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SubjectRe: [PATCH v2] arm64/module: use mod->klp_info section header information for livepatch modules

> >Does this mean we can drop the plt pointer from this struct altogether, and
> >simply offset into the section headers when applying the relocations?
>
> Hmm, if everyone is OK with dropping the plt pointer from struct
> mod_plt_sec, then I think we can simplify this patch even further.
>
> With the plt shndx saved, we can additionally pass a pointer to
> sechdrs to module_emit_plt_entry(), and with that just offset into the
> section headers as you suggest. Since livepatch *already* passes in
> the correct copy of the section headers (mod->klp_info->sechdrs) to
> apply_relocate_add(), we wouldn't even need to modify the arm64
> module_finalize() to change mod->arch.core.plt to point into
> mod->klp_info->sechdrs anymore and we can drop all the changes to the
> module loader too.
>
> Something like the following maybe?
>
> diff --git a/arch/arm64/include/asm/module.h b/arch/arm64/include/asm/module.h
> index fef773c94e9d..ac10fa066487 100644
> --- 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;
> };
> @@ -37,10 +37,12 @@ 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 f0690c2ca3e0..3cd744a1cbc2 100644
> --- a/arch/arm64/kernel/module-plts.c
> +++ b/arch/arm64/kernel/module-plts.c
> @@ -16,13 +16,15 @@ 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;
> - int i = pltsec->plt_num_entries;
> + struct mod_plt_sec *plt_info = !in_init(mod, loc) ? &mod->arch.core :
> + &mod->arch.init;
> + Elf64_Shdr *pltsec = sechdrs + plt_info->plt_shndx;
> + struct plt_entry *plt = (struct plt_entry *)pltsec->sh_addr;
> + int i = plt_info->plt_num_entries;
> u64 val = sym->st_value + rela->r_addend;
>
> plt[i] = get_plt_entry(val);
> @@ -35,24 +37,26 @@ u64 module_emit_plt_entry(struct module *mod, void *loc,
> const Elf64_Rela *rela,
> if (i > 0 && plt_entries_equal(plt + i, plt + i - 1))
> return (u64)&plt[i - 1];
>
> - pltsec->plt_num_entries++;
> - if (WARN_ON(pltsec->plt_num_entries > pltsec->plt_max_entries))
> + plt_info->plt_num_entries++;
> + if (WARN_ON(plt_info->plt_num_entries > plt_info->plt_max_entries))
> return 0;
>
> return (u64)&plt[i];
> }
>
> #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;
> - int i = pltsec->plt_num_entries++;
> + struct mod_plt_sec *plt_info = !in_init(mod, loc) ? &mod->arch.core :
> + &mod->arch.init;
> + Elf64_Shdr *pltsec = sechdrs + plt_info->plt_shndx;
> + struct plt_entry *plt = (struct plt_entry *)pltsec->sh_addr;
> + int i = plt_info->plt_num_entries++;
> u32 mov0, mov1, mov2, br;
> int rd;
>
> - if (WARN_ON(pltsec->plt_num_entries > pltsec->plt_max_entries))
> + if (WARN_ON(plt_info->plt_num_entries > plt_info->plt_max_entries))
> return 0;
>
> /* get the destination register of the ADRP instruction */
> @@ -202,7 +206,7 @@ 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 +215,9 @@ 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 +226,7 @@ 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 +258,19 @@ 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 dd23655fda3a..8e6444db2d8e 100644
> --- 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,
>
> Perhaps this approach is better. Miroslav and Petr, do you think this
> would work? (Apologies for the efforts to review the last two
> versions, if we end up scrapping the old patch :-/)

No problem. I think it should work and it looks good to me (I did not
compile it though). I'm glad we don't have to touch load_module(). The
function is complicated enough.

Thanks,
Miroslav

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