platform/x86.h bits/platform/x86.h
> +sysdep_headers += \
> +  bits/platform/features.h \
> +  bits/platform/x86.h \
> +  sys/platform/x86.h \
> +# sysdep_headers
>
>  CFLAGS-dl-get-cpu-features.os += $(rtld-early-cflags)
>  CFLAGS-get-cpuid-feature-leaf.o += $(no-stack-protector)
> diff --git a/sysdeps/x86/bits/platform/features.h b/sysdeps/x86/bits/platform/features.h
> new file mode 100644
> index 0000000000..f02489266e
> --- /dev/null
> +++ b/sysdeps/x86/bits/platform/features.h
> @@ -0,0 +1,27 @@
> +/* Inline functions for x86 CPU features.
> +   This file is part of the GNU C Library.
> +   Copyright (C) 2024 Free Software Foundation, Inc.
> +
> +   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/>.  */
> +
> +#ifndef _SYS_PLATFORM_X86_H
> +# error "Never include <bits/platform/features.h> directly; use <sys/platform/x86.h> instead."
> +#endif
> +
> +static __inline__ _Bool
> +x86_cpu_cet_active (unsigned int __index)
> +{
> +  return false;
> +}
> diff --git a/sysdeps/x86/bits/platform/x86.h b/sysdeps/x86/bits/platform/x86.h
> index c31d086194..8b157d99b3 100644
> --- a/sysdeps/x86/bits/platform/x86.h
> +++ b/sysdeps/x86/bits/platform/x86.h
> @@ -337,11 +337,3 @@ enum
>    x86_cpu_AVX10_YMM = x86_cpu_index_24_ecx_0_ebx + 17,
>    x86_cpu_AVX10_ZMM = x86_cpu_index_24_ecx_0_ebx + 18,
>  };
> -
> -/* Bits in the feature_1 field in TCB.  */
> -
> -enum
> -{
> -  x86_feature_1_ibt            = 1U << 0,
> -  x86_feature_1_shstk          = 1U << 1
> -};
> diff --git a/sysdeps/x86/get-cpuid-feature-leaf.c b/sysdeps/x86/get-cpuid-feature-leaf.c
> index e6a41cc79c..6f67346081 100644
> --- a/sysdeps/x86/get-cpuid-feature-leaf.c
> +++ b/sysdeps/x86/get-cpuid-feature-leaf.c
> @@ -19,14 +19,6 @@
>  #include <tcb-offsets.h>
>  #include <ldsodefs.h>
>
> -#ifdef __x86_64__
> -# ifdef __LP64__
> -_Static_assert (FEATURE_1_OFFSET == 72, "FEATURE_1_OFFSET != 72");
> -# else
> -_Static_assert (FEATURE_1_OFFSET == 40, "FEATURE_1_OFFSET != 40");
> -# endif
> -#endif
> -
>  const struct cpuid_feature *
>  __x86_get_cpuid_feature_leaf (unsigned int leaf)
>  {
> diff --git a/sysdeps/x86/sys/platform/x86.h b/sysdeps/x86/sys/platform/x86.h
> index 4d77c0991d..b8066ccc9f 100644
> --- a/sysdeps/x86/sys/platform/x86.h
> +++ b/sysdeps/x86/sys/platform/x86.h
> @@ -22,6 +22,7 @@
>  #include <features.h>
>  #include <stdbool.h>
>  #include <bits/platform/x86.h>
> +#include <bits/platform/features.h>
>
>  __BEGIN_DECLS
>
> @@ -46,22 +47,8 @@ static __inline__ _Bool
>  x86_cpu_active (unsigned int __index)
>  {
>    if (__index == x86_cpu_IBT || __index == x86_cpu_SHSTK)
> -    {
> -#ifdef __x86_64__
> -      unsigned int __feature_1;
> -# ifdef __LP64__
> -      __asm__ ("mov %%fs:72, %0" : "=r" (__feature_1));
> -# else
> -      __asm__ ("mov %%fs:40, %0" : "=r" (__feature_1));
> -# endif
> -      if (__index == x86_cpu_IBT)
> -       return __feature_1 & x86_feature_1_ibt;
> -      else
> -       return __feature_1 & x86_feature_1_shstk;
> -#else
> -      return false;
> -#endif
> -    }
> +    return x86_cpu_cet_active (__index);
> +
>    const struct cpuid_feature *__ptr = __x86_get_cpuid_feature_leaf
>      (__index / (8 * sizeof (unsigned int) * 4));
>    unsigned int __reg
> diff --git a/sysdeps/x86_64/dl-machine.h b/sysdeps/x86_64/dl-machine.h
> index 2d2ce503a5..6d605d0d32 100644
> --- a/sysdeps/x86_64/dl-machine.h
> +++ b/sysdeps/x86_64/dl-machine.h
> @@ -587,10 +587,11 @@ x86_64_rewrite_plt (struct link_map *map, ElfW(Addr) plt_rewrite)
>    const ElfW(Rela) *reloc = (const void *) start;
>    const ElfW(Rela) *reloc_end = (const void *) (start + size);
>
> -  unsigned int feature_1 = THREAD_GETMEM (THREAD_SELF,
> -                                         header.feature_1);
> -  bool ibt_enabled_p
> -    = (feature_1 & GNU_PROPERTY_X86_FEATURE_1_IBT) != 0;
> +# ifdef __CET__
> +  bool ibt_enabled_p = dl_cet_ibt_enabled ();
> +# else
> +  bool ibt_enabled_p = false;
> +# endif
>
>    if (__glibc_unlikely (GLRO(dl_debug_mask) & DL_DEBUG_FILES))
>      _dl_debug_printf ("\nchanging PLT in '%s' to direct branch\n",
> --
> 2.43.0
>

LGTM.
Reviewed-by: Noah Goldstein <goldstein.w.n@gmail.com>