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

Masami Hiramatsu
2021-10-08T12:36:10Z

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;
};

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));
if (regs)
start_backtrace(&frame, regs->regs[29], regs->pc);
else if (task == current)