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    SubjectRe: [PATCH 5/8] arm64: Recover kretprobe modified return address in stacktrace
    On Fri, Oct 08, 2021 at 09:28:58PM +0900, Masami Hiramatsu wrote:
    > 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. If it's only relevant for kprobes, then let's define it
    conditionally too (based on CONFIG_KRETPROBES ?)

    > 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

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