From ab3852ab5cb8fd2e2c5bfa176e5f953353836907 Mon Sep 17 00:00:00 2001 From: Peter Zijlstra Date: Fri, 8 May 2020 12:34:33 +0200 Subject: 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 Signed-off-by: Peter Zijlstra (Intel) Acked-by: Josh Poimboeuf Acked-by: Randy Dunlap Tested-by: Randy Dunlap --- tools/objtool/check.c | 11 ++++++----- 1 file changed, 6 insertions(+), 5 deletions(-) (limited to 'tools/objtool') 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; -- cgit v1.2.3