Re: [PATCH v4 2/3] Revert "livepatch: Remove reliable stacktrace check in klp_try_switch_task()"

[Kamalesh Babulal]

On Tue, Jun 11, 2019 at 04:13:19PM +0200, Miroslav Benes wrote:
> This reverts commit 1d98a69e5cef3aeb68bcefab0e67e342d6bb4dad. Commit
> 31adf2308f33 ("livepatch: Convert error about unsupported reliable
> stacktrace into a warning") weakened the enforcement for architectures
> to have reliable stack traces support. The system only warns now about
> it.
> 
> It only makes sense to reintroduce the compile time checking in
> klp_try_switch_task() again and bail out early.
> 
> Signed-off-by: Miroslav Benes 

Reviewed-by: Kamalesh Babulal 

Re: [PATCH v4 2/3] Revert "livepatch: Remove reliable stacktrace check in klp_try_switch_task()"

[Petr Mladek]

On Tue 2019-06-11 16:13:19, Miroslav Benes wrote:
> This reverts commit 1d98a69e5cef3aeb68bcefab0e67e342d6bb4dad. Commit
> 31adf2308f33 ("livepatch: Convert error about unsupported reliable
> stacktrace into a warning") weakened the enforcement for architectures
> to have reliable stack traces support. The system only warns now about
> it.
> 
> It only makes sense to reintroduce the compile time checking in
> klp_try_switch_task() again and bail out early.
> 
> Signed-off-by: Miroslav Benes 

Reviewed-by: Petr Mladek 

Best Regards,
Petr

[PATCH v4 2/3] Revert "livepatch: Remove reliable stacktrace check in klp_try_switch_task()"

[Miroslav Benes]

This reverts commit 1d98a69e5cef3aeb68bcefab0e67e342d6bb4dad. Commit
31adf2308f33 ("livepatch: Convert error about unsupported reliable
stacktrace into a warning") weakened the enforcement for architectures
to have reliable stack traces support. The system only warns now about
it.

It only makes sense to reintroduce the compile time checking in
klp_try_switch_task() again and bail out early.

Signed-off-by: Miroslav Benes 
---
 kernel/livepatch/transition.c | 7 +++
 1 file changed, 7 insertions(+)

diff --git a/kernel/livepatch/transition.c b/kernel/livepatch/transition.c
index 8e8c79d4b204..7e7ef04689d1 100644
--- a/kernel/livepatch/transition.c
+++ b/kernel/livepatch/transition.c
@@ -293,6 +293,13 @@ static bool klp_try_switch_task(struct task_struct *task)
if (task->patch_state == klp_target_state)
return true;
 
+   /*
+* For arches which don't have reliable stack traces, we have to rely
+* on other methods (e.g., switching tasks at kernel exit).
+*/
+   if (!klp_have_reliable_stack())
+   return false;
+
/*
 * Now try to check the stack for any to-be-patched or to-be-unpatched
 * functions.  If all goes well, switch the task to the target patch
-- 
2.21.0