linux-kernel - Re: [PATCH] perf/x86/amd: check event before enable to avoid GPF

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Date: Thu, 30 May 2024 09:07:30 +0530
From: Ravi Bangoria <ravi.bangoria@....com>
To: George Kennedy <george.kennedy@...cle.com>
Cc: harshit.m.mogalapalli@...cle.com, peterz@...radead.org, mingo@...hat.com,
 acme@...nel.org, namhyung@...nel.org, mark.rutland@....com,
 alexander.shishkin@...ux.intel.com, jolsa@...nel.org, irogers@...gle.com,
 adrian.hunter@...el.com, kan.liang@...ux.intel.com, tglx@...utronix.de,
 bp@...en8.de, dave.hansen@...ux.intel.com, x86@...nel.org, hpa@...or.com,
 linux-perf-users@...r.kernel.org, linux-kernel@...r.kernel.org,
 ravi.bangoria@....com
Subject: Re: [PATCH] perf/x86/amd: check event before enable to avoid GPF

Hi George,

> Events can be deleted and the entry can be NULL.

Can you please also explain "how".

> Check event for NULL in amd_pmu_enable_all() before enable to avoid a GPF.
> This appears to be an AMD only issue.
> 
> Syzkaller reported a GPF in amd_pmu_enable_all.

Can you please provide a bug report link? Also, any reproducer?

> @@ -760,7 +760,8 @@ static void amd_pmu_enable_all(int added)
>  		if (!test_bit(idx, cpuc->active_mask))
>  			continue;
>  
> -		amd_pmu_enable_event(cpuc->events[idx]);
> +		if (cpuc->events[idx])
> +			amd_pmu_enable_event(cpuc->events[idx]);

What if cpuc->events[idx] becomes NULL after if (cpuc->events[idx]) but
before amd_pmu_enable_event(cpuc->events[idx])?

Thanks,
Ravi