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| author | Peter Zijlstra <peterz@infradead.org> | 2020-05-08 12:34:33 +0200 |
|---|---|---|
| committer | Peter Zijlstra <peterz@infradead.org> | 2020-05-15 10:35:12 +0200 |
| commit | ab3852ab5cb8fd2e2c5bfa176e5f953353836907 (patch) | |
| tree | 06b5772f99cd8e99d278db1f3ee8b328953b5658 /tools/objtool | |
| parent | cc1ac9c792810b93783a7de344f428922af8d98c (diff) | |
| download | lwn-ab3852ab5cb8fd2e2c5bfa176e5f953353836907.tar.gz lwn-ab3852ab5cb8fd2e2c5bfa176e5f953353836907.zip | |
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.c | 11 |
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; |