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authorJosh Poimboeuf <jpoimboe@redhat.com>2020-09-14 12:04:22 -0500
committerBorislav Petkov <bp@suse.de>2020-09-18 09:59:40 +0200
commit6f9885a36c006d798319661fa849f9c2922223b9 (patch)
treef250754415076a6bf48348ec8f96858763125bfe /arch/x86/configs
parent09e43968db40c33a73e9ddbfd937f46d5c334924 (diff)
downloadlinux-6f9885a36c006d798319661fa849f9c2922223b9.tar.bz2
x86/unwind/fp: Fix FP unwinding in ret_from_fork
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. It could be moved 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> Signed-off-by: Borislav Petkov <bp@suse.de> Acked-by: Peter Zijlstra (Intel) <peterz@infradead.org> Acked-by: Thomas Gleixner <tglx@linutronix.de> Link: https://lkml.kernel.org/r/f366bbf5a8d02e2318ee312f738112d0af74d16f.1600103007.git.jpoimboe@redhat.com
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