The bottom-most stack frame (the first to be unwound) may be largely
uninitialized, for the "Power Architecture 64-Bit ELF V2 ABI" only
requires its backchain pointer to be set.
The reliable stack tracer should be careful when verifying this frame:
skip checks on STACK_FRAME_LR_SAVE and STACK_FRAME_MARKER offsets that
may contain uninitialized residual data.
Fixes: df78d3f61480 ("powerpc/livepatch: Implement reliable stack tracing for
the consistency model")
Signed-off-by: Joe Lawrence <joe.lawre...@redhat.com>
---
arch/powerpc/kernel/stacktrace.c | 32 ++++++++++++++++++++++++--------
1 file changed, 24 insertions(+), 8 deletions(-)
diff --git a/arch/powerpc/kernel/stacktrace.c b/arch/powerpc/kernel/stacktrace.c
index e2c50b55138f..06688f4d557b 100644
--- a/arch/powerpc/kernel/stacktrace.c
+++ b/arch/powerpc/kernel/stacktrace.c
@@ -84,6 +84,12 @@ save_stack_trace_regs(struct pt_regs *regs, struct
stack_trace *trace)
EXPORT_SYMBOL_GPL(save_stack_trace_regs);
#ifdef CONFIG_HAVE_RELIABLE_STACKTRACE
+/*
+ * This function returns an error if it detects any unreliable features of the
+ * stack. Otherwise it guarantees that the stack trace is reliable.
+ *
+ * If the task is not 'current', the caller *must* ensure the task is inactive.
+ */
int
save_stack_trace_tsk_reliable(struct task_struct *tsk,
struct stack_trace *trace)
@@ -142,12 +148,6 @@ save_stack_trace_tsk_reliable(struct task_struct *tsk,
if (sp & 0xF)
return 1;
- /* Mark stacktraces with exception frames as unreliable. */
- if (sp <= stack_end - STACK_INT_FRAME_SIZE &&
- stack[STACK_FRAME_MARKER] == STACK_FRAME_REGS_MARKER) {
- return 1;
- }
-
newsp = stack[0];
/* Stack grows downwards; unwinder may only go up. */
if (newsp <= sp)
@@ -158,11 +158,26 @@ save_stack_trace_tsk_reliable(struct task_struct *tsk,
return 1; /* invalid backlink, too far up. */
}
+ /*
+ * We can only trust the bottom frame's backlink, the
+ * rest of the frame may be uninitialized, continue to
+ * the next.
+ */
+ if (firstframe) {
+ firstframe = 0;
+ goto next;
+ }
+
+ /* Mark stacktraces with exception frames as unreliable. */
+ if (sp <= stack_end - STACK_INT_FRAME_SIZE &&
+ stack[STACK_FRAME_MARKER] == STACK_FRAME_REGS_MARKER) {
+ return 1;
+ }
+
/* Examine the saved LR: it must point into kernel code. */
ip = stack[STACK_FRAME_LR_SAVE];
- if (!firstframe && !__kernel_text_address(ip))
+ if (!__kernel_text_address(ip))
return 1;
- firstframe = 0;
/*
* FIXME: IMHO these tests do not belong in
@@ -183,6 +198,7 @@ save_stack_trace_tsk_reliable(struct task_struct *tsk,
else
trace->skip--;
+next:
if (newsp == stack_end)
break;
--
2.20.1
