[Bug dynamic-link/25887] New: Wasted space in _dl_x86_feature_1[1]

[Bug dynamic-link/25887] New: Wasted space in _dl_x86_feature_1[1]

[hjl.tools at gmail dot com]

https://sourceware.org/bugzilla/show_bug.cgi?id=25887

            Bug ID: 25887
           Summary: Wasted space in _dl_x86_feature_1[1]
           Product: glibc
           Version: 2.32
            Status: NEW
          Severity: normal
          Priority: P2
         Component: dynamic-link
          Assignee: unassigned at sourceware dot org
          Reporter: hjl.tools at gmail dot com
  Target Milestone: ---
            Target: i386,x86-64

_dl_x86_feature_1[1] is used to control CET:

/* 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

For each CET feature, IBT and SHSTK, it takes 2 bits.  There are

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;
    }   
  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;
    }
  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;
    }
}

attribute_hidden
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);
    }
  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);
    }
  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);
    }
}

CET_MAX should be renamed to CET_CONTROL_BITS and set to 2.

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[Bug dynamic-link/25887] Wasted space in _dl_x86_feature_1[1]

[hjl.tools at gmail dot com]

https://sourceware.org/bugzilla/show_bug.cgi?id=25887

H.J. Lu <hjl.tools at gmail dot com> changed:

           What    |Removed                     |Added
----------------------------------------------------------------------------
                 CC|                            |fweimer at redhat dot com

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[Bug dynamic-link/25887] Wasted space in _dl_x86_feature_1[1]

[hjl.tools at gmail dot com]

https://sourceware.org/bugzilla/show_bug.cgi?id=25887

H.J. Lu <hjl.tools at gmail dot com> changed:

           What    |Removed                     |Added
----------------------------------------------------------------------------
   Target Milestone|---                         |2.32
             Status|NEW                         |RESOLVED
         Resolution|---                         |FIXED

--- Comment #1 from H.J. Lu <hjl.tools at gmail dot com> ---
Fixed by

commit 674ea88294bfb8d89878a0ebbbcec38a85e118a5
Author: H.J. Lu <hjl.tools@gmail.com>
Date:   Tue Apr 28 10:05:25 2020 -0700

    x86: Move CET control to _dl_x86_feature_control [BZ #25887]

    1. Include <dl-procruntime.c> to get architecture specific initializer in
    rtld_global.
    2. Change _dl_x86_feature_1[2] to _dl_x86_feature_1.
    3. Add _dl_x86_feature_control after _dl_x86_feature_1, which is a
    struct of 2 bitfields for IBT and SHSTK control

    This fixes [BZ #25887].

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