https://github.com/torvalds/linux
Revision 519fb5c3350d1b5225b27b1cac55144f79351718 authored by Josh Poimboeuf on 23 May 2017, 15:37:30 UTC, committed by Ingo Molnar on 24 May 2017, 07:05:16 UTC
Dave Jones and Steven Rostedt reported unwinder warnings like the following: WARNING: kernel stack frame pointer at ffff8800bda0ff30 in sshd:1090 has bad value 000055b32abf1fa8 In both cases, the unwinder was attempting to unwind from an ftrace handler into entry code. The callchain was something like: syscall entry code C function ftrace handler save_stack_trace() The problem is that the unwinder's end-of-stack logic gets confused by the way ftrace lays out the stack frame (with fentry enabled). I was able to recreate this warning with: echo call_usermodehelper_exec_async:stacktrace > /sys/kernel/debug/tracing/set_ftrace_filter (exit login session) I considered fixing this by changing the ftrace code to rewrite the stack to make the unwinder happy. But that seemed too intrusive after I implemented it. Instead, just add another check to the unwinder's end-of-stack logic to detect this special case. Side note: We could probably get rid of these end-of-stack checks by encoding the frame pointer for syscall entry just like we do for interrupt entry. That would be simpler, but it would also be a lot more intrusive since it would slightly affect the performance of every syscall. Reported-by: Dave Jones <davej@codemonkey.org.uk> Reported-by: Steven Rostedt <rostedt@goodmis.org> Signed-off-by: Josh Poimboeuf <jpoimboe@redhat.com> Acked-by: Thomas Gleixner <tglx@linutronix.de> Cc: Linus Torvalds <torvalds@linux-foundation.org> Cc: Peter Zijlstra <peterz@infradead.org> Cc: Petr Mladek <pmladek@suse.com> Cc: live-patching@vger.kernel.org Fixes: c32c47c68a0a ("x86/unwind: Warn on bad frame pointer") Link: http://lkml.kernel.org/r/671ba22fbc0156b8f7e0cfa5ab2a795e08bc37e1.1495553739.git.jpoimboe@redhat.com Signed-off-by: Ingo Molnar <mingo@kernel.org>
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Tip revision: 519fb5c3350d1b5225b27b1cac55144f79351718 authored by Josh Poimboeuf on 23 May 2017, 15:37:30 UTC
x86/unwind: Add end-of-stack check for ftrace handlers
x86/unwind: Add end-of-stack check for ftrace handlers
Tip revision: 519fb5c
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Makefile | -rw-r--r-- | 58.6 KB |
README | -rw-r--r-- | 722 bytes |
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