On 5/8/20 3:38 AM, Peter Zijlstra wrote: > On Tue, May 05, 2020 at 10:40:43PM -0700, Randy Dunlap wrote: >> On 5/5/20 3:29 PM, akpm@xxxxxxxxxxxxxxxxxxxx wrote: >>> The mm-of-the-moment snapshot 2020-05-05-15-28 has been uploaded to >>> >>> http://www.ozlabs.org/~akpm/mmotm/ >>> >>> mmotm-readme.txt says >>> >>> README for mm-of-the-moment: >>> >>> http://www.ozlabs.org/~akpm/mmotm/ >>> >>> This is a snapshot of my -mm patch queue. Uploaded at random hopefully >>> more than once a week. >>> >> >> >> on x86_64: >> >> arch/x86/hyperv/hv_apic.o: warning: objtool: hv_apic_write()+0x25: alternative modifies stack > > Wheee... this seems to have cured it for me. > > --- > Subject: objtool: Allow no-op CFI ops in alternatives > From: Peter Zijlstra <peterz@xxxxxxxxxxxxx> > Date: Fri May 8 12:34:33 CEST 2020 > > Randy reported a false-positive: "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: Randy Dunlap <rdunlap@xxxxxxxxxxxxx> Tested-by: Randy Dunlap <rdunlap@xxxxxxxxxxxxx> Thanks. > --- > tools/objtool/check.c | 11 ++++++----- > 1 file changed, 6 insertions(+), 5 deletions(-) > > --- a/tools/objtool/check.c > +++ b/tools/objtool/check.c > @@ -2078,17 +2078,18 @@ static int handle_insn_ops(struct instru > 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; > -- ~Randy
