Commit c8ebf64e authored by Jessica Yu's avatar Jessica Yu Committed by Will Deacon
Browse files

arm64/module: use plt section indices for relocations 



Instead of saving a pointer to the .plt and .init.plt sections to apply
plt-based relocations, save and use their section indices instead.

The mod->arch.{core,init}.plt pointers were problematic for livepatch
because they pointed within temporary section headers (provided by the
module loader via info->sechdrs) that would be freed after module load.
Since livepatch modules may need to apply relocations post-module-load
(for example, to patch a module that is loaded later), using section
indices to offset into the section headers (instead of accessing them
through a saved pointer) allows livepatch modules on arm64 to pass in
their own copy of the section headers to apply_relocate_add() to apply
delayed relocations.

Reviewed-by: default avatarArd Biesheuvel <ard.biesheuvel@linaro.org>
Reviewed-by: default avatarMiroslav Benes <mbenes@suse.cz>
Signed-off-by: default avatarJessica Yu <jeyu@kernel.org>
Signed-off-by: default avatarWill Deacon <will.deacon@arm.com>
parent c55191e9

arch/arm64/include/asm/module.h

+5 −3
Original line number Diff line number Diff line
@@ -22,7 +22,7 @@ 


#ifdef CONFIG_ARM64_MODULE_PLTS

struct mod_plt_sec {

	struct elf64_shdr	*plt;

	int			plt_shndx;

	int			plt_num_entries;

	int			plt_max_entries;

};
@@ -36,10 +36,12 @@ struct mod_arch_specific { 
};

#endif



u64 module_emit_plt_entry(struct module *mod, void *loc, const Elf64_Rela *rela,

u64 module_emit_plt_entry(struct module *mod, Elf64_Shdr *sechdrs,

			  void *loc, const Elf64_Rela *rela,

			  Elf64_Sym *sym);



u64 module_emit_veneer_for_adrp(struct module *mod, void *loc, u64 val);

u64 module_emit_veneer_for_adrp(struct module *mod, Elf64_Shdr *sechdrs,

				void *loc, u64 val);



#ifdef CONFIG_RANDOMIZE_BASE

extern u64 module_alloc_base;

arch/arm64/kernel/module-plts.c

+20 −16
Original line number Diff line number Diff line
@@ -16,12 +16,13 @@ static bool in_init(const struct module *mod, void *loc) 
	return (u64)loc - (u64)mod->init_layout.base < mod->init_layout.size;

}



u64 module_emit_plt_entry(struct module *mod, void *loc, const Elf64_Rela *rela,

u64 module_emit_plt_entry(struct module *mod, Elf64_Shdr *sechdrs,

			  void *loc, const Elf64_Rela *rela,

			  Elf64_Sym *sym)

{

	struct mod_plt_sec *pltsec = !in_init(mod, loc) ? &mod->arch.core :

							  &mod->arch.init;

	struct plt_entry *plt = (struct plt_entry *)pltsec->plt->sh_addr;

	struct plt_entry *plt = (struct plt_entry *)sechdrs[pltsec->plt_shndx].sh_addr;

	int i = pltsec->plt_num_entries;

	u64 val = sym->st_value + rela->r_addend;
@@ -43,11 +44,12 @@ u64 module_emit_plt_entry(struct module *mod, void *loc, const Elf64_Rela *rela, 
}



#ifdef CONFIG_ARM64_ERRATUM_843419

u64 module_emit_veneer_for_adrp(struct module *mod, void *loc, u64 val)

u64 module_emit_veneer_for_adrp(struct module *mod, Elf64_Shdr *sechdrs,

				void *loc, u64 val)

{

	struct mod_plt_sec *pltsec = !in_init(mod, loc) ? &mod->arch.core :

							  &mod->arch.init;

	struct plt_entry *plt = (struct plt_entry *)pltsec->plt->sh_addr;

	struct plt_entry *plt = (struct plt_entry *)sechdrs[pltsec->plt_shndx].sh_addr;

	int i = pltsec->plt_num_entries++;

	u32 mov0, mov1, mov2, br;

	int rd;
@@ -202,7 +204,7 @@ int module_frob_arch_sections(Elf_Ehdr *ehdr, Elf_Shdr *sechdrs, 
	unsigned long core_plts = 0;

	unsigned long init_plts = 0;

	Elf64_Sym *syms = NULL;

	Elf_Shdr *tramp = NULL;

	Elf_Shdr *pltsec, *tramp = NULL;

	int i;



	/*
@@ -211,9 +213,9 @@ int module_frob_arch_sections(Elf_Ehdr *ehdr, Elf_Shdr *sechdrs, 
	 */

	for (i = 0; i < ehdr->e_shnum; i++) {

		if (!strcmp(secstrings + sechdrs[i].sh_name, ".plt"))

			mod->arch.core.plt = sechdrs + i;

			mod->arch.core.plt_shndx = i;

		else if (!strcmp(secstrings + sechdrs[i].sh_name, ".init.plt"))

			mod->arch.init.plt = sechdrs + i;

			mod->arch.init.plt_shndx = i;

		else if (IS_ENABLED(CONFIG_DYNAMIC_FTRACE) &&

			 !strcmp(secstrings + sechdrs[i].sh_name,

				 ".text.ftrace_trampoline"))
@@ -222,7 +224,7 @@ int module_frob_arch_sections(Elf_Ehdr *ehdr, Elf_Shdr *sechdrs, 
			syms = (Elf64_Sym *)sechdrs[i].sh_addr;

	}



	if (!mod->arch.core.plt || !mod->arch.init.plt) {

	if (!mod->arch.core.plt_shndx || !mod->arch.init.plt_shndx) {

		pr_err("%s: module PLT section(s) missing\n", mod->name);

		return -ENOEXEC;

	}
@@ -254,17 +256,19 @@ int module_frob_arch_sections(Elf_Ehdr *ehdr, Elf_Shdr *sechdrs, 
						sechdrs[i].sh_info, dstsec);

	}



	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  + 1) * sizeof(struct plt_entry);

	pltsec = sechdrs + mod->arch.core.plt_shndx;

	pltsec->sh_type = SHT_NOBITS;

	pltsec->sh_flags = SHF_EXECINSTR | SHF_ALLOC;

	pltsec->sh_addralign = L1_CACHE_BYTES;

	pltsec->sh_size = (core_plts  + 1) * sizeof(struct plt_entry);

	mod->arch.core.plt_num_entries = 0;

	mod->arch.core.plt_max_entries = core_plts;



	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 + 1) * sizeof(struct plt_entry);

	pltsec = sechdrs + mod->arch.init.plt_shndx;

	pltsec->sh_type = SHT_NOBITS;

	pltsec->sh_flags = SHF_EXECINSTR | SHF_ALLOC;

	pltsec->sh_addralign = L1_CACHE_BYTES;

	pltsec->sh_size = (init_plts + 1) * sizeof(struct plt_entry);

	mod->arch.init.plt_num_entries = 0;

	mod->arch.init.plt_max_entries = init_plts;

arch/arm64/kernel/module.c

+5 −4
Original line number Diff line number Diff line
@@ -198,7 +198,8 @@ static int reloc_insn_imm(enum aarch64_reloc_op op, __le32 *place, u64 val, 
	return 0;

}



static int reloc_insn_adrp(struct module *mod, __le32 *place, u64 val)

static int reloc_insn_adrp(struct module *mod, Elf64_Shdr *sechdrs,

			   __le32 *place, u64 val)

{

	u32 insn;
@@ -215,7 +216,7 @@ static int reloc_insn_adrp(struct module *mod, __le32 *place, u64 val) 
		insn &= ~BIT(31);

	} else {

		/* out of range for ADR -> emit a veneer */

		val = module_emit_veneer_for_adrp(mod, place, val & ~0xfff);

		val = module_emit_veneer_for_adrp(mod, sechdrs, place, val & ~0xfff);

		if (!val)

			return -ENOEXEC;

		insn = aarch64_insn_gen_branch_imm((u64)place, val,
@@ -368,7 +369,7 @@ int apply_relocate_add(Elf64_Shdr *sechdrs, 
		case R_AARCH64_ADR_PREL_PG_HI21_NC:

			overflow_check = false;

		case R_AARCH64_ADR_PREL_PG_HI21:

			ovf = reloc_insn_adrp(me, loc, val);

			ovf = reloc_insn_adrp(me, sechdrs, loc, val);

			if (ovf && ovf != -ERANGE)

				return ovf;

			break;
@@ -413,7 +414,7 @@ int apply_relocate_add(Elf64_Shdr *sechdrs, 


			if (IS_ENABLED(CONFIG_ARM64_MODULE_PLTS) &&

			    ovf == -ERANGE) {

				val = module_emit_plt_entry(me, loc, &rel[i], sym);

				val = module_emit_plt_entry(me, sechdrs, loc, &rel[i], sym);

				if (!val)

					return -ENOEXEC;

				ovf = reloc_insn_imm(RELOC_OP_PREL, loc, val, 2,

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