Messages in this thread Patch in this message | | | Date | Thu, 24 Feb 2022 15:52:14 +0100 | From | Peter Zijlstra <> | Subject | [PATCH v2 36/39] objtool: Find unused ENDBR instructions |
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Find all unused ENDBR instructions and stick them in a section such that the kernel can poison them.
Signed-off-by: Peter Zijlstra (Intel) <peterz@infradead.org> --- arch/x86/kernel/vmlinux.lds.S | 9 ++++ tools/objtool/builtin-check.c | 3 - tools/objtool/check.c | 72 +++++++++++++++++++++++++++++++- tools/objtool/include/objtool/builtin.h | 2 tools/objtool/include/objtool/objtool.h | 1 tools/objtool/objtool.c | 1 6 files changed, 85 insertions(+), 3 deletions(-)
--- a/arch/x86/kernel/vmlinux.lds.S +++ b/arch/x86/kernel/vmlinux.lds.S @@ -285,6 +285,15 @@ SECTIONS } #endif +#ifdef CONFIG_X86_KERNEL_IBT + . = ALIGN(8); + .ibt_endbr_sites : AT(ADDR(.ibt_endbr_sites) - LOAD_OFFSET) { + __ibt_endbr_sites = .; + *(.ibt_endbr_sites) + __ibt_endbr_sites_end = .; + } +#endif + /* * struct alt_inst entries. From the header (alternative.h): * "Alternative instructions for different CPU types or capabilities" --- a/tools/objtool/builtin-check.c +++ b/tools/objtool/builtin-check.c @@ -21,7 +21,7 @@ bool no_fp, no_unreachable, retpoline, module, backtrace, uaccess, stats, lto, vmlinux, mcount, noinstr, backup, sls, dryrun, - ibt, ibt_fix_direct; + ibt, ibt_fix_direct, ibt_seal; static const char * const check_usage[] = { "objtool check [<options>] file.o", @@ -50,6 +50,7 @@ const struct option check_options[] = { OPT_BOOLEAN(0, "dry-run", &dryrun, "don't write the modifications"), OPT_BOOLEAN(0, "ibt", &ibt, "validate ENDBR placement"), OPT_BOOLEAN(0, "ibt-fix-direct", &ibt_fix_direct, "fixup direct jmp/call to ENDBR"), + OPT_BOOLEAN(0, "ibt-seal", &ibt_seal, "list superfluous ENDBR instructions"), OPT_END(), }; --- a/tools/objtool/check.c +++ b/tools/objtool/check.c @@ -732,6 +732,58 @@ static int create_retpoline_sites_sectio return 0; } +static int create_ibt_endbr_sites_sections(struct objtool_file *file) +{ + struct instruction *insn; + struct section *sec; + int idx; + + sec = find_section_by_name(file->elf, ".ibt_endbr_sites"); + if (sec) { + WARN("file already has .ibt_endbr_sites, skipping"); + return 0; + } + + idx = 0; + list_for_each_entry(insn, &file->endbr_list, call_node) + idx++; + + if (stats) { + printf("ibt: ENDBR at function start: %d\n", file->nr_endbr); + printf("ibt: ENDBR inside functions: %d\n", file->nr_endbr_int); + printf("ibt: superfluous ENDBR: %d\n", idx); + } + + if (!idx) + return 0; + + sec = elf_create_section(file->elf, ".ibt_endbr_sites", 0, + sizeof(int), idx); + if (!sec) { + WARN("elf_create_section: .ibt_endbr_sites"); + return -1; + } + + idx = 0; + list_for_each_entry(insn, &file->endbr_list, call_node) { + + int *site = (int *)sec->data->d_buf + idx; + *site = 0; + + if (elf_add_reloc_to_insn(file->elf, sec, + idx * sizeof(int), + R_X86_64_PC32, + insn->sec, insn->offset)) { + WARN("elf_add_reloc_to_insn: .ibt_endbr_sites"); + return -1; + } + + idx++; + } + + return 0; +} + static int create_mcount_loc_sections(struct objtool_file *file) { struct section *sec; @@ -1179,6 +1231,7 @@ static int add_jump_destinations(struct for_each_insn(file, insn) { if (insn->type == INSN_ENDBR && insn->func) { if (insn->offset == insn->func->offset) { + list_add_tail(&insn->call_node, &file->endbr_list); file->nr_endbr++; } else { file->nr_endbr_int++; @@ -3633,8 +3687,12 @@ validate_ibt_reloc(struct objtool_file * if (!dest) return NULL; - if (dest->type == INSN_ENDBR) + if (dest->type == INSN_ENDBR) { + if (!list_empty(&dest->call_node)) + list_del_init(&dest->call_node); + return NULL; + } if (reloc->sym->static_call_tramp) return NULL; @@ -3777,6 +3835,11 @@ int check(struct objtool_file *file) return 1; } + if (ibt_seal && !ibt_fix_direct) { + fprintf(stderr, "--ibt-seal requires: --ibt-fix-direct\n"); + return 1; + } + arch_initial_func_cfi_state(&initial_func_cfi); init_cfi_state(&init_cfi); init_cfi_state(&func_cfi); @@ -3854,6 +3917,13 @@ int check(struct objtool_file *file) if (ret < 0) goto out; warnings += ret; + } + + if (ibt_seal) { + ret = create_ibt_endbr_sites_sections(file); + if (ret < 0) + goto out; + warnings += ret; } if (stats) { --- a/tools/objtool/include/objtool/builtin.h +++ b/tools/objtool/include/objtool/builtin.h @@ -10,7 +10,7 @@ extern const struct option check_options[]; extern bool no_fp, no_unreachable, retpoline, module, backtrace, uaccess, stats, lto, vmlinux, mcount, noinstr, backup, sls, dryrun, - ibt, ibt_fix_direct; + ibt, ibt_fix_direct, ibt_seal; extern int cmd_parse_options(int argc, const char **argv, const char * const usage[]); --- a/tools/objtool/include/objtool/objtool.h +++ b/tools/objtool/include/objtool/objtool.h @@ -26,6 +26,7 @@ struct objtool_file { struct list_head retpoline_call_list; struct list_head static_call_list; struct list_head mcount_loc_list; + struct list_head endbr_list; bool ignore_unreachables, c_file, hints, rodata; unsigned int nr_endbr; --- a/tools/objtool/objtool.c +++ b/tools/objtool/objtool.c @@ -128,6 +128,7 @@ struct objtool_file *objtool_open_read(c INIT_LIST_HEAD(&file.retpoline_call_list); INIT_LIST_HEAD(&file.static_call_list); INIT_LIST_HEAD(&file.mcount_loc_list); + INIT_LIST_HEAD(&file.endbr_list); file.c_file = !vmlinux && find_section_by_name(file.elf, ".comment"); file.ignore_unreachables = no_unreachable; file.hints = false;
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