Re: [PATCH 1/3] stackleak: mark stackleak_track_stack() as notrace

[Kees Cook]

On Fri, Nov 30, 2018 at 7:09 AM Anders Roxell <anders.roxell@xxxxxxxxxx> wrote:
>
> Function graph tracing recurses into itself when stackleak is enabled,
> causing the ftrace graph selftest to run for up to 90 seconds and
> trigger the softlockup watchdog.
>
> Breakpoint 2, ftrace_graph_caller () at ../arch/arm64/kernel/entry-ftrace.S:200
> 200             mcount_get_lr_addr        x0    //     pointer to function's saved lr
> (gdb) bt
> \#0  ftrace_graph_caller () at ../arch/arm64/kernel/entry-ftrace.S:200
> \#1  0xffffff80081d5280 in ftrace_caller () at ../arch/arm64/kernel/entry-ftrace.S:153
> \#2  0xffffff8008555484 in stackleak_track_stack () at ../kernel/stackleak.c:106
> \#3  0xffffff8008421ff8 in ftrace_ops_test (ops=0xffffff8009eaa840 <graph_ops>, ip=18446743524091297036, regs=<optimized out>) at ../kernel/trace/ftrace.c:1507
> \#4  0xffffff8008428770 in __ftrace_ops_list_func (regs=<optimized out>, ignored=<optimized out>, parent_ip=<optimized out>, ip=<optimized out>) at ../kernel/trace/ftrace.c:6286
> \#5  ftrace_ops_no_ops (ip=18446743524091297036, parent_ip=18446743524091242824) at ../kernel/trace/ftrace.c:6321
> \#6  0xffffff80081d5280 in ftrace_caller () at ../arch/arm64/kernel/entry-ftrace.S:153
> \#7  0xffffff800832fd10 in irq_find_mapping (domain=0xffffffc03fc4bc80, hwirq=27) at ../kernel/irq/irqdomain.c:876
> \#8  0xffffff800832294c in __handle_domain_irq (domain=0xffffffc03fc4bc80, hwirq=27, lookup=true, regs=0xffffff800814b840) at ../kernel/irq/irqdesc.c:650
> \#9  0xffffff80081d52b4 in ftrace_graph_caller () at ../arch/arm64/kernel/entry-ftrace.S:205
>
> Rework so we mark stackleak_track_stack as notrace
>
> Co-developed-by: Arnd Bergmann <arnd@xxxxxxxx>
> Signed-off-by: Arnd Bergmann <arnd@xxxxxxxx>
> Signed-off-by: Anders Roxell <anders.roxell@xxxxxxxxxx>
> ---
>  kernel/stackleak.c | 2 +-
>  1 file changed, 1 insertion(+), 1 deletion(-)
>
> diff --git a/kernel/stackleak.c b/kernel/stackleak.c
> index e42892926244..5de3bf596dd7 100644
> --- a/kernel/stackleak.c
> +++ b/kernel/stackleak.c
> @@ -102,7 +102,7 @@ asmlinkage void stackleak_erase(void)
>         current->lowest_stack = current_top_of_stack() - THREAD_SIZE/64;
>  }
>
> -void __used stackleak_track_stack(void)
> +void __used notrace stackleak_track_stack(void)
>  {
>         /*
>          * N.B. stackleak_erase() fills the kernel stack with the poison value,
> --
> 2.19.2
>

Acked-by: Kees Cook <keescook@xxxxxxxxxxxx>

Steven, I assume this series going via your tree?

-- 
Kees Cook