ARM: unwind: dump exception stack from calling frame

The existing code that dumps the contents of the pt_regs structure
passed to __entry routines does so while unwinding the callee frame, and
dereferences the stack pointer as a struct pt_regs*. This will no longer
work when we enable support for IRQ or overflow stacks, because the
struct pt_regs may live on the task stack, while we are executing from
another stack.

The unwinder has access to this information, but only while unwinding
the calling frame. So let's combine the exception stack dumping code
with the handling of the calling frame as well. By printing it before
dumping the caller/callee addresses, the output order is preserved.

Signed-off-by: Ard Biesheuvel <ardb@kernel.org>
Reviewed-by: Arnd Bergmann <arnd@arndb.de>
Acked-by: Linus Walleij <linus.walleij@linaro.org>
Tested-by: Keith Packard <keithpac@amazon.com>
Tested-by: Marc Zyngier <maz@kernel.org>
Tested-by: Vladimir Murzin <vladimir.murzin@arm.com> # ARMv7M

diff --git a/arch/arm/include/asm/stacktrace.h b/arch/arm/include/asm/stacktrace.h
index 33ee1aa4b8c0edf6213b196447dace8368ef2e7e..d87d60532b867ef6f0a6ed4833156f0f8a1cf02c 100644 (file)
--- a/arch/arm/include/asm/stacktrace.h
+++ b/arch/arm/include/asm/stacktrace.h
@@ -18,6 +18,16 @@ struct stackframe {
        struct llist_node *kr_cur;
        struct task_struct *tsk;
 #endif
+#ifdef CONFIG_ARM_UNWIND
+       /*
+        * This field is used to track the stack pointer value when calling
+        * __entry routines. This is needed when IRQ stacks and overflow stacks
+        * are used, because in that case, the struct pt_regs passed to these
+        * __entry routines may be at the top of the task stack, while we are
+        * executing from another stack.
+        */
+       unsigned long sp_low;
+#endif
 };
 
 static __always_inline

diff --git a/arch/arm/kernel/traps.c b/arch/arm/kernel/traps.c
index e4698605bb724e082c92d85a36fdc48227f8f16b..89be21ec3b521b123afea5be20f1f66ce49faf7f 100644 (file)
--- a/arch/arm/kernel/traps.c
+++ b/arch/arm/kernel/traps.c
@@ -74,7 +74,8 @@ void dump_backtrace_entry(unsigned long where, unsigned long from,
                loglvl, where, from);
 #endif
 
-       if (in_entry_text(from) && end <= ALIGN(frame, THREAD_SIZE))
+       if (!IS_ENABLED(CONFIG_UNWINDER_ARM) &&
+           in_entry_text(from) && end <= ALIGN(frame, THREAD_SIZE))
                dump_mem(loglvl, "Exception stack", frame + 4, end);
 }
 

diff --git a/arch/arm/kernel/unwind.c b/arch/arm/kernel/unwind.c
index 9cb9af3fc43398c43b294108e815afe1da7ed18a..b7a6141c342fc3ef175ba96ebc915293b21517bf 100644 (file)
--- a/arch/arm/kernel/unwind.c
+++ b/arch/arm/kernel/unwind.c
@@ -29,6 +29,7 @@
 #include <linux/spinlock.h>
 #include <linux/list.h>
 
+#include <asm/sections.h>
 #include <asm/stacktrace.h>
 #include <asm/traps.h>
 #include <asm/unwind.h>
@@ -459,6 +460,7 @@ int unwind_frame(struct stackframe *frame)
        frame->sp = ctrl.vrs[SP];
        frame->lr = ctrl.vrs[LR];
        frame->pc = ctrl.vrs[PC];
+       frame->sp_low = ctrl.sp_low;
 
        return URC_OK;
 }
@@ -502,7 +504,11 @@ void unwind_backtrace(struct pt_regs *regs, struct task_struct *tsk,
                urc = unwind_frame(&frame);
                if (urc < 0)
                        break;
-               dump_backtrace_entry(where, frame.pc, frame.sp - 4, loglvl);
+               if (in_entry_text(where))
+                       dump_mem(loglvl, "Exception stack", frame.sp_low,
+                                frame.sp_low + sizeof(struct pt_regs));
+
+               dump_backtrace_entry(where, frame.pc, 0, loglvl);
        }
 }