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elf: Fix GL(dl_phdr) and GL(dl_phnum) for static builds [BZ #29864]
The 73fc4e28b9
refactor did not add the GL(dl_phdr) and
GL(dl_phnum) for static build, relying on the __ehdr_start symbol,
which is always added by the static linker, to get the correct values.
This is problematic in some ways:
- The segment may see its in-memory size differ from its in-file
size (or the binary may have holes). The Linux has fixed is to
provide concise values for both AT_PHDR and AT_PHNUM (commit
0da1d5002745c - "fs/binfmt_elf: Fix AT_PHDR for unusual ELF files")
- Some archs (alpha for instance) the hidden weak reference is not
correctly pulled by the static linker and __ehdr_start address
end up being 0, which makes GL(dl_phdr) and GL(dl_phnum) have both
invalid values (and triggering a segfault later on libc.so while
accessing TLS variables).
The safer fix is to just restore the previous behavior to setup
GL(dl_phdr) and GL(dl_phnum) for static based on kernel auxv. The
__ehdr_start fallback can also be simplified by not assuming weak
linkage (as for PIE).
The libc-static.c auxv init logic is moved to dl-support.c, since
the later is build without SHARED and then GLRO macro is defined
to access the variables directly.
The _dl_phdr is also assumed to be always non NULL, since an invalid
NULL values does not trigger TLS initialization (which is used in
various libc systems).
Checked on aarch64-linux-gnu, x86_64-linux-gnu, and i686-linux-gnu.
Reviewed-by: Florian Weimer <fweimer@redhat.com>
This commit is contained in:
parent
402853be1d
commit
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@ -262,28 +262,7 @@ LIBC_START_MAIN (int (*main) (int, char **, char ** MAIN_AUXVEC_DECL),
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}
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# endif
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_dl_aux_init (auxvec);
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if (GL(dl_phdr) == NULL)
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# endif
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{
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/* Starting from binutils-2.23, the linker will define the
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magic symbol __ehdr_start to point to our own ELF header
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if it is visible in a segment that also includes the phdrs.
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So we can set up _dl_phdr and _dl_phnum even without any
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information from auxv. */
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extern const ElfW(Ehdr) __ehdr_start
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# if BUILD_PIE_DEFAULT
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__attribute__ ((visibility ("hidden")));
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# else
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__attribute__ ((weak, visibility ("hidden")));
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if (&__ehdr_start != NULL)
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# endif
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{
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assert (__ehdr_start.e_phentsize == sizeof *GL(dl_phdr));
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GL(dl_phdr) = (const void *) &__ehdr_start + __ehdr_start.e_phoff;
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GL(dl_phnum) = __ehdr_start.e_phnum;
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}
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}
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__tunables_init (__environ);
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@ -119,7 +119,6 @@ __libc_setup_tls (void)
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__tls_pre_init_tp ();
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/* Look through the TLS segment if there is any. */
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if (_dl_phdr != NULL)
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for (phdr = _dl_phdr; phdr < &_dl_phdr[_dl_phnum]; ++phdr)
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if (phdr->p_type == PT_TLS)
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{
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@ -256,6 +256,25 @@ _dl_aux_init (ElfW(auxv_t) *av)
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for (int i = 0; i < array_length (auxv_values); ++i)
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auxv_values[i] = 0;
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_dl_parse_auxv (av, auxv_values);
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_dl_phdr = (void*) auxv_values[AT_PHDR];
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_dl_phnum = auxv_values[AT_PHNUM];
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if (_dl_phdr == NULL)
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{
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/* Starting from binutils-2.23, the linker will define the
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magic symbol __ehdr_start to point to our own ELF header
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if it is visible in a segment that also includes the phdrs.
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So we can set up _dl_phdr and _dl_phnum even without any
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information from auxv. */
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extern const ElfW(Ehdr) __ehdr_start attribute_hidden;
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assert (__ehdr_start.e_phentsize == sizeof *GL(dl_phdr));
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_dl_phdr = (const void *) &__ehdr_start + __ehdr_start.e_phoff;
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_dl_phnum = __ehdr_start.e_phnum;
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}
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assert (_dl_phdr != NULL);
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}
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#endif
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@ -324,7 +343,6 @@ _dl_non_dynamic_init (void)
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if (_dl_platform != NULL)
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_dl_platformlen = strlen (_dl_platform);
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if (_dl_phdr != NULL)
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for (const ElfW(Phdr) *ph = _dl_phdr; ph < &_dl_phdr[_dl_phnum]; ++ph)
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switch (ph->p_type)
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{
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