[PATCH v3 6/9] arm64: Recover kretprobe modified return address in stacktrace

[Masami Hiramatsu]

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. For this purpose
this adds 'kr_cur' loop cursor to memorize the current kretprobe
instance.

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 at kernel.org>
---
 Changes in v2:
  - Add comment for kr_cur.
  - Make the kretprobe related code depends on CONFIG_KRETPROBES.
  - Initialize "kr_cur" directly in start_backtrace() instead
    of clearing "frame" data structure by memset().
---
 arch/arm64/Kconfig                  |    1 +
 arch/arm64/include/asm/stacktrace.h |    4 ++++
 arch/arm64/kernel/stacktrace.c      |    7 +++++++
 3 files changed, 12 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..a4e046ef4568 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 +60,9 @@ struct stackframe {
 #ifdef CONFIG_FUNCTION_GRAPH_TRACER
 	int graph;
 #endif
+#ifdef CONFIG_KRETPROBES
+	struct llist_node *kr_cur;
+#endif
 };
 
 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..c30624fff6ac 100644
--- a/arch/arm64/kernel/stacktrace.c
+++ b/arch/arm64/kernel/stacktrace.c
@@ -41,6 +41,9 @@ void start_backtrace(struct stackframe *frame, unsigned long fp,
 #ifdef CONFIG_FUNCTION_GRAPH_TRACER
 	frame->graph = 0;
 #endif
+#ifdef CONFIG_KRETPROBES
+	frame->kr_cur = NULL;
+#endif
 
 	/*
 	 * Prime the first unwind.
@@ -129,6 +132,10 @@ int notrace unwind_frame(struct task_struct *tsk, struct stackframe *frame)
 		frame->pc = ret_stack->ret;
 	}
 #endif /* CONFIG_FUNCTION_GRAPH_TRACER */
+#ifdef CONFIG_KRETPROBES
+	if (is_kretprobe_trampoline(frame->pc))
+		frame->pc = kretprobe_find_ret_addr(tsk, (void *)frame->fp, &frame->kr_cur);
+#endif
 
 	frame->pc = ptrauth_strip_insn_pac(frame->pc);