Mailing List Archive

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

Reported-by: Naresh Kamboju <naresh.kamboju@linaro.org>
Signed-off-by: Masami Hiramatsu <mhiramat@kernel.org>
---
arch/arm64/kernel/return_address.c | 4 +++-
arch/arm64/kernel/stacktrace.c | 3 +++
2 files changed, 6 insertions(+), 1 deletion(-)

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)
{
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);
diff --git a/arch/arm64/kernel/stacktrace.c b/arch/arm64/kernel/stacktrace.c
index 62d395151abe..cd7dab54d17b 100644
--- a/arch/arm64/kernel/stacktrace.c
+++ b/arch/arm64/kernel/stacktrace.c
@@ -7,6 +7,7 @@
#include <linux/kernel.h>
#include <linux/export.h>
#include <linux/ftrace.h>
+#include <linux/kprobes.h>
#include <linux/sched.h>
#include <linux/sched/debug.h>
#include <linux/sched/task_stack.h>
@@ -73,6 +74,7 @@ int notrace unwind_frame(struct task_struct *tsk, struct stackframe *frame)

return 0;
}
+NOKPROBE_SYMBOL(unwind_frame);

void notrace walk_stackframe(struct task_struct *tsk, struct stackframe *frame,
int (*fn)(struct stackframe *, void *), void *data)
@@ -87,6 +89,7 @@ void notrace walk_stackframe(struct task_struct *tsk, struct stackframe *frame,
break;
}
}
+NOKPROBE_SYMBOL(walk_stackframe);

#ifdef CONFIG_STACKTRACE
struct stack_trace_data {
Re: [PATCH v2 2/4] arm64: unwind: Prohibit probing on return_address() [ In reply to ]
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")


> 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!

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


> {
> 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
Re: [PATCH v2 2/4] arm64: unwind: Prohibit probing on return_address() [ In reply to ]
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>