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: Ard Biesheuvel <ard.biesheuvel@linaro.org>
Reviewed-by: Miroslav Benes <mbenes@suse.cz>
Signed-off-by: Jessica Yu <jeyu@kernel.org>
Signed-off-by: Will Deacon <will.deacon@arm.com>

diff --git a/arch/arm64/include/asm/module.h b/arch/arm64/include/asm/module.h
index 97d0ef12e2ff561938acdf96196a1a213664c522..f81c1847312dba9a9e2f27ed6c7c3b209abc5328 100644 (file)
--- a/arch/arm64/include/asm/module.h
+++ b/arch/arm64/include/asm/module.h
@@ -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;

diff --git a/arch/arm64/kernel/module-plts.c b/arch/arm64/kernel/module-plts.c
index f0690c2ca3e0f2f27f761a1568e6b3cc637779a4..a0efe30211d66b0fa8e419a35458f37ca5067707 100644 (file)
--- a/arch/arm64/kernel/module-plts.c
+++ b/arch/arm64/kernel/module-plts.c
@@ -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;
 

diff --git a/arch/arm64/kernel/module.c b/arch/arm64/kernel/module.c
index f0f27aeefb73623a0983c1f3eec2054d306021dc..c2abe59c6f8f79d5e0e343f042b4c03c48154a8f 100644 (file)
--- a/arch/arm64/kernel/module.c
+++ b/arch/arm64/kernel/module.c
@@ -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,