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From: "hjl.tools at gmail dot com" <sourceware-bugzilla@sourceware.org>
To: glibc-bugs@sourceware.org
Subject: [Bug dynamic-link/31185] New: Incorrect thread point access in
 _dl_tlsdesc_undefweak and _dl_tlsdesc_dynamic
Date: Thu, 21 Dec 2023 03:29:31 +0000
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X-Bugzilla-Product: glibc
X-Bugzilla-Component: dynamic-link
X-Bugzilla-Version: 2.38
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X-Bugzilla-Who: hjl.tools at gmail dot com
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https://sourceware.org/bugzilla/show_bug.cgi?id=3D31185

            Bug ID: 31185
           Summary: Incorrect thread point access in _dl_tlsdesc_undefweak
                    and _dl_tlsdesc_dynamic
           Product: glibc
           Version: 2.38
            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: x32

_dl_tlsdesc_undefweak and _dl_tlsdesc_dynamic in sysdeps/x86_64/dl-tlsdesc.S
access the thread pointer via the tcb field in TCB:

_dl_tlsdesc_undefweak:
        _CET_ENDBR
        movq    8(%rax), %rax
        subq    %fs:0, %rax
        ret=20

_dl_tlsdesc_dynamic:
        ,,,
        subq    %fs:0, %rax
        movq    -8(%rsp), %rdi
        ret

Since the tcb field in TCB is a pointer, %fs:0 is a 32-bit location,
not 64-bit. It should use "sub %fs:0, %RAX_LP" instead.  Since
_dl_tlsdesc_undefweak returns ptrdiff_t and _dl_make_tlsdesc_dynamic
returns void *, RAX_LP is appropriate here for x32.

--=20
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