linux-kernel - Re: [PATCH] [PATCH v3] perf/x86/amd: check event before enable to avoid GPF

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Message-ID: <20251014083748.GP3245006@noisy.programming.kicks-ass.net>
Date: Tue, 14 Oct 2025 10:37:48 +0200
From: Peter Zijlstra <peterz@...radead.org>
To: George Kennedy <george.kennedy@...cle.com>
Cc: ravi.bangoria@....com, harshit.m.mogalapalli@...cle.com,
	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,
	dongli.zhang@...cle.com, stable@...r.kernel.org
Subject: Re: [PATCH] [PATCH v3] perf/x86/amd: check event before enable to
 avoid GPF

On Tue, Oct 08, 2024 at 08:00:53AM -0500, George Kennedy wrote:
> On AMD machines cpuc->events[idx] can become NULL in a subtle race
> condition with NMI->throttle->x86_pmu_stop().
> 
> 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.
> 
> INFO: NMI handler (perf_event_nmi_handler) took too long to run: 13.143
>     msecs
> Oops: general protection fault, probably for non-canonical address
>     0xdffffc0000000034: 0000  PREEMPT SMP KASAN NOPTI
> KASAN: null-ptr-deref in range [0x00000000000001a0-0x00000000000001a7]
> CPU: 0 UID: 0 PID: 328415 Comm: repro_36674776 Not tainted 6.12.0-rc1-syzk
> RIP: 0010:x86_pmu_enable_event (arch/x86/events/perf_event.h:1195
>     arch/x86/events/core.c:1430)
> RSP: 0018:ffff888118009d60 EFLAGS: 00010012
> RAX: dffffc0000000000 RBX: 0000000000000000 RCX: 0000000000000000
> RDX: 0000000000000034 RSI: 0000000000000000 RDI: 00000000000001a0
> RBP: 0000000000000001 R08: 0000000000000000 R09: 0000000000000000
> R10: 0000000000000000 R11: 0000000000000000 R12: 0000000000000002
> R13: ffff88811802a440 R14: ffff88811802a240 R15: ffff8881132d8601
> FS:  00007f097dfaa700(0000) GS:ffff888118000000(0000) GS:0000000000000000
> CS:  0010 DS: 0000 ES: 0000 CR0: 0000000080050033
> CR2: 00000000200001c0 CR3: 0000000103d56000 CR4: 00000000000006f0
> Call Trace:
>  <IRQ>
> amd_pmu_enable_all (arch/x86/events/amd/core.c:760 (discriminator 2))
> x86_pmu_enable (arch/x86/events/core.c:1360)
> event_sched_out (kernel/events/core.c:1191 kernel/events/core.c:1186
>     kernel/events/core.c:2346)
> __perf_remove_from_context (kernel/events/core.c:2435)
> event_function (kernel/events/core.c:259)
> remote_function (kernel/events/core.c:92 (discriminator 1)
>     kernel/events/core.c:72 (discriminator 1))
> __flush_smp_call_function_queue (./arch/x86/include/asm/jump_label.h:27
>     ./include/linux/jump_label.h:207 ./include/trace/events/csd.h:64
>     kernel/smp.c:135 kernel/smp.c:540)
> __sysvec_call_function_single (./arch/x86/include/asm/jump_label.h:27
>     ./include/linux/jump_label.h:207
>     ./arch/x86/include/asm/trace/irq_vectors.h:99 arch/x86/kernel/smp.c:272)
> sysvec_call_function_single (arch/x86/kernel/smp.c:266 (discriminator 47)
>     arch/x86/kernel/smp.c:266 (discriminator 47))
>  </IRQ>
> 
> Reported-by: syzkaller <syzkaller@...glegroups.com>
> Signed-off-by: George Kennedy <george.kennedy@...cle.com>
> ---

Without a Fixes tag it goes into perf/core.