This is a note to let you know that I've just added the patch titled x86/build: Treat R_386_PLT32 relocation as R_386_PC32 to the 4.4-stable tree which can be found at: http://www.kernel.org/git/?p=linux/kernel/git/stable/stable-queue.git;a=summary The filename of the patch is: x86-build-treat-r_386_plt32-relocation-as-r_386_pc32.patch and it can be found in the queue-4.4 subdirectory. If you, or anyone else, feels it should not be added to the stable tree, please let <stable@xxxxxxxxxxxxxxx> know about it. commit f4eb35a321448899fc0b5c3b3e9c6ddab0478389 Author: Fangrui Song <maskray@xxxxxxxxxx> Date: Wed Jan 27 12:56:00 2021 -0800 x86/build: Treat R_386_PLT32 relocation as R_386_PC32 [ Upstream commit bb73d07148c405c293e576b40af37737faf23a6a ] This is similar to commit b21ebf2fb4cd ("x86: Treat R_X86_64_PLT32 as R_X86_64_PC32") but for i386. As far as the kernel is concerned, R_386_PLT32 can be treated the same as R_386_PC32. R_386_PLT32/R_X86_64_PLT32 are PC-relative relocation types which can only be used by branches. If the referenced symbol is defined externally, a PLT will be used. R_386_PC32/R_X86_64_PC32 are PC-relative relocation types which can be used by address taking operations and branches. If the referenced symbol is defined externally, a copy relocation/canonical PLT entry will be created in the executable. On x86-64, there is no PIC vs non-PIC PLT distinction and an R_X86_64_PLT32 relocation is produced for both `call/jmp foo` and `call/jmp foo@PLT` with newer (2018) GNU as/LLVM integrated assembler. This avoids canonical PLT entries (st_shndx=0, st_value!=0). On i386, there are 2 types of PLTs, PIC and non-PIC. Currently, the GCC/GNU as convention is to use R_386_PC32 for non-PIC PLT and R_386_PLT32 for PIC PLT. Copy relocations/canonical PLT entries are possible ABI issues but GCC/GNU as will likely keep the status quo because (1) the ABI is legacy (2) the change will drop a GNU ld diagnostic for non-default visibility ifunc in shared objects. clang-12 -fno-pic (since [1]) can emit R_386_PLT32 for compiler generated function declarations, because preventing canonical PLT entries is weighed over the rare ifunc diagnostic. Further info for the more interested: https://github.com/ClangBuiltLinux/linux/issues/1210 https://sourceware.org/bugzilla/show_bug.cgi?id=27169 https://github.com/llvm/llvm-project/commit/a084c0388e2a59b9556f2de0083333232da3f1d6 [1] [ bp: Massage commit message. ] Reported-by: Arnd Bergmann <arnd@xxxxxxxx> Signed-off-by: Fangrui Song <maskray@xxxxxxxxxx> Signed-off-by: Borislav Petkov <bp@xxxxxxx> Reviewed-by: Nick Desaulniers <ndesaulniers@xxxxxxxxxx> Reviewed-by: Nathan Chancellor <natechancellor@xxxxxxxxx> Tested-by: Nick Desaulniers <ndesaulniers@xxxxxxxxxx> Tested-by: Nathan Chancellor <natechancellor@xxxxxxxxx> Tested-by: Sedat Dilek <sedat.dilek@xxxxxxxxx> Link: https://lkml.kernel.org/r/20210127205600.1227437-1-maskray@xxxxxxxxxx Signed-off-by: Sasha Levin <sashal@xxxxxxxxxx> diff --git a/arch/x86/kernel/module.c b/arch/x86/kernel/module.c index 94779f66bf49..6f0d340594ca 100644 --- a/arch/x86/kernel/module.c +++ b/arch/x86/kernel/module.c @@ -124,6 +124,7 @@ int apply_relocate(Elf32_Shdr *sechdrs, *location += sym->st_value; break; case R_386_PC32: + case R_386_PLT32: /* Add the value, subtract its position */ *location += sym->st_value - (uint32_t)location; break; diff --git a/arch/x86/tools/relocs.c b/arch/x86/tools/relocs.c index 5b6c8486a0be..d1c3f82c7882 100644 --- a/arch/x86/tools/relocs.c +++ b/arch/x86/tools/relocs.c @@ -839,9 +839,11 @@ static int do_reloc32(struct section *sec, Elf_Rel *rel, Elf_Sym *sym, case R_386_PC32: case R_386_PC16: case R_386_PC8: + case R_386_PLT32: /* - * NONE can be ignored and PC relative relocations don't - * need to be adjusted. + * NONE can be ignored and PC relative relocations don't need + * to be adjusted. Because sym must be defined, R_386_PLT32 can + * be treated the same way as R_386_PC32. */ break; @@ -882,9 +884,11 @@ static int do_reloc_real(struct section *sec, Elf_Rel *rel, Elf_Sym *sym, case R_386_PC32: case R_386_PC16: case R_386_PC8: + case R_386_PLT32: /* - * NONE can be ignored and PC relative relocations don't - * need to be adjusted. + * NONE can be ignored and PC relative relocations don't need + * to be adjusted. Because sym must be defined, R_386_PLT32 can + * be treated the same way as R_386_PC32. */ break;