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- From ab7647c2b04501297c50ce7cdb6f6895b9582d22 Mon Sep 17 00:00:00 2001
- From: Greg Ungerer <gerg@kernel.org>
- Date: Fri, 21 Apr 2023 00:21:38 +1000
- Subject: [PATCH] fs: binfmt_elf_efpic: fix personality for fdpic ELF
- 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 loaders personality setting binaries 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 runing under qemu, 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 everyting will work
- as expected.
- Signed-off-by: Greg Ungerer <gerg@kernel.org>
- ---
- fs/binfmt_elf_fdpic.c | 5 ++---
- 1 file changed, 2 insertions(+), 3 deletions(-)
- diff --git a/fs/binfmt_elf_fdpic.c b/fs/binfmt_elf_fdpic.c
- index a05eafcacfb2..f29ae1d96fd7 100644
- --- a/fs/binfmt_elf_fdpic.c
- +++ b/fs/binfmt_elf_fdpic.c
- @@ -345,10 +345,9 @@
- /* 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;
-
- --
- 2.25.1
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