path: root/kernel
diff options
authorJosh Poimboeuf <jpoimboe@redhat.com>2017-02-13 19:42:28 -0600
committerJiri Kosina <jkosina@suse.cz>2017-03-08 09:18:02 +0100
commitaf085d9084b48530153f51e6cad19fd0b1a13ed7 (patch)
tree9b8c658ddddfe29d76c5641e346e2d2224f75363 /kernel
parentc1ae3cfa0e89fa1a7ecc4c99031f5e9ae99d9201 (diff)
stacktrace/x86: add function for detecting reliable stack traces
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@redhat.com> Reviewed-by: Miroslav Benes <mbenes@suse.cz> Acked-by: Ingo Molnar <mingo@kernel.org> # for the x86 changes Signed-off-by: Jiri Kosina <jkosina@suse.cz>
Diffstat (limited to 'kernel')
1 files changed, 10 insertions, 2 deletions
diff --git a/kernel/stacktrace.c b/kernel/stacktrace.c
index 9c15a9124e83..f8edee9c792d 100644
--- a/kernel/stacktrace.c
+++ b/kernel/stacktrace.c
@@ -54,8 +54,8 @@ int snprint_stack_trace(char *buf, size_t size,
- * Architectures that do not implement save_stack_trace_tsk or
- * save_stack_trace_regs get this weak alias and a once-per-bootup warning
+ * Architectures that do not implement save_stack_trace_*()
+ * get these weak aliases and once-per-bootup warnings
* (whenever this facility is utilized - for example by procfs):
__weak void
@@ -69,3 +69,11 @@ save_stack_trace_regs(struct pt_regs *regs, struct stack_trace *trace)
WARN_ONCE(1, KERN_INFO "save_stack_trace_regs() not implemented yet.\n");
+__weak int
+save_stack_trace_tsk_reliable(struct task_struct *tsk,
+ struct stack_trace *trace)
+ WARN_ONCE(1, KERN_INFO "save_stack_tsk_reliable() not implemented yet.\n");
+ return -ENOSYS;

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