Messages in this thread | | | Date | Fri, 5 Feb 2021 09:51:11 -0500 | From | Steven Rostedt <> | Subject | Re: [PATCH 1/2] x86/unwind/orc: Disable KASAN checking in the ORC unwinder, part 2 |
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On Fri, 5 Feb 2021 08:24:02 -0600 Josh Poimboeuf <jpoimboe@redhat.com> wrote:
> KASAN reserves "redzone" areas between stack frames in order to detect > stack overruns. A read or write to such an area triggers a KASAN > "stack-out-of-bounds" BUG. > > Normally, the ORC unwinder stays in-bounds and doesn't access the > redzone. But sometimes it can't find ORC metadata for a given > instruction. This can happen for code which is missing ORC metadata, or > for generated code. In such cases, the unwinder attempts to fall back > to frame pointers, as a best-effort type thing. > > This fallback often works, but when it doesn't, the unwinder can get > confused and go off into the weeds into the KASAN redzone, triggering > the aforementioned KASAN BUG. > > But in this case, the unwinder's confusion is actually harmless and > working as designed. It already has checks in place to prevent > off-stack accesses, but those checks get short-circuited by the KASAN > BUG. And a BUG is a lot more disruptive than a harmless unwinder > warning. > > Disable the KASAN checks by using READ_ONCE_NOCHECK() for all stack > accesses. This finishes the job started by commit 881125bfe65b > ("x86/unwind: Disable KASAN checking in the ORC unwinder"), which only > partially fixed the issue. > > Fixes: ee9f8fce9964 ("x86/unwind: Add the ORC unwinder") > Reported-by: Ivan Babrou <ivan@cloudflare.com> > Cc: stable@vger.kernel.org > Signed-off-by: Josh Poimboeuf <jpoimboe@redhat.com>
Reviewed-by: Steven Rostedt (VMware) <rostedt@goodmis.org>
-- Steve
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