linux-kernel - Re: [PATCH v3 01/28] module: Extend the preempt disabled section in dereference_symbol

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Message-ID: <6e8ef32e-6698-496e-a9e4-09f0ade5f264@gmx.de>
Date: Wed, 8 Jan 2025 10:55:04 +0100
From: Helge Deller <deller@....de>
To: Sebastian Andrzej Siewior <bigeasy@...utronix.de>,
 linux-modules@...r.kernel.org, linux-kernel@...r.kernel.org
Cc: Daniel Gomez <da.gomez@...sung.com>, Luis Chamberlain
 <mcgrof@...nel.org>, "Paul E . McKenney" <paulmck@...nel.org>,
 Peter Zijlstra <peterz@...radead.org>, Petr Pavlu <petr.pavlu@...e.com>,
 Sami Tolvanen <samitolvanen@...gle.com>, Thomas Gleixner
 <tglx@...utronix.de>,
 "James E.J. Bottomley" <James.Bottomley@...senPartnership.com>,
 Christophe Leroy <christophe.leroy@...roup.eu>,
 Madhavan Srinivasan <maddy@...ux.ibm.com>,
 Michael Ellerman <mpe@...erman.id.au>, Naveen N Rao <naveen@...nel.org>,
 Nicholas Piggin <npiggin@...il.com>,
 Sergey Senozhatsky <sergey.senozhatsky.work@...il.com>,
 linux-parisc@...r.kernel.org, linuxppc-dev@...ts.ozlabs.org,
 Sergey Senozhatsky <senozhatsky@...omium.org>
Subject: Re: [PATCH v3 01/28] module: Extend the preempt disabled section in
 dereference_symbol_descriptor().

On 1/8/25 10:04, 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@...senPartnership.com>
> Cc: Christophe Leroy <christophe.leroy@...roup.eu>
> Cc: Helge Deller <deller@....de>
> Cc: Madhavan Srinivasan <maddy@...ux.ibm.com>
> Cc: Michael Ellerman <mpe@...erman.id.au>
> Cc: Naveen N Rao <naveen@...nel.org>
> Cc: Nicholas Piggin <npiggin@...il.com>
> Cc: Sergey Senozhatsky <sergey.senozhatsky.work@...il.com>
> Cc: linux-parisc@...r.kernel.org
> Cc: linuxppc-dev@...ts.ozlabs.org
> Reviewed-by: Sergey Senozhatsky <senozhatsky@...omium.org>
> Acked-by: Peter Zijlstra (Intel) <peterz@...radead.org>
> Signed-off-by: Sebastian Andrzej Siewior <bigeasy@...utronix.de>

Nice catch.

Acked-by: Helge Deller <deller@....de>

This patch really should be backported.
Can you add a Cc: stable tag?

Helge

> ---
>   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;
>   }