libelf: Don't return unaligned data returned from elf_getdata[_rawchunk].
For i386 and x86_64 we allow some unaligned data accesses.
We also return unaligned data from elf_getdata[_rawchunk].
But that might go wrong if we then access the ELF types inside.
When build with gcc -O3 for example the compiler might vectorize
loops accessing ELF words or types. The instructions used do require
the data is naturally aligned. If the function returnes unaligned
data the program will segfault and crash. This happens for example
with the code in dwfl_module_getdwarf.c that tries to iterate over
the hash buckets gotten through elf_getdata_rawchunk based on the
DT_[GNU]_HASH value.
This only happens when the underlying ELF file is mmapped, and it
is meant as optimization so that we don't have to copy data first
so that it is correctly aligned. In most cases the data is already
naturally aligned though. But it might not be for non-native ELF
files.
Given that it might even happen in our own code base and these
are public functions that can be used by code that might rely on
the data returned being correctly aligned for the ELF data type
requested just always return correctly aligned data.
Signed-off-by: Mark Wielaard <mark@klomp.org>
4 files changed
