On Mon, 2017-02-13 at 19:42 -0600, Josh Poimboeuf wrote: > 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: Josh Poimboeuf <jpoimboe@xxxxxxxxxx> > --- Could you comment on why we need a reliable trace for live-patching? Are we in any way reliant on the stack trace to patch something broken? Thanks, Balbir Singh. -- To unsubscribe from this list: send the line "unsubscribe linux-s390" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
