The following commit has been merged into the objtool/core branch of tip:
Commit-ID: ab3852ab5cb8fd2e2c5bfa176e5f953353836907
Gitweb: https://git.kernel.org/tip/ab3852ab5cb8fd2e2c5bfa176e5f953353836907
Author: Peter Zijlstra <peterz@xxxxxxxxxxxxx>
AuthorDate: Fri, 08 May 2020 12:34:33 +02:00
Committer: Peter Zijlstra <peterz@xxxxxxxxxxxxx>
CommitterDate: Fri, 15 May 2020 10:35:12 +02:00
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@xxxxxxxxxxxxx>
Signed-off-by: Peter Zijlstra (Intel) <peterz@xxxxxxxxxxxxx>
Acked-by: Josh Poimboeuf <jpoimboe@xxxxxxxxxx>
Acked-by: Randy Dunlap <rdunlap@xxxxxxxxxxxxx>
Tested-by: Randy Dunlap <rdunlap@xxxxxxxxxxxxx>
---
tools/objtool/check.c | 11 ++++++-----
1 file changed, 6 insertions(+), 5 deletions(-)
diff --git a/tools/objtool/check.c b/tools/objtool/check.c
index 32dea5f..196a551 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;
|