linux-kernel - [tip: perf/core] perf/x86/amd: Check event before enable to avoid GPF

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Message-ID: <176060719457.709179.10142302566518648596.tip-bot2@tip-bot2>
Date: Thu, 16 Oct 2025 09:33:14 -0000
From: "tip-bot2 for George Kennedy" <tip-bot2@...utronix.de>
To: linux-tip-commits@...r.kernel.org
Cc: syzkaller <syzkaller@...glegroups.com>,
 George Kennedy <george.kennedy@...cle.com>,
 "Peter Zijlstra (Intel)" <peterz@...radead.org>, x86@...nel.org,
 linux-kernel@...r.kernel.org
Subject: [tip: perf/core] perf/x86/amd: Check event before enable to avoid GPF

The following commit has been merged into the perf/core branch of tip:

Commit-ID:     866cf36bfee4fba6a492d2dcc5133f857e3446b0
Gitweb:        https://git.kernel.org/tip/866cf36bfee4fba6a492d2dcc5133f857e3446b0
Author:        George Kennedy <george.kennedy@...cle.com>
AuthorDate:    Tue, 08 Oct 2024 08:00:53 -05:00
Committer:     Peter Zijlstra <peterz@...radead.org>
CommitterDate: Thu, 16 Oct 2025 11:13:47 +02:00

perf/x86/amd: Check event before enable to avoid GPF

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>
Signed-off-by: Peter Zijlstra (Intel) <peterz@...radead.org>
---
 arch/x86/events/amd/core.c | 7 ++++++-
 1 file changed, 6 insertions(+), 1 deletion(-)

diff --git a/arch/x86/events/amd/core.c b/arch/x86/events/amd/core.c
index b20661b..8868f5f 100644
--- a/arch/x86/events/amd/core.c
+++ b/arch/x86/events/amd/core.c
@@ -763,7 +763,12 @@ static void amd_pmu_enable_all(int added)
 		if (!test_bit(idx, cpuc->active_mask))
 			continue;
 
-		amd_pmu_enable_event(cpuc->events[idx]);
+		/*
+		 * FIXME: cpuc->events[idx] can become NULL in a subtle race
+		 * condition with NMI->throttle->x86_pmu_stop().
+		 */
+		if (cpuc->events[idx])
+			amd_pmu_enable_event(cpuc->events[idx]);
 	}
 }