4.19-stable review patch. If anyone has any objections, please let me know.
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From: Greg Ungerer gerg@kernel.org
commit 7c3151585730b7095287be8162b846d31e6eee61 upstream.
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.
Link: https://lkml.kernel.org/r/20230907011808.2985083-1-gerg@kernel.org Fixes: 1bde925d23547 ("fs/binfmt_elf_fdpic.c: provide NOMMU loader for regular ELF binaries") Signed-off-by: Greg Ungerer gerg@kernel.org Cc: Al Viro viro@zeniv.linux.org.uk Cc: Christian Brauner brauner@kernel.org Cc: Eric W. Biederman ebiederm@xmission.com Cc: Greg Ungerer gerg@kernel.org Cc: Kees Cook keescook@chromium.org Cc: stable@vger.kernel.org Signed-off-by: Andrew Morton akpm@linux-foundation.org Signed-off-by: Greg Kroah-Hartman gregkh@linuxfoundation.org --- fs/binfmt_elf_fdpic.c | 5 ++--- 1 file changed, 2 insertions(+), 3 deletions(-)
--- a/fs/binfmt_elf_fdpic.c +++ b/fs/binfmt_elf_fdpic.c @@ -349,10 +349,9 @@ static int load_elf_fdpic_binary(struct /* there's now no turning back... the old userspace image is dead, * defunct, deceased, etc. */ + SET_PERSONALITY(exec_params.hdr); if (elf_check_fdpic(&exec_params.hdr)) - set_personality(PER_LINUX_FDPIC); - else - set_personality(PER_LINUX); + current->personality |= PER_LINUX_FDPIC; if (elf_read_implies_exec(&exec_params.hdr, executable_stack)) current->personality |= READ_IMPLIES_EXEC;