[PATCH v2 4/8] x86: add support for 64-bit place relative relocations
From: Ard Biesheuvel <hidden>
Date: 2018-07-02 18:12:10
Also in:
linux-arch, linux-s390, lkml
Subsystem:
the rest, x86 architecture (32-bit and 64-bit) · Maintainers:
Linus Torvalds, Thomas Gleixner, Ingo Molnar, Borislav Petkov, Dave Hansen
Add support for R_X86_64_PC64 relocations, which operate on 64-bit quantities holding a relative symbol reference. This allows jump table entries to be emitted in a way that makes them invariant under runtime relocation, which means that no metadata needs to be emitted into the kernel image to describe such data structures, resulting in a size reduction. Signed-off-by: Ard Biesheuvel <redacted> --- arch/x86/include/asm/elf.h | 1 + arch/x86/kernel/machine_kexec_64.c | 4 ++++ arch/x86/kernel/module.c | 6 ++++++ arch/x86/tools/relocs.c | 10 ++++++++++ 4 files changed, 21 insertions(+)
diff --git a/arch/x86/include/asm/elf.h b/arch/x86/include/asm/elf.h
index 0d157d2a1e2a..d3925d684296 100644
--- a/arch/x86/include/asm/elf.h
+++ b/arch/x86/include/asm/elf.h@@ -62,6 +62,7 @@ typedef struct user_fxsr_struct elf_fpxregset_t; #define R_X86_64_PC16 13 /* 16 bit sign extended pc relative */ #define R_X86_64_8 14 /* Direct 8 bit sign extended */ #define R_X86_64_PC8 15 /* 8 bit sign extended pc relative */ +#define R_X86_64_PC64 24 /* Place relative 64-bit signed */ #define R_X86_64_NUM 16
diff --git a/arch/x86/kernel/machine_kexec_64.c b/arch/x86/kernel/machine_kexec_64.c
index 4c8acdfdc5a7..6638d1edb2be 100644
--- a/arch/x86/kernel/machine_kexec_64.c
+++ b/arch/x86/kernel/machine_kexec_64.c@@ -496,6 +496,10 @@ int arch_kexec_apply_relocations_add(struct purgatory_info *pi, value -= (u64)address; *(u32 *)location = value; break; + case R_X86_64_PC64: + value -= (u64)address; + *(u64 *)location = value; + break; default: pr_err("Unknown rela relocation: %llu\n", ELF64_R_TYPE(rel[i].r_info));
diff --git a/arch/x86/kernel/module.c b/arch/x86/kernel/module.c
index f58336af095c..b052e883dd8c 100644
--- a/arch/x86/kernel/module.c
+++ b/arch/x86/kernel/module.c@@ -201,6 +201,12 @@ int apply_relocate_add(Elf64_Shdr *sechdrs, goto overflow; #endif break; + case R_X86_64_PC64: + if (*(u64 *)loc != 0) + goto invalid_relocation; + val -= (u64)loc; + *(u64 *)loc = val; + break; default: pr_err("%s: Unknown rela relocation: %llu\n", me->name, ELF64_R_TYPE(rel[i].r_info));
diff --git a/arch/x86/tools/relocs.c b/arch/x86/tools/relocs.c
index 220e97841e49..a4075bc37e8f 100644
--- a/arch/x86/tools/relocs.c
+++ b/arch/x86/tools/relocs.c@@ -195,6 +195,7 @@ static const char *rel_type(unsigned type) #if ELF_BITS == 64 REL_TYPE(R_X86_64_NONE), REL_TYPE(R_X86_64_64), + REL_TYPE(R_X86_64_PC64), REL_TYPE(R_X86_64_PC32), REL_TYPE(R_X86_64_GOT32), REL_TYPE(R_X86_64_PLT32),
@@ -781,6 +782,15 @@ static int do_reloc64(struct section *sec, Elf_Rel *rel, ElfW(Sym) *sym, add_reloc(&relocs32neg, offset); break; + case R_X86_64_PC64: + /* + * Only used by jump labels + */ + if (is_percpu_sym(sym, symname)) + die("Invalid R_X86_64_PC64 relocation against per-CPU symbol %s\n", + symname); + break; + case R_X86_64_32: case R_X86_64_32S: case R_X86_64_64:
--
2.17.1