Re: [PATCH 5/8] arm64: Recover kretprobe modified return address in stacktrace

On Wed, 13 Oct 2021 09:14:16 +0100
Will Deacon [off-list ref] wrote:

On Fri, Oct 08, 2021 at 09:28:58PM +0900, Masami Hiramatsu wrote:

quoted

Since the kretprobe replaces the function return address with
the kretprobe_trampoline on the stack, stack unwinder shows it
instead of the correct return address.

This checks whether the next return address is the
__kretprobe_trampoline(), and if so, try to find the correct
return address from the kretprobe instance list.

With this fix, now arm64 can enable
CONFIG_ARCH_CORRECT_STACKTRACE_ON_KRETPROBE, and pass the
kprobe self tests.

Signed-off-by: Masami Hiramatsu <mhiramat@kernel.org>
---
 arch/arm64/Kconfig                  |    1 +
 arch/arm64/include/asm/stacktrace.h |    2 ++
 arch/arm64/kernel/stacktrace.c      |    3 +++
 3 files changed, 6 insertions(+)

diff --git a/arch/arm64/Kconfig b/arch/arm64/Kconfig
index 5c7ae4c3954b..edde5171ffb2 100644
--- a/arch/arm64/Kconfig
+++ b/arch/arm64/Kconfig

@@ -11,6 +11,7 @@ config ARM64
 	select ACPI_PPTT if ACPI
 	select ARCH_HAS_DEBUG_WX
 	select ARCH_BINFMT_ELF_STATE
+	select ARCH_CORRECT_STACKTRACE_ON_KRETPROBE
 	select ARCH_ENABLE_HUGEPAGE_MIGRATION if HUGETLB_PAGE && MIGRATION
 	select ARCH_ENABLE_MEMORY_HOTPLUG
 	select ARCH_ENABLE_MEMORY_HOTREMOVE

diff --git a/arch/arm64/include/asm/stacktrace.h b/arch/arm64/include/asm/stacktrace.h
index 8aebc00c1718..8f997a602651 100644
--- a/arch/arm64/include/asm/stacktrace.h
+++ b/arch/arm64/include/asm/stacktrace.h

@@ -9,6 +9,7 @@
 #include <linux/sched.h>
 #include <linux/sched/task_stack.h>
 #include <linux/types.h>
+#include <linux/llist.h>
 
 #include <asm/memory.h>
 #include <asm/ptrace.h>

@@ -59,6 +60,7 @@ struct stackframe {
 #ifdef CONFIG_FUNCTION_GRAPH_TRACER
 	int graph;
 #endif
+	struct llist_node *kr_cur;
 };

Please update the comment above this structure to describe the new member
you're adding.

OK, let me update that. 

If it's only relevant for kprobes, then let's define it
conditionally too (based on CONFIG_KRETPROBES ?)

Ah, good point! Yes, it must be only valid when CONFIG_KRETPROBES=y.

Thank you,

quoted

 extern int unwind_frame(struct task_struct *tsk, struct stackframe *frame);

diff --git a/arch/arm64/kernel/stacktrace.c b/arch/arm64/kernel/stacktrace.c
index 8982a2b78acf..f1eef5745542 100644
--- a/arch/arm64/kernel/stacktrace.c
+++ b/arch/arm64/kernel/stacktrace.c

@@ -129,6 +129,8 @@ int notrace unwind_frame(struct task_struct *tsk, struct stackframe *frame)
 		frame->pc = ret_stack->ret;
 	}
 #endif /* CONFIG_FUNCTION_GRAPH_TRACER */
+	if (is_kretprobe_trampoline(frame->pc))
+		frame->pc = kretprobe_find_ret_addr(tsk, (void *)frame->fp, &frame->kr_cur);
 
 	frame->pc = ptrauth_strip_insn_pac(frame->pc);
 

@@ -224,6 +226,7 @@ noinline notrace void arch_stack_walk(stack_trace_consume_fn consume_entry,
 {
 	struct stackframe frame;
 
+	memset(&frame, 0, sizeof(frame));

Why do we need this?

Will

-- 
Masami Hiramatsu [off-list ref]

_______________________________________________
linux-arm-kernel mailing list
linux-arm-kernel@lists.infradead.org
http://lists.infradead.org/mailman/listinfo/linux-arm-kernel