linux-kernel - Re: [PATCH 1/3] perf_event: fix race in perf_swevent_get_recursion

lists.openwall.net		lists / announce owl-users owl-dev john-users john-dev passwdqc-users yescrypt popa3d-users / oss-security kernel-hardening musl sabotage tlsify passwords / crypt-dev xvendor / Bugtraq Full-Disclosure linux-kernel linux-netdev linux-ext4 linux-hardening linux-cve-announce PHC
Open Source and information security mailing list archives

Hash Suite: Windows password security audit tool. GUI, reports in PDF.

[<prev] [next>] [<thread-prev] [thread-next>] [day] [month] [year] [list]

Message-ID: <20100118164128.GI10364@nowhere>
Date:	Mon, 18 Jan 2010 17:41:30 +0100
From:	Frederic Weisbecker <fweisbec@...il.com>
To:	Xiao Guangrong <xiaoguangrong@...fujitsu.com>
Cc:	Ingo Molnar <mingo@...e.hu>, Peter Zijlstra <peterz@...radead.org>,
	Paul Mackerras <paulus@...ba.org>,
	LKML <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH 1/3] perf_event: fix race in
	perf_swevent_get_recursion_context()

On Mon, Jan 18, 2010 at 09:42:34PM +0800, Xiao Guangrong wrote:
> It only disable preemption in perf_swevent_get_recursion_context()
> it can't avoid race of hard-irq and NMI
> 
> In this patch, we use atomic operation to avoid it and reduce
> cpu_ctx->recursion size, it also make this patch no need diable
> preemption
> 
> Signed-off-by: Xiao Guangrong <xiaoguangrong@...fujitsu.com>



I don't understand what is racy in what we have currently.



>  int perf_swevent_get_recursion_context(void)
>  {
> -	struct perf_cpu_context *cpuctx = &get_cpu_var(perf_cpu_context);
> +	struct perf_cpu_context *cpuctx = &__get_cpu_var(perf_cpu_context);
>  	int rctx;
>  
>  	if (in_nmi())
> @@ -3933,13 +3933,8 @@ int perf_swevent_get_recursion_context(void)
>  	else
>  		rctx = 0;
>  
> -	if (cpuctx->recursion[rctx]) {
> -		put_cpu_var(perf_cpu_context);
> +	if (test_and_set_bit(rctx, &cpuctx->recursion))
>  		return -1;



This looks broken. We don't call back perf_swevent_put_recursion_context
in fail case, so the bit won't ever be cleared once we recurse.

--
To unsubscribe from this list: send the line "unsubscribe linux-kernel" in
the body of a message to majordomo@...r.kernel.org
More majordomo info at  http://vger.kernel.org/majordomo-info.html
Please read the FAQ at  http://www.tux.org/lkml/