From 78c4374ef8b842c6abf195d6f963853c7ec464d2 Mon Sep 17 00:00:00 2001 From: Ard Biesheuvel Date: Thu, 23 Jan 2025 14:07:38 -0500 Subject: [PATCH] x86/module: Deal with GOT based stack cookie load on Clang < 17 Clang versions before 17 will not honour -fdirect-access-external-data for the load of the stack cookie emitted into each function's prologue and epilogue. This is not an issue for the core kernel, as the linker will relax these loads into LEA instructions that take the address of __stack_chk_guard directly. For modules, however, we need to work around this, by dealing with R_X86_64_REX_GOTPCRELX relocations that refer to __stack_chk_guard. In this case, given that this is a GOT load, the reference should not refer to __stack_chk_guard directly, but to a memory location that holds its address. So take the address of __stack_chk_guard into a static variable, and fix up the relocations to refer to that. [ mingo: Fix broken R_X86_64_GOTPCRELX definition. ] Signed-off-by: Ard Biesheuvel Signed-off-by: Brian Gerst Signed-off-by: Ingo Molnar Cc: Linus Torvalds Link: https://lore.kernel.org/r/20250123190747.745588-7-brgerst@gmail.com --- arch/x86/include/asm/elf.h | 5 +++-- arch/x86/kernel/module.c | 15 +++++++++++++++ 2 files changed, 18 insertions(+), 2 deletions(-) diff --git a/arch/x86/include/asm/elf.h b/arch/x86/include/asm/elf.h index 1fb83d47711f9..128602612ecaa 100644 --- a/arch/x86/include/asm/elf.h +++ b/arch/x86/include/asm/elf.h @@ -54,8 +54,9 @@ typedef struct user_i387_struct elf_fpregset_t; #define R_X86_64_GLOB_DAT 6 /* Create GOT entry */ #define R_X86_64_JUMP_SLOT 7 /* Create PLT entry */ #define R_X86_64_RELATIVE 8 /* Adjust by program base */ -#define R_X86_64_GOTPCREL 9 /* 32 bit signed pc relative - offset to GOT */ +#define R_X86_64_GOTPCREL 9 /* 32 bit signed pc relative offset to GOT */ +#define R_X86_64_GOTPCRELX 41 +#define R_X86_64_REX_GOTPCRELX 42 #define R_X86_64_32 10 /* Direct 32 bit zero extended */ #define R_X86_64_32S 11 /* Direct 32 bit sign extended */ #define R_X86_64_16 12 /* Direct 16 bit zero extended */ diff --git a/arch/x86/kernel/module.c b/arch/x86/kernel/module.c index 8984abd91c001..a286f32c55036 100644 --- a/arch/x86/kernel/module.c +++ b/arch/x86/kernel/module.c @@ -19,6 +19,7 @@ #include #include #include +#include #include #include @@ -130,6 +131,20 @@ static int __write_relocate_add(Elf64_Shdr *sechdrs, goto overflow; size = 4; break; +#if defined(CONFIG_STACKPROTECTOR) && \ + defined(CONFIG_CC_IS_CLANG) && CONFIG_CLANG_VERSION < 170000 + case R_X86_64_REX_GOTPCRELX: { + static unsigned long __percpu *const addr = &__stack_chk_guard; + + if (sym->st_value != (u64)addr) { + pr_err("%s: Unsupported GOTPCREL relocation\n", me->name); + return -ENOEXEC; + } + + val = (u64)&addr + rel[i].r_addend; + fallthrough; + } +#endif case R_X86_64_PC32: case R_X86_64_PLT32: val -= (u64)loc;