• Josh Poimboeuf's avatar
    stacktrace/x86: add function for detecting reliable stack traces · af085d90
    Josh Poimboeuf authored
    For live patching and possibly other use cases, a stack trace is only
    useful if it can be assured that it's completely reliable.  Add a new
    save_stack_trace_tsk_reliable() function to achieve that.
    Note that if the target task isn't the current task, and the target task
    is allowed to run, then it could be writing the stack while the unwinder
    is reading it, resulting in possible corruption.  So the caller of
    save_stack_trace_tsk_reliable() must ensure that the task is either
    'current' or inactive.
    save_stack_trace_tsk_reliable() relies on the x86 unwinder's detection
    of pt_regs on the stack.  If the pt_regs are not user-mode registers
    from a syscall, then they indicate an in-kernel interrupt or exception
    (e.g. preemption or a page fault), in which case the stack is considered
    unreliable due to the nature of frame pointers.
    It also relies on the x86 unwinder's detection of other issues, such as:
    - corrupted stack data
    - stack grows the wrong way
    - stack walk doesn't reach the bottom
    - user didn't provide a large enough entries array
    Such issues are reported by checking unwind_error() and !unwind_done().
    Also add CONFIG_HAVE_RELIABLE_STACKTRACE so arch-independent code can
    determine at build time whether the function is implemented.
    Signed-off-by: default avatarJosh Poimboeuf <jpoimboe@redhat.com>
    Reviewed-by: default avatarMiroslav Benes <mbenes@suse.cz>
    Acked-by: Ingo Molnar <mingo@kernel.org>	# for the x86 changes
    Signed-off-by: default avatarJiri Kosina <jkosina@suse.cz>