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Peter Anvin" , x86@kernel.org, Thomas Garnier , "H.J. Lu" , "Peter Zijlstra (Intel)" , Joerg Roedel , Jordan Borgner , Ard Biesheuvel , linux-kernel@vger.kernel.org Subject: [PATCH v6 17/27] x86/relocs: Handle PIE relocations Date: Thu, 31 Jan 2019 11:24:24 -0800 Message-Id: <20190131192533.34130-18-thgarnie@chromium.org> X-Mailer: git-send-email 2.20.1.495.gaa96b0ce6b-goog In-Reply-To: <20190131192533.34130-1-thgarnie@chromium.org> References: <20190131192533.34130-1-thgarnie@chromium.org> MIME-Version: 1.0 Content-Transfer-Encoding: 8bit Sender: linux-kernel-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Change the relocation tool to correctly handle relocations generated by -fPIE option: - Add relocation for each entry of the .got section given the linker does not generate R_X86_64_GLOB_DAT on a simple link. - Ignore R_X86_64_GOTPCREL. Signed-off-by: Thomas Garnier --- arch/x86/tools/relocs.c | 96 ++++++++++++++++++++++++++++++++++++++++- 1 file changed, 95 insertions(+), 1 deletion(-) diff --git a/arch/x86/tools/relocs.c b/arch/x86/tools/relocs.c index b629f6992d9f..2a3c703218cc 100644 --- a/arch/x86/tools/relocs.c +++ b/arch/x86/tools/relocs.c @@ -32,6 +32,7 @@ struct section { Elf_Sym *symtab; Elf_Rel *reltab; char *strtab; + Elf_Addr *got; }; static struct section *secs; @@ -295,6 +296,36 @@ static Elf_Sym *sym_lookup(const char *symname) return 0; } +static Elf_Sym *sym_lookup_addr(Elf_Addr addr, const char **name) +{ + int i; + + for (i = 0; i < ehdr.e_shnum; i++) { + struct section *sec = &secs[i]; + long nsyms; + Elf_Sym *symtab; + Elf_Sym *sym; + + if (sec->shdr.sh_type != SHT_SYMTAB) + continue; + + nsyms = sec->shdr.sh_size/sizeof(Elf_Sym); + symtab = sec->symtab; + + for (sym = symtab; --nsyms >= 0; sym++) { + if (sym->st_value == addr) { + if (name) { + *name = sym_name(sec->link->strtab, + sym); + } + return sym; + } + } + } + return 0; +} + + #if BYTE_ORDER == LITTLE_ENDIAN #define le16_to_cpu(val) (val) #define le32_to_cpu(val) (val) @@ -515,6 +546,35 @@ static void read_relocs(FILE *fp) } } +static void read_got(FILE *fp) +{ + int i; + + for (i = 0; i < ehdr.e_shnum; i++) { + struct section *sec = &secs[i]; + + sec->got = NULL; + if (sec->shdr.sh_type != SHT_PROGBITS || + strcmp(sec_name(i), ".got")) { + continue; + } + sec->got = malloc(sec->shdr.sh_size); + if (!sec->got) { + die("malloc of %d bytes for got failed\n", + sec->shdr.sh_size); + } + if (fseek(fp, sec->shdr.sh_offset, SEEK_SET) < 0) { + die("Seek to %d failed: %s\n", + sec->shdr.sh_offset, strerror(errno)); + } + if (fread(sec->got, 1, sec->shdr.sh_size, fp) + != sec->shdr.sh_size) { + die("Cannot read got: %s\n", + strerror(errno)); + } + } +} + static void print_absolute_symbols(void) { @@ -645,6 +705,32 @@ static void add_reloc(struct relocs *r, uint32_t offset) r->offset[r->count++] = offset; } +/* + * The linker does not generate relocations for the GOT for the kernel. + * If a GOT is found, simulate the relocations that should have been included. + */ +static void walk_got_table(int (*process)(struct section *sec, Elf_Rel *rel, + Elf_Sym *sym, const char *symname), + struct section *sec) +{ + int i; + Elf_Addr entry; + Elf_Sym *sym; + const char *symname; + Elf_Rel rel; + + for (i = 0; i < sec->shdr.sh_size/sizeof(Elf_Addr); i++) { + entry = sec->got[i]; + sym = sym_lookup_addr(entry, &symname); + if (!sym) + die("Could not found got symbol for entry %d\n", i); + rel.r_offset = sec->shdr.sh_addr + i * sizeof(Elf_Addr); + rel.r_info = ELF_BITS == 64 ? R_X86_64_GLOB_DAT + : R_386_GLOB_DAT; + process(sec, &rel, sym, symname); + } +} + static void walk_relocs(int (*process)(struct section *sec, Elf_Rel *rel, Elf_Sym *sym, const char *symname)) { @@ -658,6 +744,8 @@ static void walk_relocs(int (*process)(struct section *sec, Elf_Rel *rel, struct section *sec = &secs[i]; if (sec->shdr.sh_type != SHT_REL_TYPE) { + if (sec->got) + walk_got_table(process, sec); continue; } sec_symtab = sec->link; @@ -767,6 +855,7 @@ static int do_reloc64(struct section *sec, Elf_Rel *rel, ElfW(Sym) *sym, offset += per_cpu_load_addr; switch (r_type) { + case R_X86_64_GOTPCREL: case R_X86_64_NONE: /* NONE can be ignored. */ break; @@ -820,7 +909,7 @@ static int do_reloc64(struct section *sec, Elf_Rel *rel, ElfW(Sym) *sym, * the relocations are processed. * Make sure that the offset will fit. */ - if ((int32_t)offset != (int64_t)offset) + if (r_type != R_X86_64_64 && (int32_t)offset != (int64_t)offset) die("Relocation offset doesn't fit in 32 bits\n"); if (r_type == R_X86_64_64) @@ -829,6 +918,10 @@ static int do_reloc64(struct section *sec, Elf_Rel *rel, ElfW(Sym) *sym, add_reloc(&relocs32, offset); break; + case R_X86_64_GLOB_DAT: + add_reloc(&relocs64, offset); + break; + default: die("Unsupported relocation type: %s (%d)\n", rel_type(r_type), r_type); @@ -1098,6 +1191,7 @@ void process(FILE *fp, int use_real_mode, int as_text, read_strtabs(fp); read_symtabs(fp); read_relocs(fp); + read_got(fp); if (ELF_BITS == 64) percpu_init(); if (show_absolute_syms) { -- 2.20.1.495.gaa96b0ce6b-goog