[Bug dynamic-link/20480] Patch: ifunc not executable, crashes sudo qemu

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https://sourceware.org/bugzilla/show_bug.cgi?id=20480

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https://sourceware.org/git/gitweb.cgi?p=glibc.git;h=b5c45e83753b27dc538dff2d55d4410c385cf3a4

commit b5c45e83753b27dc538dff2d55d4410c385cf3a4
Author: Adhemerval Zanella <adhemerval.zanella@linaro.org>
Date:   Mon Aug 27 16:16:43 2018 -0300

    Fix ifunc support with DT_TEXTREL segments (BZ#20480)

    Currently, DT_TEXTREL is incompatible with IFUNC.  When DT_TEXTREL or
    DF_TEXTREL is seen, the dynamic linker calls __mprotect on the segments
    with PROT_READ|PROT_WRITE before applying dynamic relocations. It leads
    to segfault when performing IFUNC resolution (which requires PROT_EXEC
    as well for the IFUNC resolver).

    This patch makes it call __mprotect with extra PROT_WRITE bit, which
    will keep the PROT_EXEC bit if exists, and thus fixes the segfault.
    FreeBSD rtld libexec/rtld-elf/rtld.c (reloc_textrel_prot) does the same.

    Checked on x86_64-linux-gnu, i686-linux-gnu, aarch64-linux-gnu,
    sparc64-linux-gnu, sparcv9-linux-gnu, and armv8-linux-gnueabihf.

        Adam J. Richte  <adam_richter2004@yahoo.com>
        Adhemerval Zanella  <adhemerval.zanella@linaro.org>
        Fangrui Song  <maskray@google.com>

        [BZ #20480]
        * config.h.in (CAN_TEXTREL_IFUNC): New define.
        * configure.ac: Add check if linker supports textrel relocation with
        ifunc.
        * elf/dl-reloc.c (_dl_relocate_object): Use all required flags on
        DT_TEXTREL segments, not only PROT_READ and PROT_WRITE.
        * elf/Makefile (ifunc-pie-tests): Add tst-ifunc-textrel.
        (CFLAGS-tst-ifunc-textrel.c): New rule.
        * elf/tst-ifunc-textrel.c: New file.

-----------------------------------------------------------------------

Summary of changes:
 ChangeLog                                          |   15 ++++++
 config.make.in                                     |    1 +
 configure                                          |   47 ++++++++++++++++++++
 configure.ac                                       |   35 +++++++++++++++
 elf/Makefile                                       |    4 ++
 elf/dl-reloc.c                                     |   20 +++-----
 .../tst-cet-legacy-3.c => elf/tst-ifunc-textrel.c  |   28 ++++++++----
 7 files changed, 128 insertions(+), 22 deletions(-)
 copy sysdeps/x86/tst-cet-legacy-3.c => elf/tst-ifunc-textrel.c (66%)

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