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[92.90.21.151]) by smtp.gmail.com with ESMTPSA id 189-v6sm10582822wmd.17.2018.07.02.11.11.58 (version=TLS1_2 cipher=ECDHE-RSA-AES128-GCM-SHA256 bits=128/128); Mon, 02 Jul 2018 11:12:00 -0700 (PDT) From: Ard Biesheuvel To: linux-arm-kernel@lists.infradead.org, linux-kernel@vger.kernel.org, linux-s390@vger.kernel.org, linux-arch@vger.kernel.org Cc: Ard Biesheuvel , Arnd Bergmann , Heiko Carstens , Kees Cook , Will Deacon , Thomas Gleixner , Catalin Marinas , Ingo Molnar , Steven Rostedt , Martin Schwidefsky , Jessica Yu , Peter Zijlstra Subject: [PATCH v2 4/8] x86: add support for 64-bit place relative relocations Date: Mon, 2 Jul 2018 20:11:41 +0200 Message-Id: <20180702181145.4799-5-ard.biesheuvel@linaro.org> X-Mailer: git-send-email 2.17.1 In-Reply-To: <20180702181145.4799-1-ard.biesheuvel@linaro.org> References: <20180702181145.4799-1-ard.biesheuvel@linaro.org> Sender: linux-kernel-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org 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 --- 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