2020-11-06 02:39:25

by Steven Rostedt

Subject: [PATCH 07/11 v3] livepatch: Trigger WARNING if livepatch function fails due to recursion

From: "Steven Rostedt (VMware)" <[email protected]>

If for some reason a function is called that triggers the recursion
detection of live patching, trigger a warning. By not executing the live
patch code, it is possible that the old unpatched function will be called
placing the system into an unknown state.

Link: https://lore.kernel.org/r/20201029145709.GD16774@alley

Cc: Josh Poimboeuf <[email protected]>
Cc: Jiri Kosina <[email protected]>
Cc: Joe Lawrence <[email protected]>
Cc: [email protected]
Suggested-by: Miroslav Benes <[email protected]>
Reviewed-by: Petr Mladek <[email protected]>
Signed-off-by: Steven Rostedt (VMware) <[email protected]>
---
Changes since v2:

- Blame Miroslav instead of Petr ;-)

kernel/livepatch/patch.c | 2 +-
1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/kernel/livepatch/patch.c b/kernel/livepatch/patch.c
index 6c0164d24bbd..15480bf3ce88 100644
--- a/kernel/livepatch/patch.c
+++ b/kernel/livepatch/patch.c
@@ -50,7 +50,7 @@ static void notrace klp_ftrace_handler(unsigned long ip,
ops = container_of(fops, struct klp_ops, fops);

bit = ftrace_test_recursion_trylock();
- if (bit < 0)
+ if (WARN_ON_ONCE(bit < 0))
return;
/*
* A variant of synchronize_rcu() is used to allow patching functions
--
2.28.0

2020-11-06 10:10:04

by Miroslav Benes

Subject: Re: [PATCH 07/11 v3] livepatch: Trigger WARNING if livepatch function fails due to recursion

On Thu, 5 Nov 2020, Steven Rostedt wrote:

> From: "Steven Rostedt (VMware)" <[email protected]>
>
> If for some reason a function is called that triggers the recursion
> detection of live patching, trigger a warning. By not executing the live
> patch code, it is possible that the old unpatched function will be called
> placing the system into an unknown state.
>
> Link: https://lore.kernel.org/r/20201029145709.GD16774@alley
>
> Cc: Josh Poimboeuf <[email protected]>
> Cc: Jiri Kosina <[email protected]>
> Cc: Joe Lawrence <[email protected]>
> Cc: [email protected]
> Suggested-by: Miroslav Benes <[email protected]>
> Reviewed-by: Petr Mladek <[email protected]>
> Signed-off-by: Steven Rostedt (VMware) <[email protected]>

Acked-by: Miroslav Benes <[email protected]>

> ---
> Changes since v2:
>
> - Blame Miroslav instead of Petr ;-)

Thanks. Fortunately, if printk is broken in WARN_ON_ONCE(), I can always
blame Petr again :)

M