From: "Steven Rostedt (Google)" <[email protected]>
In function_graph_enter() there's a loop that looks at fgraph_array[]
elements which are fgraph_ops. It first tests if it is a fgraph_stub op,
and if so skips it, as that's just there as a place holder. Then it checks
the fgraph_ops filters to see if the ops wants to trace the current
function.
But if the compiler reloads the fgraph_array[] after the check against
fgraph_stub, it could race with the fgraph_array[] being updated with the
fgraph_stub. That would cause the stub to be processed. But the stub has a
null "func_hash" field which will cause a NULL pointer dereference.
Add a READ_ONCE() so that the gops that is compared against the
fgraph_stub is also the gops that is processed later.
Link: https://lore.kernel.org/all/CA+G9fYsSVJQZH=nM=1cjTc94PgSnMF9y65BnOv6XSoCG_b6wmw@mail.gmail.com/
Fixes: cc60ee813b503 ("function_graph: Use static_call and branch to optimize entry function")
Reported-by: Naresh Kamboju <[email protected]>
Signed-off-by: Steven Rostedt (Google) <[email protected]>
---
kernel/trace/fgraph.c | 2 +-
1 file changed, 1 insertion(+), 1 deletion(-)
diff --git a/kernel/trace/fgraph.c b/kernel/trace/fgraph.c
index 8317d1a7f43a..fc205ad167a9 100644
--- a/kernel/trace/fgraph.c
+++ b/kernel/trace/fgraph.c
@@ -641,7 +641,7 @@ int function_graph_enter(unsigned long ret, unsigned long func,
{
for_each_set_bit(i, &fgraph_array_bitmask,
sizeof(fgraph_array_bitmask) * BITS_PER_BYTE) {
- struct fgraph_ops *gops = fgraph_array[i];
+ struct fgraph_ops *gops = READ_ONCE(fgraph_array[i]);
int save_curr_ret_stack;
if (gops == &fgraph_stub)
--
2.43.0
On Thu, 13 Jun 2024 09:52:23 -0400
Steven Rostedt <[email protected]> wrote:
> From: "Steven Rostedt (Google)" <[email protected]>
>
> In function_graph_enter() there's a loop that looks at fgraph_array[]
> elements which are fgraph_ops. It first tests if it is a fgraph_stub op,
> and if so skips it, as that's just there as a place holder. Then it checks
> the fgraph_ops filters to see if the ops wants to trace the current
> function.
>
> But if the compiler reloads the fgraph_array[] after the check against
> fgraph_stub, it could race with the fgraph_array[] being updated with the
> fgraph_stub. That would cause the stub to be processed. But the stub has a
> null "func_hash" field which will cause a NULL pointer dereference.
>
> Add a READ_ONCE() so that the gops that is compared against the
> fgraph_stub is also the gops that is processed later.
>
> Link: https://lore.kernel.org/all/CA+G9fYsSVJQZH=nM=1cjTc94PgSnMF9y65BnOv6XSoCG_b6wmw@mail.gmail.com/
>
> Fixes: cc60ee813b503 ("function_graph: Use static_call and branch to optimize entry function")
> Reported-by: Naresh Kamboju <[email protected]>
> Signed-off-by: Steven Rostedt (Google) <[email protected]>
Looks good to me.
Acked-by: Masami Hiramatsu (Google) <[email protected]>
Thanks.
> ---
> kernel/trace/fgraph.c | 2 +-
> 1 file changed, 1 insertion(+), 1 deletion(-)
>
> diff --git a/kernel/trace/fgraph.c b/kernel/trace/fgraph.c
> index 8317d1a7f43a..fc205ad167a9 100644
> --- a/kernel/trace/fgraph.c
> +++ b/kernel/trace/fgraph.c
> @@ -641,7 +641,7 @@ int function_graph_enter(unsigned long ret, unsigned long func,
> {
> for_each_set_bit(i, &fgraph_array_bitmask,
> sizeof(fgraph_array_bitmask) * BITS_PER_BYTE) {
> - struct fgraph_ops *gops = fgraph_array[i];
> + struct fgraph_ops *gops = READ_ONCE(fgraph_array[i]);
> int save_curr_ret_stack;
>
> if (gops == &fgraph_stub)
> --
> 2.43.0
>
--
Masami Hiramatsu (Google) <[email protected]>