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authorPeter Zijlstra <peterz@infradead.org>2020-05-08 13:34:33 +0300
committerPeter Zijlstra <peterz@infradead.org>2020-05-15 11:35:12 +0300
commitab3852ab5cb8fd2e2c5bfa176e5f953353836907 (patch)
tree06b5772f99cd8e99d278db1f3ee8b328953b5658 /tools/objtool
parentcc1ac9c792810b93783a7de344f428922af8d98c (diff)
downloadlinux-ab3852ab5cb8fd2e2c5bfa176e5f953353836907.tar.xz
objtool: Allow no-op CFI ops in alternatives
Randy reported a false-positive: arch/x86/hyperv/hv_apic.o: warning: objtool: hv_apic_write()+0x25: alternative modifies stack What happens is that: alternative_io("movl %0, %P1", "xchgl %0, %P1", X86_BUG_11AP, 13d: 89 9d 00 d0 7f ff mov %ebx,-0x803000(%rbp) decodes to an instruction with CFI-ops because it modifies RBP. However, due to this being a !frame-pointer build, that should not in fact change the CFI state. So instead of dis-allowing any CFI-op, verify the op would've actually changed the CFI state. Fixes: 7117f16bf460 ("objtool: Fix ORC vs alternatives") Reported-by: Randy Dunlap <rdunlap@infradead.org> Signed-off-by: Peter Zijlstra (Intel) <peterz@infradead.org> Acked-by: Josh Poimboeuf <jpoimboe@redhat.com> Acked-by: Randy Dunlap <rdunlap@infradead.org> Tested-by: Randy Dunlap <rdunlap@infradead.org>
Diffstat (limited to 'tools/objtool')
-rw-r--r--tools/objtool/check.c11
1 files changed, 6 insertions, 5 deletions
diff --git a/tools/objtool/check.c b/tools/objtool/check.c
index 32dea5f3feed..196a55101f3c 100644
--- a/tools/objtool/check.c
+++ b/tools/objtool/check.c
@@ -2060,17 +2060,18 @@ static int handle_insn_ops(struct instruction *insn, struct insn_state *state)
struct stack_op *op;
list_for_each_entry(op, &insn->stack_ops, list) {
+ struct cfi_state old_cfi = state->cfi;
int res;
- if (insn->alt_group) {
- WARN_FUNC("alternative modifies stack", insn->sec, insn->offset);
- return -1;
- }
-
res = update_cfi_state(insn, &state->cfi, op);
if (res)
return res;
+ if (insn->alt_group && memcmp(&state->cfi, &old_cfi, sizeof(struct cfi_state))) {
+ WARN_FUNC("alternative modifies stack", insn->sec, insn->offset);
+ return -1;
+ }
+
if (op->dest.type == OP_DEST_PUSHF) {
if (!state->uaccess_stack) {
state->uaccess_stack = 1;