diff options
| author | Peter Zijlstra <peterz@infradead.org> | 2025-04-12 13:56:01 +0200 |
|---|---|---|
| committer | Peter Zijlstra <peterz@infradead.org> | 2025-08-18 14:23:09 +0200 |
| commit | 894af4a1cde61c3401f237184fb770f72ff12df8 (patch) | |
| tree | 6b00452a8bbc9e38b6d4578cf5990c19911724a0 /tools | |
| parent | 28d11e4548b75d0960429344f12d5f6cc9cee25b (diff) | |
objtool: Validate kCFI calls
Validate that all indirect calls adhere to kCFI rules. Notably doing
nocfi indirect call to a cfi function is broken.
Apparently some Rust 'core' code violates this and explodes when ran
with FineIBT.
All the ANNOTATE_NOCFI_SYM sites are prime targets for attackers.
- runtime EFI is especially henous because it also needs to disable
IBT. Basically calling unknown code without CFI protection at
runtime is a massice security issue.
- Kexec image handover; if you can exploit this, you get to keep it :-)
Signed-off-by: Peter Zijlstra (Intel) <peterz@infradead.org>
Acked-by: Josh Poimboeuf <jpoimboe@kernel.org>
Acked-by: Sean Christopherson <seanjc@google.com>
Link: https://lkml.kernel.org/r/20250714103441.496787279@infradead.org
Diffstat (limited to 'tools')
| -rw-r--r-- | tools/include/linux/objtool_types.h | 1 | ||||
| -rw-r--r-- | tools/objtool/check.c | 42 | ||||
| -rw-r--r-- | tools/objtool/include/objtool/elf.h | 1 |
3 files changed, 44 insertions, 0 deletions
diff --git a/tools/include/linux/objtool_types.h b/tools/include/linux/objtool_types.h index df5d9fa84dba..aceac94632c8 100644 --- a/tools/include/linux/objtool_types.h +++ b/tools/include/linux/objtool_types.h @@ -65,5 +65,6 @@ struct unwind_hint { #define ANNOTYPE_IGNORE_ALTS 6 #define ANNOTYPE_INTRA_FUNCTION_CALL 7 #define ANNOTYPE_REACHABLE 8 +#define ANNOTYPE_NOCFI 9 #endif /* _LINUX_OBJTOOL_TYPES_H */ diff --git a/tools/objtool/check.c b/tools/objtool/check.c index d14f20ef1db1..79eab61cd944 100644 --- a/tools/objtool/check.c +++ b/tools/objtool/check.c @@ -2392,6 +2392,8 @@ static int __annotate_ifc(struct objtool_file *file, int type, struct instructio static int __annotate_late(struct objtool_file *file, int type, struct instruction *insn) { + struct symbol *sym; + switch (type) { case ANNOTYPE_NOENDBR: /* early */ @@ -2433,6 +2435,15 @@ static int __annotate_late(struct objtool_file *file, int type, struct instructi insn->dead_end = false; break; + case ANNOTYPE_NOCFI: + sym = insn->sym; + if (!sym) { + ERROR_INSN(insn, "dodgy NOCFI annotation"); + return -1; + } + insn->sym->nocfi = 1; + break; + default: ERROR_INSN(insn, "Unknown annotation type: %d", type); return -1; @@ -4002,6 +4013,37 @@ static int validate_retpoline(struct objtool_file *file) warnings++; } + if (!opts.cfi) + return warnings; + + /* + * kCFI call sites look like: + * + * movl $(-0x12345678), %r10d + * addl -4(%r11), %r10d + * jz 1f + * ud2 + * 1: cs call __x86_indirect_thunk_r11 + * + * Verify all indirect calls are kCFI adorned by checking for the + * UD2. Notably, doing __nocfi calls to regular (cfi) functions is + * broken. + */ + list_for_each_entry(insn, &file->retpoline_call_list, call_node) { + struct symbol *sym = insn->sym; + + if (sym && (sym->type == STT_NOTYPE || + sym->type == STT_FUNC) && !sym->nocfi) { + struct instruction *prev = + prev_insn_same_sym(file, insn); + + if (!prev || prev->type != INSN_BUG) { + WARN_INSN(insn, "no-cfi indirect call!"); + warnings++; + } + } + } + return warnings; } diff --git a/tools/objtool/include/objtool/elf.h b/tools/objtool/include/objtool/elf.h index 0a2fa3ac0079..df8434d3b744 100644 --- a/tools/objtool/include/objtool/elf.h +++ b/tools/objtool/include/objtool/elf.h @@ -70,6 +70,7 @@ struct symbol { u8 local_label : 1; u8 frame_pointer : 1; u8 ignore : 1; + u8 nocfi : 1; struct list_head pv_target; struct reloc *relocs; struct section *group_sec; |