[Bug dynamic-link/30452] New: elf/tst-map-32bit-1a fails with binutils-2.30-117.el8.x86_64

[Bug dynamic-link/30452] New: elf/tst-map-32bit-1a fails with binutils-2.30-117.el8.x86_64

[fweimer at redhat dot com]

https://sourceware.org/bugzilla/show_bug.cgi?id=30452

            Bug ID: 30452
           Summary: elf/tst-map-32bit-1a fails with
                    binutils-2.30-117.el8.x86_64
           Product: glibc
           Version: 2.38
            Status: NEW
          Severity: normal
          Priority: P2
         Component: dynamic-link
          Assignee: unassigned at sourceware dot org
          Reporter: fweimer at redhat dot com
  Target Milestone: ---
            Target: x86_64-linux-gnu

For some reason, BFD ld produces load segments which are 2 MiB aligned:

  LOAD           0x000000 0x0000000000000000 0x0000000000000000 0x000ff0
0x000ff0 R E 0x200000
  LOAD           0x001e00 0x0000000000201e00 0x0000000000201e00 0x000270
0x000280 RW  0x200000

This means that the fast path in _dl_map_segment is not taken, and the
combination of address zero with MAP_DENYWRITE is never used, so MAP_32BIT
handling does not kick in.

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[Bug dynamic-link/30452] LD_PREFER_MAP_32BIT_EXEC does not work with 2MiB load segment alignment

[fweimer at redhat dot com]

https://sourceware.org/bugzilla/show_bug.cgi?id=30452

Florian Weimer <fweimer at redhat dot com> changed:

           What    |Removed                     |Added
----------------------------------------------------------------------------
            Summary|elf/tst-map-32bit-1a fails  |LD_PREFER_MAP_32BIT_EXEC
                   |with                        |does not work with 2MiB
                   |binutils-2.30-117.el8.x86_6 |load segment alignment
                   |4                           |
                 CC|                            |fweimer at redhat dot com

--- Comment #1 from Florian Weimer <fweimer at redhat dot com> ---
Seen with binutils-2.30-117.el8.x86_64.

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[Bug dynamic-link/30452] LD_PREFER_MAP_32BIT_EXEC does not work with 2MiB load segment alignment

[hjl.tools at gmail dot com]

https://sourceware.org/bugzilla/show_bug.cgi?id=30452

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

           What    |Removed                     |Added
----------------------------------------------------------------------------
                 CC|                            |hjl.tools at gmail dot com

--- Comment #2 from H.J. Lu <hjl.tools at gmail dot com> ---
This won't work with 2MB page size:

mmap(NULL, 6291464, PROT_NONE, MAP_PRIVATE|MAP_ANONYMOUS, -1, 0) =
0x7f11bce7f000
mmap(0x7f11bd000000, 4194312, PROT_READ|PROT_EXEC,
MAP_PRIVATE|MAP_FIXED|MAP_DENYWRITE, 3, 0) = 0x7f11bd000000

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[Bug dynamic-link/30452] LD_PREFER_MAP_32BIT_EXEC does not work with 2MiB load segment alignment

[fweimer at redhat dot com]

https://sourceware.org/bugzilla/show_bug.cgi?id=30452

--- Comment #3 from Florian Weimer <fweimer at redhat dot com> ---
The issue is that only the fast path uses MAP_DENYWRITE with a file descriptor,
and that's required for MAP_32BIT being added.

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[Bug dynamic-link/30452] LD_PREFER_MAP_32BIT_EXEC does not work with 2MiB load segment alignment

[hjl.tools at gmail dot com]

https://sourceware.org/bugzilla/show_bug.cgi?id=30452

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

           What    |Removed                     |Added
----------------------------------------------------------------------------
           Assignee|unassigned at sourceware dot org   |hjl.tools at gmail dot com

--- Comment #4 from H.J. Lu <hjl.tools at gmail dot com> ---
Created attachment 14886
  --> https://sourceware.org/bugzilla/attachment.cgi?id=14886&action=edit
A patch

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[Bug dynamic-link/30452] LD_PREFER_MAP_32BIT_EXEC does not work with 2MiB load segment alignment

[hjl.tools at gmail dot com]

https://sourceware.org/bugzilla/show_bug.cgi?id=30452

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

           What    |Removed                     |Added
----------------------------------------------------------------------------
  Attachment #14886|0                           |1
        is obsolete|                            |

--- Comment #5 from H.J. Lu <hjl.tools at gmail dot com> ---
Created attachment 14888
  --> https://sourceware.org/bugzilla/attachment.cgi?id=14888&action=edit
A patch with a testcase

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[Bug dynamic-link/30452] LD_PREFER_MAP_32BIT_EXEC does not work with 2MiB load segment alignment

[cvs-commit at gcc dot gnu.org]

https://sourceware.org/bugzilla/show_bug.cgi?id=30452

--- Comment #6 from cvs-commit at gcc dot gnu.org <cvs-commit at gcc dot gnu.org> ---
The master branch has been updated by H.J. Lu <hjl@sourceware.org>:

https://sourceware.org/git/gitweb.cgi?p=glibc.git;h=6259ab39410cdefc80077afea48ca9cb057f6005

commit 6259ab39410cdefc80077afea48ca9cb057f6005
Author: H.J. Lu <hjl.tools@gmail.com>
Date:   Thu Jun 22 14:30:31 2023 -0700

    ld.so: Always use MAP_COPY to map the first segment [BZ #30452]

    The first segment in a shared library may be read-only, not executable.
    To support LD_PREFER_MAP_32BIT_EXEC on such shared libraries, we also
    check MAP_DENYWRITE to decide if MAP_32BIT should be passed to mmap.
    Normally the first segment is mapped with MAP_COPY, which is defined
    as (MAP_PRIVATE | MAP_DENYWRITE).  But if the segment alignment is
    greater than the page size, MAP_COPY isn't used to allocate enough
    space to ensure that the segment can be properly aligned.  Map the
    first segment with MAP_COPY in this case to fix BZ #30452.

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