For all CONFIG_CFI+CONFIG_CALL_PADDING configs, for C functions, the __cfi_ symbols only cover the 5-byte kCFI type hash. After that there also N bytes of NOP padding between the hash and the function entry which aren't associated with any symbol.
The NOPs can be replaced with actual code at runtime. Without a symbol, unwinders and tooling have no way of knowing where those bytes belong. Grow the existing __cfi_* symbols to fill that gap. Note that assembly functions with SYM_TYPED_FUNC_START() aren't affected by this issue, their __cfi_ symbols also cover the padding. Also, CONFIG_PREFIX_SYMBOLS has no reason to exist: CONFIG_CALL_PADDING is what causes the compiler to emit NOP padding before function entry (via -fpatchable-function-entry), so it's the right condition for creating prefix symbols. Remove CONFIG_PREFIX_SYMBOLS, as it's no longer needed. Simplify the LONGEST_SYM_KUNIT_TEST dependency accordingly. Rework objtool's arguments a bit to handle the variety of prefix/cfi-related cases. Suggested-by: Peter Zijlstra <[email protected]> Signed-off-by: Josh Poimboeuf <[email protected]> --- arch/x86/Kconfig | 4 -- lib/Kconfig.debug | 2 +- scripts/Makefile.lib | 7 +++- tools/objtool/builtin-check.c | 15 +++++++- tools/objtool/check.c | 49 ++++++++++++++++++++----- tools/objtool/elf.c | 20 ++++++++++ tools/objtool/include/objtool/builtin.h | 7 ++-- tools/objtool/include/objtool/elf.h | 1 + 8 files changed, 84 insertions(+), 21 deletions(-) diff --git a/arch/x86/Kconfig b/arch/x86/Kconfig index f3f7cb01d69d..3eb3c48d764a 100644 --- a/arch/x86/Kconfig +++ b/arch/x86/Kconfig @@ -2437,10 +2437,6 @@ config CALL_THUNKS def_bool n select CALL_PADDING -config PREFIX_SYMBOLS - def_bool y - depends on CALL_PADDING && !CFI - menuconfig CPU_MITIGATIONS bool "Mitigations for CPU vulnerabilities" default y diff --git a/lib/Kconfig.debug b/lib/Kconfig.debug index 8ff5adcfe1e0..4f7496b3268d 100644 --- a/lib/Kconfig.debug +++ b/lib/Kconfig.debug @@ -3070,7 +3070,7 @@ config FORTIFY_KUNIT_TEST config LONGEST_SYM_KUNIT_TEST tristate "Test the longest symbol possible" if !KUNIT_ALL_TESTS depends on KUNIT && KPROBES - depends on !PREFIX_SYMBOLS && !CFI && !GCOV_KERNEL + depends on !CALL_PADDING && !CFI && !GCOV_KERNEL default KUNIT_ALL_TESTS help Tests the longest symbol possible diff --git a/scripts/Makefile.lib b/scripts/Makefile.lib index 0718e39cedda..7e216d82e988 100644 --- a/scripts/Makefile.lib +++ b/scripts/Makefile.lib @@ -187,7 +187,11 @@ objtool-args-$(CONFIG_HAVE_JUMP_LABEL_HACK) += --hacks=jump_label objtool-args-$(CONFIG_HAVE_NOINSTR_HACK) += --hacks=noinstr objtool-args-$(CONFIG_MITIGATION_CALL_DEPTH_TRACKING) += --hacks=skylake objtool-args-$(CONFIG_X86_KERNEL_IBT) += --ibt -objtool-args-$(CONFIG_FINEIBT) += --cfi +objtool-args-$(CONFIG_CALL_PADDING) += --prefix=$(CONFIG_FUNCTION_PADDING_BYTES) +ifdef CONFIG_CALL_PADDING +objtool-args-$(CONFIG_CFI) += --cfi +objtool-args-$(CONFIG_FINEIBT) += --fineibt +endif objtool-args-$(CONFIG_FTRACE_MCOUNT_USE_OBJTOOL) += --mcount ifdef CONFIG_FTRACE_MCOUNT_USE_OBJTOOL objtool-args-$(CONFIG_HAVE_OBJTOOL_NOP_MCOUNT) += --mnop @@ -200,7 +204,6 @@ objtool-args-$(CONFIG_STACK_VALIDATION) += --stackval objtool-args-$(CONFIG_HAVE_STATIC_CALL_INLINE) += --static-call objtool-args-$(CONFIG_HAVE_UACCESS_VALIDATION) += --uaccess objtool-args-$(or $(CONFIG_GCOV_KERNEL),$(CONFIG_KCOV)) += --no-unreachable -objtool-args-$(CONFIG_PREFIX_SYMBOLS) += --prefix=$(CONFIG_FUNCTION_PADDING_BYTES) objtool-args-$(CONFIG_OBJTOOL_WERROR) += --werror objtool-args = $(objtool-args-y) \ diff --git a/tools/objtool/builtin-check.c b/tools/objtool/builtin-check.c index ec7f10a5ef19..118c3de2f293 100644 --- a/tools/objtool/builtin-check.c +++ b/tools/objtool/builtin-check.c @@ -73,7 +73,6 @@ static int parse_hacks(const struct option *opt, const char *str, int unset) static const struct option check_options[] = { OPT_GROUP("Actions:"), - OPT_BOOLEAN(0, "cfi", &opts.cfi, "annotate kernel control flow integrity (kCFI) function preambles"), OPT_STRING_OPTARG('d', "disas", &opts.disas, "function-pattern", "disassemble functions", "*"), OPT_CALLBACK_OPTARG('h', "hacks", NULL, NULL, "jump_label,noinstr,skylake", "patch toolchain bugs/limitations", parse_hacks), OPT_BOOLEAN('i', "ibt", &opts.ibt, "validate and annotate IBT"), @@ -84,7 +83,7 @@ static const struct option check_options[] = { OPT_BOOLEAN('r', "retpoline", &opts.retpoline, "validate and annotate retpoline usage"), OPT_BOOLEAN(0, "rethunk", &opts.rethunk, "validate and annotate rethunk usage"), OPT_BOOLEAN(0, "unret", &opts.unret, "validate entry unret placement"), - OPT_INTEGER(0, "prefix", &opts.prefix, "generate prefix symbols"), + OPT_INTEGER(0, "prefix", &opts.prefix, "generate or grow prefix symbols for N-byte function padding"), OPT_BOOLEAN('l', "sls", &opts.sls, "validate straight-line-speculation mitigations"), OPT_BOOLEAN('s', "stackval", &opts.stackval, "validate frame pointer rules"), OPT_BOOLEAN('t', "static-call", &opts.static_call, "annotate static calls"), @@ -92,6 +91,8 @@ static const struct option check_options[] = { OPT_CALLBACK_OPTARG(0, "dump", NULL, NULL, "orc", "dump metadata", parse_dump), OPT_GROUP("Options:"), + OPT_BOOLEAN(0, "cfi", &opts.cfi, "grow kCFI preamble symbols (use with --prefix)"), + OPT_BOOLEAN(0, "fineibt", &opts.fineibt, "create .cfi_sites section for FineIBT"), OPT_BOOLEAN(0, "backtrace", &opts.backtrace, "unwind on error"), OPT_BOOLEAN(0, "backup", &opts.backup, "create backup (.orig) file on warning/error"), OPT_BOOLEAN(0, "dry-run", &opts.dryrun, "don't write modifications"), @@ -163,6 +164,16 @@ static bool opts_valid(void) return false; } + if (opts.cfi && !opts.prefix) { + ERROR("--cfi requires --prefix"); + return false; + } + + if (opts.fineibt && !opts.cfi) { + ERROR("--fineibt requires --cfi"); + return false; + } + if (opts.disas || opts.hack_jump_label || opts.hack_noinstr || diff --git a/tools/objtool/check.c b/tools/objtool/check.c index 410061aeed26..0d9b859b006e 100644 --- a/tools/objtool/check.c +++ b/tools/objtool/check.c @@ -881,6 +881,31 @@ static int create_ibt_endbr_seal_sections(struct objtool_file *file) return 0; } +/* +* Grow __cfi_ symbols to fill the NOP gap between the 'mov <hash>, %rax' and +* the start of the function. +*/ +static int grow_cfi_symbols(struct objtool_file *file) +{ + struct symbol *sym; + + for_each_sym(file->elf, sym) { + if (!is_func_sym(sym) || !strstarts(sym->name, "__cfi_") || + sym->len != 5) + continue; + + if (!find_func_by_offset(sym->sec, sym->offset + sym->len + opts.prefix)) + continue; + + sym->len += opts.prefix; + sym->sym.st_size = sym->len; + if (elf_write_symbol(file->elf, sym)) + return -1; + } + + return 0; +} + static int create_cfi_sections(struct objtool_file *file) { struct section *sec; @@ -4903,12 +4928,6 @@ int check(struct objtool_file *file) goto out; } - if (opts.cfi) { - ret = create_cfi_sections(file); - if (ret) - goto out; - } - if (opts.rethunk) { ret = create_return_sites_sections(file); if (ret) @@ -4928,9 +4947,21 @@ int check(struct objtool_file *file) } if (opts.prefix) { - ret = create_prefix_symbols(file); - if (ret) - goto out; + if (!opts.cfi) { + ret = create_prefix_symbols(file); + if (ret) + goto out; + } else { + ret = grow_cfi_symbols(file); + if (ret) + goto out; + + if (opts.fineibt) { + ret = create_cfi_sections(file); + if (ret) + goto out; + } + } } if (opts.ibt) { diff --git a/tools/objtool/elf.c b/tools/objtool/elf.c index d9cee8d5d9e8..33c95a74a51b 100644 --- a/tools/objtool/elf.c +++ b/tools/objtool/elf.c @@ -997,6 +997,26 @@ struct symbol *elf_create_symbol(struct elf *elf, const char *name, return sym; } +int elf_write_symbol(struct elf *elf, struct symbol *sym) +{ + struct section *symtab, *symtab_shndx; + + symtab = find_section_by_name(elf, ".symtab"); + if (!symtab) { + ERROR("no .symtab"); + return -1; + } + + symtab_shndx = find_section_by_name(elf, ".symtab_shndx"); + + if (elf_update_symbol(elf, symtab, symtab_shndx, sym)) + return -1; + + mark_sec_changed(elf, symtab, true); + + return 0; +} + struct symbol *elf_create_section_symbol(struct elf *elf, struct section *sec) { struct symbol *sym = calloc(1, sizeof(*sym)); diff --git a/tools/objtool/include/objtool/builtin.h b/tools/objtool/include/objtool/builtin.h index b9e229ed4dc0..e844e9c82b7b 100644 --- a/tools/objtool/include/objtool/builtin.h +++ b/tools/objtool/include/objtool/builtin.h @@ -9,8 +9,8 @@ struct opts { /* actions: */ - bool cfi; bool checksum; + const char *disas; bool dump_orc; bool hack_jump_label; bool hack_noinstr; @@ -20,6 +20,7 @@ struct opts { bool noabs; bool noinstr; bool orc; + int prefix; bool retpoline; bool rethunk; bool unret; @@ -27,14 +28,14 @@ struct opts { bool stackval; bool static_call; bool uaccess; - int prefix; - const char *disas; /* options: */ bool backtrace; bool backup; + bool cfi; const char *debug_checksum; bool dryrun; + bool fineibt; bool link; bool mnop; bool module; diff --git a/tools/objtool/include/objtool/elf.h b/tools/objtool/include/objtool/elf.h index e452784df702..305183f30a33 100644 --- a/tools/objtool/include/objtool/elf.h +++ b/tools/objtool/include/objtool/elf.h @@ -199,6 +199,7 @@ struct reloc *elf_init_reloc_data_sym(struct elf *elf, struct section *sec, struct symbol *sym, s64 addend); +int elf_write_symbol(struct elf *elf, struct symbol *sym); int elf_write_insn(struct elf *elf, struct section *sec, unsigned long offset, unsigned int len, const char *insn); -- 2.53.0
