This adds support for emitting PLTs at module load time for relative branches that are out of range. This is a prerequisite for KASLR, which may place the kernel and the modules anywhere in the vmalloc area, making it likely that branch target offsets exceed the maximum range of +/- 128 MB.
Signed-off-by: Ard Biesheuvel <[email protected]> --- arch/arm64/Kconfig | 4 + arch/arm64/Makefile | 4 + arch/arm64/include/asm/module.h | 11 ++ arch/arm64/kernel/Makefile | 1 + arch/arm64/kernel/module-plts.c | 137 ++++++++++++++++++++ arch/arm64/kernel/module.c | 7 + arch/arm64/kernel/module.lds | 4 + 7 files changed, 168 insertions(+) diff --git a/arch/arm64/Kconfig b/arch/arm64/Kconfig index 871f21783866..827e78f33944 100644 --- a/arch/arm64/Kconfig +++ b/arch/arm64/Kconfig @@ -704,6 +704,10 @@ config ARM64_LSE_ATOMICS endmenu +config ARM64_MODULE_PLTS + bool + select HAVE_MOD_ARCH_SPECIFIC + endmenu menu "Boot options" diff --git a/arch/arm64/Makefile b/arch/arm64/Makefile index cd822d8454c0..d4654830e536 100644 --- a/arch/arm64/Makefile +++ b/arch/arm64/Makefile @@ -45,6 +45,10 @@ ifeq ($(CONFIG_ARM64_ERRATUM_843419), y) KBUILD_CFLAGS_MODULE += -mcmodel=large endif +ifeq ($(CONFIG_ARM64_MODULE_PLTS),y) +KBUILD_LDFLAGS_MODULE += -T $(srctree)/arch/arm64/kernel/module.lds +endif + # Default value head-y := arch/arm64/kernel/head.o diff --git a/arch/arm64/include/asm/module.h b/arch/arm64/include/asm/module.h index e80e232b730e..7b8cd3dc9d8e 100644 --- a/arch/arm64/include/asm/module.h +++ b/arch/arm64/include/asm/module.h @@ -20,4 +20,15 @@ #define MODULE_ARCH_VERMAGIC "aarch64" +#ifdef CONFIG_ARM64_MODULE_PLTS +struct mod_arch_specific { + struct elf64_shdr *core_plt; + struct elf64_shdr *init_plt; + int core_plt_count; + int init_plt_count; +}; +#endif + +u64 get_module_plt(struct module *mod, void *loc, u64 val); + #endif /* __ASM_MODULE_H */ diff --git a/arch/arm64/kernel/Makefile b/arch/arm64/kernel/Makefile index 474691f8b13a..f42b0fff607f 100644 --- a/arch/arm64/kernel/Makefile +++ b/arch/arm64/kernel/Makefile @@ -30,6 +30,7 @@ arm64-obj-$(CONFIG_COMPAT) += sys32.o kuser32.o signal32.o \ ../../arm/kernel/opcodes.o arm64-obj-$(CONFIG_FUNCTION_TRACER) += ftrace.o entry-ftrace.o arm64-obj-$(CONFIG_MODULES) += arm64ksyms.o module.o +arm64-obj-$(CONFIG_ARM64_MODULE_PLTS) += module-plts.o arm64-obj-$(CONFIG_PERF_EVENTS) += perf_regs.o perf_callchain.o arm64-obj-$(CONFIG_HW_PERF_EVENTS) += perf_event.o arm64-obj-$(CONFIG_HAVE_HW_BREAKPOINT) += hw_breakpoint.o diff --git a/arch/arm64/kernel/module-plts.c b/arch/arm64/kernel/module-plts.c new file mode 100644 index 000000000000..4a8ef9ea01ee --- /dev/null +++ b/arch/arm64/kernel/module-plts.c @@ -0,0 +1,137 @@ +/* + * Copyright (C) 2014-2015 Linaro Ltd. <[email protected]> + * + * This program is free software; you can redistribute it and/or modify + * it under the terms of the GNU General Public License version 2 as + * published by the Free Software Foundation. + */ + +#include <linux/elf.h> +#include <linux/kernel.h> +#include <linux/module.h> + +struct plt_entry { + __le32 mov0; /* movn x16, #0x.... */ + __le32 mov1; /* movk x16, #0x...., lsl #16 */ + __le32 mov2; /* movk x16, #0x...., lsl #32 */ + __le32 br; /* br x16 */ +} __aligned(8); + +static bool in_init(const struct module *mod, void *addr) +{ + return (u64)addr - (u64)mod->module_init < mod->init_size; +} + +u64 get_module_plt(struct module *mod, void *loc, u64 val) +{ + struct plt_entry entry = { + cpu_to_le32(0x92800010 | (((~val ) & 0xffff)) << 5), + cpu_to_le32(0xf2a00010 | ((( val >> 16) & 0xffff)) << 5), + cpu_to_le32(0xf2c00010 | ((( val >> 32) & 0xffff)) << 5), + cpu_to_le32(0xd61f0200) + }, *plt; + int i, *count; + + if (in_init(mod, loc)) { + plt = (struct plt_entry *)mod->arch.init_plt->sh_addr; + count = &mod->arch.init_plt_count; + } else { + plt = (struct plt_entry *)mod->arch.core_plt->sh_addr; + count = &mod->arch.core_plt_count; + } + + /* Look for an existing entry pointing to 'val' */ + for (i = 0; i < *count; i++) + if (plt[i].mov0 == entry.mov0 && + plt[i].mov1 == entry.mov1 && + plt[i].mov2 == entry.mov2) + return (u64)&plt[i]; + + i = (*count)++; + plt[i] = entry; + return (u64)&plt[i]; +} + +static int duplicate_rel(Elf64_Addr base, const Elf64_Rela *rela, int num) +{ + int i; + + for (i = 0; i < num; i++) { + if (rela[i].r_info == rela[num].r_info && + rela[i].r_addend == rela[num].r_addend) + return 1; + } + return 0; +} + +/* Count how many PLT entries we may need */ +static unsigned int count_plts(Elf64_Addr base, const Elf64_Rela *rela, int num) +{ + unsigned int ret = 0; + int i; + + /* + * Sure, this is order(n^2), but it's usually short, and not + * time critical + */ + for (i = 0; i < num; i++) + switch (ELF64_R_TYPE(rela[i].r_info)) { + case R_AARCH64_JUMP26: + case R_AARCH64_CALL26: + if (!duplicate_rel(base, rela, i)) + ret++; + break; + } + return ret; +} + +int module_frob_arch_sections(Elf_Ehdr *ehdr, Elf_Shdr *sechdrs, + char *secstrings, struct module *mod) +{ + unsigned long core_plts = 0, init_plts = 0; + Elf64_Shdr *s, *sechdrs_end = sechdrs + ehdr->e_shnum; + + /* + * To store the PLTs, we expand the .text section for core module code + * and the .init.text section for initialization code. + */ + for (s = sechdrs; s < sechdrs_end; ++s) + if (strcmp(".core.plt", secstrings + s->sh_name) == 0) + mod->arch.core_plt = s; + else if (strcmp(".init.plt", secstrings + s->sh_name) == 0) + mod->arch.init_plt = s; + + if (!mod->arch.core_plt || !mod->arch.init_plt) { + pr_err("%s: sections missing\n", mod->name); + return -ENOEXEC; + } + + for (s = sechdrs + 1; s < sechdrs_end; ++s) { + const Elf64_Rela *rels = (void *)ehdr + s->sh_offset; + int numrels = s->sh_size / sizeof(Elf64_Rela); + Elf64_Shdr *dstsec = sechdrs + s->sh_info; + + if (s->sh_type != SHT_RELA) + continue; + + if (strstr(secstrings + s->sh_name, ".init")) + init_plts += count_plts(dstsec->sh_addr, rels, numrels); + else + core_plts += count_plts(dstsec->sh_addr, rels, numrels); + } + + mod->arch.core_plt->sh_type = SHT_NOBITS; + mod->arch.core_plt->sh_flags = SHF_EXECINSTR | SHF_ALLOC; + mod->arch.core_plt->sh_addralign = L1_CACHE_BYTES; + mod->arch.core_plt->sh_size = core_plts * sizeof(struct plt_entry); + mod->arch.core_plt_count = 0; + + mod->arch.init_plt->sh_type = SHT_NOBITS; + mod->arch.init_plt->sh_flags = SHF_EXECINSTR | SHF_ALLOC; + mod->arch.init_plt->sh_addralign = L1_CACHE_BYTES; + mod->arch.init_plt->sh_size = init_plts * sizeof(struct plt_entry); + mod->arch.init_plt_count = 0; + pr_debug("%s: core.plt=%lld, init.plt=%lld\n", __func__, + mod->arch.core_plt->sh_size, mod->arch.init_plt->sh_size); + return 0; +} diff --git a/arch/arm64/kernel/module.c b/arch/arm64/kernel/module.c index f4bc779e62e8..14880d77ec6f 100644 --- a/arch/arm64/kernel/module.c +++ b/arch/arm64/kernel/module.c @@ -388,6 +388,13 @@ int apply_relocate_add(Elf64_Shdr *sechdrs, case R_AARCH64_CALL26: ovf = reloc_insn_imm(RELOC_OP_PREL, loc, val, 2, 26, AARCH64_INSN_IMM_26); + + if (IS_ENABLED(CONFIG_ARM64_MODULE_PLTS) && + ovf == -ERANGE) { + val = get_module_plt(me, loc, val); + ovf = reloc_insn_imm(RELOC_OP_PREL, loc, val, 2, + 26, AARCH64_INSN_IMM_26); + } break; default: diff --git a/arch/arm64/kernel/module.lds b/arch/arm64/kernel/module.lds new file mode 100644 index 000000000000..3682fa107918 --- /dev/null +++ b/arch/arm64/kernel/module.lds @@ -0,0 +1,4 @@ +SECTIONS { + .core.plt : { BYTE(0) } + .init.plt : { BYTE(0) } +} -- 2.5.0 -- To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to [email protected] More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/
