• Josh Poimboeuf's avatar
    x86/entry/unwind: Create stack frames for saved interrupt registers · 946c1911
    Josh Poimboeuf authored
    With frame pointers, when a task is interrupted, its stack is no longer
    completely reliable because the function could have been interrupted
    before it had a chance to save the previous frame pointer on the stack.
    So the caller of the interrupted function could get skipped by a stack
    trace.
    
    This is problematic for live patching, which needs to know whether a
    stack trace of a sleeping task can be relied upon.  There's currently no
    way to detect if a sleeping task was interrupted by a page fault
    exception or preemption before it went to sleep.
    
    Another issue is that when dumping the stack of an interrupted task, the
    unwinder has no way of knowing where the saved pt_regs registers are, so
    it can't print them.
    
    This solves those issues by encoding the pt_regs pointer in the frame
    pointer on entry from an interrupt or an exception.
    
    This patch also updates the unwinder to be able to decode it, because
    otherwise the unwinder would be broken by this change.
    
    Note that this causes a change in the behavior of the unwinder: each
    instance of a pt_regs on the stack is now considered a "frame".  So
    callers of unwind_get_return_address() will now get an occasional
    'regs->ip' address that would have previously been skipped over.
    Suggested-by: default avatarAndy Lutomirski <luto@amacapital.net>
    Signed-off-by: default avatarJosh Poimboeuf <jpoimboe@redhat.com>
    Cc: Andy Lutomirski <luto@kernel.org>
    Cc: Borislav Petkov <bp@alien8.de>
    Cc: Brian Gerst <brgerst@gmail.com>
    Cc: Denys Vlasenko <dvlasenk@redhat.com>
    Cc: H. Peter Anvin <hpa@zytor.com>
    Cc: Linus Torvalds <torvalds@linux-foundation.org>
    Cc: Peter Zijlstra <peterz@infradead.org>
    Cc: Thomas Gleixner <tglx@linutronix.de>
    Link: http://lkml.kernel.org/r/8b9f84a21e39d249049e0547b559ff8da0df0988.1476973742.git.jpoimboe@redhat.comSigned-off-by: default avatarIngo Molnar <mingo@kernel.org>
    946c1911
entry_32.S 29.5 KB