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@@ -1,42 +1,51 @@
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From ab7647c2b04501297c50ce7cdb6f6895b9582d22 Mon Sep 17 00:00:00 2001
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From: Greg Ungerer <gerg@kernel.org>
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Date: Fri, 21 Apr 2023 00:21:38 +1000
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-Subject: [PATCH] fs: binfmt_elf_efpic: fix personality for non-fdpic ELF
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+Subject: [PATCH] fs: binfmt_elf_efpic: fix personality for fdpic ELF
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The elf-fdpic loader hard sets the process personality to either
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PER_LINUX_FDPIC for true elf-fdpic binaries or to PER_LINUX for
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normal ELF binaries (in this case they would be constant displacement
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compiled with -pie for example). The problem with that is that it
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will lose any other bits that may be in the ELF header personality
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-("the "bug emulation" bits).
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+(such as the "bug emulation" bits).
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On the ARM architecture the ADDR_LIMIT_32BIT flag is used to signify
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a normal 32bit binary - as opposed to a legacy 26bit address binary.
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This matters since start_thread() will set the ARM CPSR register as
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-required based on this flag. If the elf-fdpic loader has lost this
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-bit the process will be mis-configured and crash out pretty quickly.
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+required based on this flag. If the elf-fdpic loader loses this bit
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+the process will be mis-configured and crash out pretty quickly.
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-Modify elf-fdpic loaders personality setting for ELF binaries so that
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-it preserves the upper three bytes by using the SET_PERSONALITY macro
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-to set it. This macro in the generic case sets PER_LINUX but and
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-preserves the upper bytes. Architectures can override this for their
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-specific use case, and ARM does exactly this.
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+Modify elf-fdpic loaders personality setting binaries so that it
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+preserves the upper three bytes by using the SET_PERSONALITY macro
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+to set it. This macro in the generic case sets PER_LINUX and preserves
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+the upper bytes. Architectures can override this for their specific
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+use case, and ARM does exactly this.
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+
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+The problem shows up quite easily runing under qemu, but not necessarily
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+on all types of real ARM hardware. If the underlying ARM processor does
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+not support the legacy 26-bit addressing mode then everyting will work
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+as expected.
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Signed-off-by: Greg Ungerer <gerg@kernel.org>
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---
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- fs/binfmt_elf_fdpic.c | 2 +-
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- 1 file changed, 1 insertion(+), 1 deletion(-)
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+ fs/binfmt_elf_fdpic.c | 5 ++---
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+ 1 file changed, 2 insertions(+), 3 deletions(-)
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diff --git a/fs/binfmt_elf_fdpic.c b/fs/binfmt_elf_fdpic.c
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index a05eafcacfb2..f29ae1d96fd7 100644
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--- a/fs/binfmt_elf_fdpic.c
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+++ b/fs/binfmt_elf_fdpic.c
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-@@ -348,7 +348,7 @@ static int load_elf_fdpic_binary(struct linux_binprm *bprm)
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+@@ -345,10 +345,9 @@
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+ /* there's now no turning back... the old userspace image is dead,
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+ * defunct, deceased, etc.
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+ */
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++ SET_PERSONALITY(exec_params.hdr);
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if (elf_check_fdpic(&exec_params.hdr))
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- set_personality(PER_LINUX_FDPIC);
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- else
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+- set_personality(PER_LINUX_FDPIC);
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+- else
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- set_personality(PER_LINUX);
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-+ SET_PERSONALITY(exec_params.hdr);
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++ current->personality |= PER_LINUX_FDPIC;
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if (elf_read_implies_exec(&exec_params.hdr, executable_stack))
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current->personality |= READ_IMPLIES_EXEC;
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Waldemar Brodkorb