Messages in this thread | | | Date | Tue, 28 Apr 2020 14:55:24 -0500 | From | Josh Poimboeuf <> | Subject | Re: [PATCH v2 02/14] objtool: Fix ORC vs alternatives |
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On Tue, Apr 28, 2020 at 09:11:03PM +0200, Peter Zijlstra wrote: > Jann reported that (for instance) entry_64.o:general_protection has > very odd ORC data: > > 0000000000000f40 <general_protection>: > #######sp:sp+8 bp:(und) type:iret end:0 > f40: 90 nop > #######sp:(und) bp:(und) type:call end:0 > f41: 90 nop > f42: 90 nop > #######sp:sp+8 bp:(und) type:iret end:0 > f43: e8 a8 01 00 00 callq 10f0 <error_entry> > #######sp:sp+0 bp:(und) type:regs end:0 > f48: f6 84 24 88 00 00 00 testb $0x3,0x88(%rsp) > f4f: 03 > f50: 74 00 je f52 <general_protection+0x12> > f52: 48 89 e7 mov %rsp,%rdi > f55: 48 8b 74 24 78 mov 0x78(%rsp),%rsi > f5a: 48 c7 44 24 78 ff ff movq $0xffffffffffffffff,0x78(%rsp) > f61: ff ff > f63: e8 00 00 00 00 callq f68 <general_protection+0x28> > f68: e9 73 02 00 00 jmpq 11e0 <error_exit> > #######sp:(und) bp:(und) type:call end:0 > f6d: 0f 1f 00 nopl (%rax) > > Note the entry at 0xf41. Josh found this was the result of commit: > > 764eef4b109a ("objtool: Rewrite alt->skip_orig") > > Due to the early return in validate_branch() we no longer set > insn->cfi of the original instruction stream (the NOPs at 0xf41 and > 0xf42) and we'll end up with the above weirdness. > > In other discussions we realized alternatives should be ORC invariant; > that is, due to there being only a single ORC table, it must be valid > for all alternatives. The easiest way to ensure this is to not allow > any stack modifications in alternatives. > > When we enforce this latter observation, we get the property that the > whole alternative must have the same CFI, which we can employ to fix > the former report. > > Fixes: 764eef4b109a ("objtool: Rewrite alt->skip_orig") > Reported-by: Jann Horn <jannh@google.com> > Signed-off-by: Peter Zijlstra (Intel) <peterz@infradead.org> > --- > tools/objtool/Documentation/stack-validation.txt | 7 ++++ > tools/objtool/check.c | 34 ++++++++++++++++++++++- > 2 files changed, 40 insertions(+), 1 deletion(-) > > --- a/tools/objtool/Documentation/stack-validation.txt > +++ b/tools/objtool/Documentation/stack-validation.txt > @@ -315,6 +315,13 @@ they mean, and suggestions for how to fi > function tracing inserts additional calls, which is not obvious from the > sources). > > +10. file.o: warning: func()+0x5c: alternative modifies stack > + > + This means that an alternative includes instructions that modify the > + stack. The problem is that there is only one ORC unwind table, this means > + that the ORC unwind entries must be valid for each of the alternatives. > + The easiest way to enforce this is to ensure alternative do not contain
"alternatives"
Acked-by: Josh Poimboeuf <jpoimboe@redhat.com>
-- Josh
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