Messages in this thread | | | Date | Mon, 18 Sep 2023 16:27:22 +1000 | Subject | Re: [PATCH v2] fs: binfmt_elf_efpic: fix personality for ELF-FDPIC | From | Greg Ungerer <> |
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Hi Andrew,
On 18/9/23 05:26, Andrew Morton wrote: > On Thu, 7 Sep 2023 11:18:08 +1000 Greg Ungerer <gerg@kernel.org> wrote: > >> The elf-fdpic loader hard sets the process personality to either >> PER_LINUX_FDPIC for true elf-fdpic binaries or to PER_LINUX for >> normal ELF binaries (in this case they would be constant displacement >> compiled with -pie for example). The problem with that is that it >> will lose any other bits that may be in the ELF header personality >> (such as the "bug emulation" bits). >> >> On the ARM architecture the ADDR_LIMIT_32BIT flag is used to signify >> a normal 32bit binary - as opposed to a legacy 26bit address binary. >> This matters since start_thread() will set the ARM CPSR register as >> required based on this flag. If the elf-fdpic loader loses this bit >> the process will be mis-configured and crash out pretty quickly. >> >> Modify elf-fdpic loader personality setting so that it preserves the >> upper three bytes by using the SET_PERSONALITY macro to set it. This >> macro in the generic case sets PER_LINUX and preserves the upper bytes. >> Architectures can override this for their specific use case, and ARM >> does exactly this. >> >> The problem shows up quite easily running under qemu using the ARM >> architecture, but not necessarily on all types of real ARM hardware. >> If the underlying ARM processor does not support the legacy 26-bit >> addressing mode then everything will work as expected. > > I'm thinking > > Fixes: 1bde925d23547 ("fs/binfmt_elf_fdpic.c: provide NOMMU loader for regular ELF binaries") > Cc: <stable@vger.kernel.org>
Yes, that seems reasonable. It will apply easily, and legitimately fix this specific issue going back to the original change.
Regards Greg
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