Re: [PATCH v2 2/4] arm64: unwind: Prohibit probing on return_address()

Masami Hiramatsu
2019-07-24T07:39:29Z

On Tue, 23 Jul 2019 17:04:21 +0100
James Morse <james.morse@arm.com> wrote:

> Hi,
>
> On 22/07/2019 08:48, Masami Hiramatsu wrote:
> > Prohibit probing on return_address() and subroutines which
> > is called from return_address(), since the it is invoked from
> > trace_hardirqs_off() which is also kprobe blacklisted.
>
> (Nits: "which are called" and "since it is")

Thanks!

>
>
> > diff --git a/arch/arm64/kernel/return_address.c b/arch/arm64/kernel/return_address.c
> > index b21cba90f82d..7f8a143268b0 100644
> > --- a/arch/arm64/kernel/return_address.c
> > +++ b/arch/arm64/kernel/return_address.c
> > @@ -8,6 +8,7 @@
> >
> > #include <linux/export.h>
> > #include <linux/ftrace.h>
> > +#include <linux/kprobes.h>
> >
> > #include <asm/stack_pointer.h>
> > #include <asm/stacktrace.h>
> > @@ -17,7 +18,7 @@ struct return_address_data {
> > void *addr;
> > };
> >
> > -static int save_return_addr(struct stackframe *frame, void *d)
> > +static nokprobe_inline int save_return_addr(struct stackframe *frame, void *d)
>
> This nokprobe_inline ends up as __always_inline if kprobes is enabled.
> What do we expect the compiler to do with this? save_return_addr is passed as a
> function-pointer to walk_stackframe()... I don't see how the compiler can inline it!

Oops, that's my mistake. Then it should be NOKPROBE_SYMBOL.

>
> This would be needed for on_accessible_stack().
> Should we cover ftrace_graph_get_ret_stack()?, or is that already in hand?

No, that is OK. It just covers that the functions which are involved in
the kprobe execution path. ftrace_graph_ret_stack() is out of the debug
exception handler.

Thank you,

> > {
> > struct return_address_data *data = d;
> >
> > @@ -52,3 +53,4 @@ void *return_address(unsigned int level)
> > return NULL;
> > }
> > EXPORT_SYMBOL_GPL(return_address);
> > +NOKPROBE_SYMBOL(return_address);
>
>
> Thanks,
>
> James

--
Masami Hiramatsu <mhiramat@kernel.org>