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Subject[PATCH v3 6/9] arm64: Recover kretprobe modified return address in stacktrace
Date
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@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);

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