linux-kernel - Re: [PATCH] [PATCH v2] perf/x86/amd: check event before enable to avoid GPF

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Message-ID: <20251009071217.GB4067720@noisy.programming.kicks-ass.net>
Date: Thu, 9 Oct 2025 09:12:17 +0200
From: Peter Zijlstra <peterz@...radead.org>
To: Ravi Bangoria <ravi.bangoria@....com>
Cc: George Kennedy <george.kennedy@...cle.com>, mingo@...hat.com,
	harshit.m.mogalapalli@...cle.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
Subject: Re: [PATCH] [PATCH v2] perf/x86/amd: check event before enable to
 avoid GPF

On Mon, Oct 07, 2024 at 12:13:56PM +0530, Ravi Bangoria wrote:
> On 01-Oct-24 1:22 AM, 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>
> 
> Peter, Ingo,
> 
> I've been blocking this for quite some time without acting on it. Since
> the patch is trivial and harmless, I'm giving an Ack here. However, the
> underlying race condition is still unknown, so I will get back to it.
> 
> Acked-by: Ravi Bangoria <ravi.bangoria@....com>

Does this want a Fixes tag? If so, please reply to the v3 patch.