Hi Andrew,
On 18/9/23 05:26, Andrew Morton wrote:
On Thu, 7 Sep 2023 11:18:08 +1000 Greg Ungerer <gerg@xxxxxxxxxx> 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@xxxxxxxxxxxxxxx>
Yes, that seems reasonable. It will apply easily, and legitimately fix this
specific issue going back to the original change.
Regards
Greg
