Messages in this thread | | | Date | Tue, 15 Sep 2020 10:43:04 +0200 | From | peterz@infradea ... | Subject | Re: [PATCH] x86/unwind/fp: Fix FP unwinding in ret_from_fork |
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On Mon, Sep 14, 2020 at 12:04:22PM -0500, Josh Poimboeuf wrote: > There have been some reports of "bad bp value" warnings printed by the > frame pointer unwinder: > > WARNING: kernel stack regs at 000000005bac7112 in sh:1014 has bad 'bp' value 0000000000000000 > > This warning happens when unwinding from an interrupt in > ret_from_fork(). If entry code gets interrupted, the state of the frame > pointer (rbp) may be undefined, which can confuse the unwinder, > resulting in warnings like the above. > > There's an in_entry_code() check which normally silences such warnings > for entry code. But in this case, ret_from_fork() is getting > interrupted. It recently got moved out of .entry.text, so the > in_entry_code() check no longer works. > > We could move it back into .entry.text, but that would break the noinstr > validation because of the call to schedule_tail(). > > Instead, initialize each new task's RBP to point to the task's entry > regs via an encoded frame pointer. That will allow the unwinder to > reach the end of the stack gracefully. > > Fixes: b9f6976bfb94 ("x86/entry/64: Move non entry code into .text section") > Reported-by: Naresh Kamboju <naresh.kamboju@linaro.org> > Reported-by: Logan Gunthorpe <logang@deltatee.com> > Signed-off-by: Josh Poimboeuf <jpoimboe@redhat.com>
Acked-by: Peter Zijlstra (Intel) <peterz@infradead.org>
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