[PATCH 4.19 164/168] ARM: 8992/1: Fix unwind_frame for clang-built kernels

Greg Kroah-Hartman
2020-08-17T17:20:15Z

From: Nathan Huckleberry <nhuck@google.com>

commit b4d5ec9b39f8b31d98f65bc5577b5d15d93795d7 upstream.

Since clang does not push pc and sp in function prologues, the current
implementation of unwind_frame does not work. By using the previous
frame's lr/fp instead of saved pc/sp we get valid unwinds on clang-built
kernels.

The bounds check on next frame pointer must be changed as well since
there are 8 less bytes between frames.

This fixes /proc/<pid>/stack.

Link: https://github.com/ClangBuiltLinux/linux/issues/912

Reported-by: Miles Chen <miles.chen@mediatek.com>
Tested-by: Miles Chen <miles.chen@mediatek.com>
Cc: stable@vger.kernel.org
Reviewed-by: Nick Desaulniers <ndesaulniers@google.com>
Signed-off-by: Nathan Huckleberry <nhuck@google.com>
Signed-off-by: Russell King <rmk+kernel@armlinux.org.uk>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

---
arch/arm/kernel/stacktrace.c | 24 ++++++++++++++++++++++++
1 file changed, 24 insertions(+)

--- a/arch/arm/kernel/stacktrace.c
+++ b/arch/arm/kernel/stacktrace.c
@@ -21,6 +21,19 @@
* A simple function epilogue looks like this:
* ldm sp, {fp, sp, pc}
*
+ * When compiled with clang, pc and sp are not pushed. A simple function
+ * prologue looks like this when built with clang:
+ *
+ * stmdb {..., fp, lr}
+ * add fp, sp, #x
+ * sub sp, sp, #y
+ *
+ * A simple function epilogue looks like this when built with clang:
+ *
+ * sub sp, fp, #x
+ * ldm {..., fp, pc}
+ *
+ *
* Note that with framepointer enabled, even the leaf functions have the same
* prologue and epilogue, therefore we can ignore the LR value in this case.
*/
@@ -33,6 +46,16 @@ int notrace unwind_frame(struct stackfra
low = frame->sp;
high = ALIGN(low, THREAD_SIZE);

+#ifdef CONFIG_CC_IS_CLANG
+ /* check current frame pointer is within bounds */
+ if (fp < low + 4 || fp > high - 4)
+ return -EINVAL;
+
+ frame->sp = frame->fp;
+ frame->fp = *(unsigned long *)(fp);
+ frame->pc = frame->lr;
+ frame->lr = *(unsigned long *)(fp + 4);
+#else
/* check current frame pointer is within bounds */
if (fp < low + 12 || fp > high - 4)
return -EINVAL;
@@ -41,6 +64,7 @@ int notrace unwind_frame(struct stackfra
frame->fp = *(unsigned long *)(fp - 12);
frame->sp = *(unsigned long *)(fp - 8);
frame->pc = *(unsigned long *)(fp - 4);
+#endif

return 0;
}