[PATCH v2 01/28] module: Extend the preempt disabled section in dereference_symbol_descriptor().

[PATCH v2 01/28] module: Extend the preempt disabled section in dereference_symbol_descriptor().

[Sebastian Andrzej Siewior]

dereference_symbol_descriptor() needs to obtain the module pointer
belonging to pointer in order to resolve that pointer.
The returned mod pointer is obtained under RCU-sched/ preempt_disable()
guarantees and needs to be used within this section to ensure that the
module is not removed in the meantime.

Extend the preempt_disable() section to also cover
dereference_module_function_descriptor().

Fixes: 04b8eb7a4ccd9 ("symbol lookup: introduce dereference_symbol_descriptor()")
Cc: "James E.J. Bottomley" <James.Bottomley@HansenPartnership.com>
Cc: Christophe Leroy <christophe.leroy@csgroup.eu>
Cc: Helge Deller <deller@gmx.de>
Cc: Madhavan Srinivasan <maddy@linux.ibm.com>
Cc: Michael Ellerman <mpe@ellerman.id.au>
Cc: Naveen N Rao <naveen@kernel.org>
Cc: Nicholas Piggin <npiggin@gmail.com>
Cc: Sergey Senozhatsky <sergey.senozhatsky.work@gmail.com>
Cc: linux-parisc@vger.kernel.org
Cc: linuxppc-dev@lists.ozlabs.org
Signed-off-by: Sebastian Andrzej Siewior <bigeasy@linutronix.de>
---
 include/linux/kallsyms.h | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/include/linux/kallsyms.h b/include/linux/kallsyms.h
index c3f075e8f60cb..1c6a6c1704d8d 100644
--- a/include/linux/kallsyms.h
+++ b/include/linux/kallsyms.h
@@ -57,10 +57,10 @@ static inline void *dereference_symbol_descriptor(void *ptr)
 
 	preempt_disable();
 	mod = __module_address((unsigned long)ptr);
-	preempt_enable();
 
 	if (mod)
 		ptr = dereference_module_function_descriptor(mod, ptr);
+	preempt_enable();
 #endif
 	return ptr;
 }
-- 
2.45.2

Re: [PATCH v2 01/28] module: Extend the preempt disabled section in dereference_symbol_descriptor().

[Sergey Senozhatsky]

On (24/12/20 18:41), Sebastian Andrzej Siewior wrote:
> dereference_symbol_descriptor() needs to obtain the module pointer
> belonging to pointer in order to resolve that pointer.
> The returned mod pointer is obtained under RCU-sched/ preempt_disable()
> guarantees and needs to be used within this section to ensure that the
> module is not removed in the meantime.
> 
> Extend the preempt_disable() section to also cover
> dereference_module_function_descriptor().
> 
> Fixes: 04b8eb7a4ccd9 ("symbol lookup: introduce dereference_symbol_descriptor()")
> Cc: "James E.J. Bottomley" <James.Bottomley@HansenPartnership.com>
> Cc: Christophe Leroy <christophe.leroy@csgroup.eu>
> Cc: Helge Deller <deller@gmx.de>
> Cc: Madhavan Srinivasan <maddy@linux.ibm.com>
> Cc: Michael Ellerman <mpe@ellerman.id.au>
> Cc: Naveen N Rao <naveen@kernel.org>
> Cc: Nicholas Piggin <npiggin@gmail.com>
> Cc: Sergey Senozhatsky <sergey.senozhatsky.work@gmail.com>
> Cc: linux-parisc@vger.kernel.org
> Cc: linuxppc-dev@lists.ozlabs.org
> Signed-off-by: Sebastian Andrzej Siewior <bigeasy@linutronix.de>

FWIW
Reviewed-by: Sergey Senozhatsky <senozhatsky@chromium.org>