diff options
| -rw-r--r-- | arch/arm64/Kconfig | 9 | ||||
| -rw-r--r-- | arch/arm64/Makefile | 6 | ||||
| -rw-r--r-- | arch/arm64/include/asm/module.h | 11 | ||||
| -rw-r--r-- | arch/arm64/kernel/Makefile | 1 | ||||
| -rw-r--r-- | arch/arm64/kernel/module-plts.c | 201 | ||||
| -rw-r--r-- | arch/arm64/kernel/module.c | 22 | ||||
| -rw-r--r-- | arch/arm64/kernel/module.lds | 3 |
7 files changed, 252 insertions, 1 deletions
diff --git a/arch/arm64/Kconfig b/arch/arm64/Kconfig index cfa1cc9..c85c29d 100644 --- a/arch/arm64/Kconfig +++ b/arch/arm64/Kconfig @@ -395,6 +395,7 @@ config ARM64_ERRATUM_843419 bool "Cortex-A53: 843419: A load or store might access an incorrect address" depends on MODULES default y + select ARM64_MODULE_CMODEL_LARGE help This option builds kernel modules using the large memory model in order to avoid the use of the ADRP instruction, which can cause @@ -778,6 +779,14 @@ config ARM64_UAO regular load/store instructions if the cpu does not implement the feature. +config ARM64_MODULE_CMODEL_LARGE + bool + +config ARM64_MODULE_PLTS + bool + select ARM64_MODULE_CMODEL_LARGE + select HAVE_MOD_ARCH_SPECIFIC + endmenu menu "Boot options" diff --git a/arch/arm64/Makefile b/arch/arm64/Makefile index 307237c..a6bba96 100644 --- a/arch/arm64/Makefile +++ b/arch/arm64/Makefile @@ -43,10 +43,14 @@ endif CHECKFLAGS += -D__aarch64__ -ifeq ($(CONFIG_ARM64_ERRATUM_843419), y) +ifeq ($(CONFIG_ARM64_MODULE_CMODEL_LARGE), y) KBUILD_CFLAGS_MODULE += -mcmodel=large endif +ifeq ($(CONFIG_ARM64_MODULE_PLTS),y) +KBUILD_LDFLAGS_MODULE += -T $(srctree)/arch/arm64/kernel/module.lds +endif + # Default value head-y := arch/arm64/kernel/head.o diff --git a/arch/arm64/include/asm/module.h b/arch/arm64/include/asm/module.h index e80e232..8652fb6 100644 --- a/arch/arm64/include/asm/module.h +++ b/arch/arm64/include/asm/module.h @@ -20,4 +20,15 @@ #define MODULE_ARCH_VERMAGIC "aarch64" +#ifdef CONFIG_ARM64_MODULE_PLTS +struct mod_arch_specific { + struct elf64_shdr *plt; + int plt_num_entries; + int plt_max_entries; +}; +#endif + +u64 module_emit_plt_entry(struct module *mod, const Elf64_Rela *rela, + Elf64_Sym *sym); + #endif /* __ASM_MODULE_H */ diff --git a/arch/arm64/kernel/Makefile b/arch/arm64/kernel/Makefile index 8a9c65c..9ca2a48 100644 --- a/arch/arm64/kernel/Makefile +++ b/arch/arm64/kernel/Makefile @@ -30,6 +30,7 @@ arm64-obj-$(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 0000000..1ce90d8 --- /dev/null +++ b/arch/arm64/kernel/module-plts.c @@ -0,0 +1,201 @@ +/* + * Copyright (C) 2014-2016 Linaro Ltd. <ard.biesheuvel@linaro.org> + * + * 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> +#include <linux/sort.h> + +struct plt_entry { + /* + * A program that conforms to the AArch64 Procedure Call Standard + * (AAPCS64) must assume that a veneer that alters IP0 (x16) and/or + * IP1 (x17) may be inserted at any branch instruction that is + * exposed to a relocation that supports long branches. Since that + * is exactly what we are dealing with here, we are free to use x16 + * as a scratch register in the PLT veneers. + */ + __le32 mov0; /* movn x16, #0x.... */ + __le32 mov1; /* movk x16, #0x...., lsl #16 */ + __le32 mov2; /* movk x16, #0x...., lsl #32 */ + __le32 br; /* br x16 */ +}; + +u64 module_emit_plt_entry(struct module *mod, const Elf64_Rela *rela, + Elf64_Sym *sym) +{ + struct plt_entry *plt = (struct plt_entry *)mod->arch.plt->sh_addr; + int i = mod->arch.plt_num_entries; + u64 val = sym->st_value + rela->r_addend; + + /* + * We only emit PLT entries against undefined (SHN_UNDEF) symbols, + * which are listed in the ELF symtab section, but without a type + * or a size. + * So, similar to how the module loader uses the Elf64_Sym::st_value + * field to store the resolved addresses of undefined symbols, let's + * borrow the Elf64_Sym::st_size field (whose value is never used by + * the module loader, even for symbols that are defined) to record + * the address of a symbol's associated PLT entry as we emit it for a + * zero addend relocation (which is the only kind we have to deal with + * in practice). This allows us to find duplicates without having to + * go through the table every time. + */ + if (rela->r_addend == 0 && sym->st_size != 0) { + BUG_ON(sym->st_size < (u64)plt || sym->st_size >= (u64)&plt[i]); + return sym->st_size; + } + + mod->arch.plt_num_entries++; + BUG_ON(mod->arch.plt_num_entries > mod->arch.plt_max_entries); + + /* + * MOVK/MOVN/MOVZ opcode: + * +--------+------------+--------+-----------+-------------+---------+ + * | sf[31] | opc[30:29] | 100101 | hw[22:21] | imm16[20:5] | Rd[4:0] | + * +--------+------------+--------+-----------+-------------+---------+ + * + * Rd := 0x10 (x16) + * hw := 0b00 (no shift), 0b01 (lsl #16), 0b10 (lsl #32) + * opc := 0b11 (MOVK), 0b00 (MOVN), 0b10 (MOVZ) + * sf := 1 (64-bit variant) + */ + plt[i] = (struct plt_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) + }; + + if (rela->r_addend == 0) + sym->st_size = (u64)&plt[i]; + + return (u64)&plt[i]; +} + +#define cmp_3way(a,b) ((a) < (b) ? -1 : (a) > (b)) + +static int cmp_rela(const void *a, const void *b) +{ + const Elf64_Rela *x = a, *y = b; + int i; + + /* sort by type, symbol index and addend */ + i = cmp_3way(ELF64_R_TYPE(x->r_info), ELF64_R_TYPE(y->r_info)); + if (i == 0) + i = cmp_3way(ELF64_R_SYM(x->r_info), ELF64_R_SYM(y->r_info)); + if (i == 0) + i = cmp_3way(x->r_addend, y->r_addend); + return i; +} + +static bool duplicate_rel(const Elf64_Rela *rela, int num) +{ + /* + * Entries are sorted by type, symbol index and addend. That means + * that, if a duplicate entry exists, it must be in the preceding + * slot. + */ + return num > 0 && cmp_rela(rela + num, rela + num - 1) == 0; +} + +static unsigned int count_plts(Elf64_Sym *syms, Elf64_Rela *rela, int num) +{ + unsigned int ret = 0; + Elf64_Sym *s; + int i; + + for (i = 0; i < num; i++) { + switch (ELF64_R_TYPE(rela[i].r_info)) { + case R_AARCH64_JUMP26: + case R_AARCH64_CALL26: + /* + * We only have to consider branch targets that resolve + * to undefined symbols. This is not simply a heuristic, + * it is a fundamental limitation, since the PLT itself + * is part of the module, and needs to be within 128 MB + * as well, so modules can never grow beyond that limit. + */ + s = syms + ELF64_R_SYM(rela[i].r_info); + if (s->st_shndx != SHN_UNDEF) + break; + + /* + * Jump relocations with non-zero addends against + * undefined symbols are supported by the ELF spec, but + * do not occur in practice (e.g., 'jump n bytes past + * the entry point of undefined function symbol f'). + * So we need to support them, but there is no need to + * take them into consideration when trying to optimize + * this code. So let's only check for duplicates when + * the addend is zero: this allows us to record the PLT + * entry address in the symbol table itself, rather than + * having to search the list for duplicates each time we + * emit one. + */ + if (rela[i].r_addend != 0 || !duplicate_rel(rela, i)) + ret++; + break; + } + } + return ret; +} + +int module_frob_arch_sections(Elf_Ehdr *ehdr, Elf_Shdr *sechdrs, + char *secstrings, struct module *mod) +{ + unsigned long plt_max_entries = 0; + Elf64_Sym *syms = NULL; + int i; + + /* + * Find the empty .plt section so we can expand it to store the PLT + * entries. Record the symtab address as well. + */ + for (i = 0; i < ehdr->e_shnum; i++) { + if (strcmp(".plt", secstrings + sechdrs[i].sh_name) == 0) + mod->arch.plt = sechdrs + i; + else if (sechdrs[i].sh_type == SHT_SYMTAB) + syms = (Elf64_Sym *)sechdrs[i].sh_addr; + } + + if (!mod->arch.plt) { + pr_err("%s: module PLT section missing\n", mod->name); + return -ENOEXEC; + } + if (!syms) { + pr_err("%s: module symtab section missing\n", mod->name); + return -ENOEXEC; + } + + for (i = 0; i < ehdr->e_shnum; i++) { + Elf64_Rela *rels = (void *)ehdr + sechdrs[i].sh_offset; + int numrels = sechdrs[i].sh_size / sizeof(Elf64_Rela); + Elf64_Shdr *dstsec = sechdrs + sechdrs[i].sh_info; + + if (sechdrs[i].sh_type != SHT_RELA) + continue; + + /* ignore relocations that operate on non-exec sections */ + if (!(dstsec->sh_flags & SHF_EXECINSTR)) + continue; + + /* sort by type, symbol index and addend */ + sort(rels, numrels, sizeof(Elf64_Rela), cmp_rela, NULL); + + plt_max_entries += count_plts(syms, rels, numrels); + } + + mod->arch.plt->sh_type = SHT_NOBITS; + mod->arch.plt->sh_flags = SHF_EXECINSTR | SHF_ALLOC; + mod->arch.plt->sh_addralign = L1_CACHE_BYTES; + mod->arch.plt->sh_size = plt_max_entries * sizeof(struct plt_entry); + mod->arch.plt_num_entries = 0; + mod->arch.plt_max_entries = plt_max_entries; + return 0; +} diff --git a/arch/arm64/kernel/module.c b/arch/arm64/kernel/module.c index 93e9702..a9dde97 100644 --- a/arch/arm64/kernel/module.c +++ b/arch/arm64/kernel/module.c @@ -38,6 +38,21 @@ void *module_alloc(unsigned long size) GFP_KERNEL, PAGE_KERNEL_EXEC, 0, NUMA_NO_NODE, __builtin_return_address(0)); + if (!p && IS_ENABLED(CONFIG_ARM64_MODULE_PLTS) && + !IS_ENABLED(CONFIG_KASAN)) + /* + * KASAN can only deal with module allocations being served + * from the reserved module region, since the remainder of + * the vmalloc region is already backed by zero shadow pages, + * and punching holes into it is non-trivial. Since the module + * region is not randomized when KASAN is enabled, it is even + * less likely that the module region gets exhausted, so we + * can simply omit this fallback in that case. + */ + p = __vmalloc_node_range(size, MODULE_ALIGN, VMALLOC_START, + VMALLOC_END, GFP_KERNEL, PAGE_KERNEL_EXEC, 0, + NUMA_NO_NODE, __builtin_return_address(0)); + if (p && (kasan_module_alloc(p, size) < 0)) { vfree(p); return NULL; @@ -361,6 +376,13 @@ 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 = module_emit_plt_entry(me, &rel[i], sym); + 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 0000000..8949f6c --- /dev/null +++ b/arch/arm64/kernel/module.lds @@ -0,0 +1,3 @@ +SECTIONS { + .plt (NOLOAD) : { BYTE(0) } +} |
