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

[Masami Hiramatsu <mhiramat@kernel.org>]

On Wed, 13 Oct 2021 09:14:16 +0100
Will Deacon <will@kernel.org> wrote:

> 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.

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,

> 
> >  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 <mhiramat@kernel.org>

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