From mboxrd@z Thu Jan 1 00:00:00 1970 Received: from out-172.mta0.migadu.com (out-172.mta0.migadu.com [91.218.175.172]) (using TLSv1.2 with cipher ECDHE-RSA-AES256-GCM-SHA384 (256/256 bits)) (No client certificate requested) by smtp.subspace.kernel.org (Postfix) with ESMTPS id EF3621D5AC6 for ; Tue, 30 Sep 2025 08:52:59 +0000 (UTC) Authentication-Results: smtp.subspace.kernel.org; arc=none smtp.client-ip=91.218.175.172 ARC-Seal:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1759222381; cv=none; b=kYUEVyjQYvyw1+PfU3bi7mM6cEBgokJCeddD8DJdabBXLwFXKmZvTOFx8loe9AwJtJklPM+tnBEDoI295YRyY6kByqeVFjIPbZgSQa/jEocuKOo7j1XWQVjrXHm9iWS60BEtn7yBAVou+74qXZntt5St43qKZml0bhd0wGfvJqM= ARC-Message-Signature:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1759222381; c=relaxed/simple; bh=RolK84d4YEmZDJGqxxFUWjVWiZW2624dVKeGrayET1A=; h=From:To:Cc:Subject:Date:Message-Id:MIME-Version; b=HMXHKNUI5zq4g2uFgdypH7wh4q5nswIlCkeKsw+leiar9NMymKfqeju+vAjQyA4UFuJ0R2COdKDf/tz80qDoIqJpuLLaHMrCo+RLmBz9rD9DHx2C4tkgmcpf6Dozzlnfs+Ocg9q18V49pNx5XS6nvL2K6kozYC+nWL53bV8jEQE= ARC-Authentication-Results:i=1; smtp.subspace.kernel.org; dmarc=pass (p=none dis=none) header.from=linux.dev; spf=pass smtp.mailfrom=linux.dev; dkim=pass (1024-bit key) header.d=linux.dev header.i=@linux.dev header.b=C3gpJDXO; arc=none smtp.client-ip=91.218.175.172 Authentication-Results: smtp.subspace.kernel.org; dmarc=pass (p=none dis=none) header.from=linux.dev Authentication-Results: smtp.subspace.kernel.org; spf=pass smtp.mailfrom=linux.dev Authentication-Results: smtp.subspace.kernel.org; dkim=pass (1024-bit key) header.d=linux.dev header.i=@linux.dev header.b="C3gpJDXO" X-Report-Abuse: Please report any abuse attempt to abuse@migadu.com and include these headers. DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=linux.dev; s=key1; t=1759222367; h=from:from:reply-to:subject:subject:date:date:message-id:message-id: to:to:cc:cc:mime-version:mime-version: content-transfer-encoding:content-transfer-encoding; bh=fO4H831Gj0XcQXa/CBJ4KpYimoBucD9IAyXJi5ODctk=; b=C3gpJDXOACHAQEnoMAoBwnVQZs5KRLvQ4499eGhI1TEpqdUAotKSeTQQQ+7J5rLE/r9j0p U1EY9/gNKh1gWXuzn/tZB0FM/oN0wIeiFV97Q0M8NapuFHLOwDpz3/t6rsdToDRWgauqVr wGZlNgkLEtx+vb0xmF3F4J6v/7b29VE= From: Oliver Upton To: kvmarm@lists.linux.dev Cc: Marc Zyngier , Joey Gouly , Suzuki K Poulose , Zenghui Yu , Oliver Upton , stable@vger.kernel.org Subject: [PATCH] KVM: arm64: Prevent access to vCPU events before init Date: Tue, 30 Sep 2025 01:52:37 -0700 Message-Id: <20250930085237.108326-1-oliver.upton@linux.dev> Precedence: bulk X-Mailing-List: stable@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 Content-Transfer-Encoding: 8bit X-Migadu-Flow: FLOW_OUT Another day, another syzkaller bug. KVM erroneously allows userspace to pend vCPU events for a vCPU that hasn't been initialized yet, leading to KVM interpreting a bunch of uninitialized garbage for routing / injecting the exception. In one case the injection code and the hyp disagree on whether the vCPU has a 32bit EL1 and put the vCPU into an illegal mode for AArch64, tripping the BUG() in exception_target_el() during the next injection: kernel BUG at arch/arm64/kvm/inject_fault.c:40! Internal error: Oops - BUG: 00000000f2000800 [#1] SMP CPU: 3 UID: 0 PID: 318 Comm: repro Not tainted 6.17.0-rc4-00104-g10fd0285305d #6 PREEMPT Hardware name: linux,dummy-virt (DT) pstate: 21402009 (nzCv daif +PAN -UAO -TCO +DIT -SSBS BTYPE=--) pc : exception_target_el+0x88/0x8c lr : pend_serror_exception+0x18/0x13c sp : ffff800082f03a10 x29: ffff800082f03a10 x28: ffff0000cb132280 x27: 0000000000000000 x26: 0000000000000000 x25: ffff0000c2a99c20 x24: 0000000000000000 x23: 0000000000008000 x22: 0000000000000002 x21: 0000000000000004 x20: 0000000000008000 x19: ffff0000c2a99c20 x18: 0000000000000000 x17: 0000000000000000 x16: 0000000000000000 x15: 00000000200000c0 x14: 0000000000000000 x13: 0000000000000000 x12: 0000000000000000 x11: 0000000000000000 x10: 0000000000000000 x9 : 0000000000000000 x8 : ffff800082f03af8 x7 : 0000000000000000 x6 : 0000000000000000 x5 : ffff800080f621f0 x4 : 0000000000000000 x3 : 0000000000000000 x2 : 000000000040009b x1 : 0000000000000003 x0 : ffff0000c2a99c20 Call trace: exception_target_el+0x88/0x8c (P) kvm_inject_serror_esr+0x40/0x3b4 __kvm_arm_vcpu_set_events+0xf0/0x100 kvm_arch_vcpu_ioctl+0x180/0x9d4 kvm_vcpu_ioctl+0x60c/0x9f4 __arm64_sys_ioctl+0xac/0x104 invoke_syscall+0x48/0x110 el0_svc_common.constprop.0+0x40/0xe0 do_el0_svc+0x1c/0x28 el0_svc+0x34/0xf0 el0t_64_sync_handler+0xa0/0xe4 el0t_64_sync+0x198/0x19c Code: f946bc01 b4fffe61 9101e020 17fffff2 (d4210000) Reject the ioctls outright as no sane VMM would call these before KVM_ARM_VCPU_INIT anyway. Even if it did the exception would've been thrown away by the eventual reset of the vCPU's state. Cc: stable@vger.kernel.org # 6.17 Fixes: b7b27facc7b5 ("arm/arm64: KVM: Add KVM_GET/SET_VCPU_EVENTS") Signed-off-by: Oliver Upton --- While the blamed commit is indeed broken, only 6.17+ kernels actually hit the BUG() due to commit efa1368ba9f4 ("KVM: arm64: Commit exceptions from KVM_SET_VCPU_EVENTS immediately). arch/arm64/kvm/arm.c | 6 ++++++ 1 file changed, 6 insertions(+) diff --git a/arch/arm64/kvm/arm.c b/arch/arm64/kvm/arm.c index a59b4046617c..c44357d26ee8 100644 --- a/arch/arm64/kvm/arm.c +++ b/arch/arm64/kvm/arm.c @@ -1795,6 +1795,9 @@ long kvm_arch_vcpu_ioctl(struct file *filp, case KVM_GET_VCPU_EVENTS: { struct kvm_vcpu_events events; + if (!kvm_vcpu_initialized(vcpu)) + return -ENOEXEC; + if (kvm_arm_vcpu_get_events(vcpu, &events)) return -EINVAL; @@ -1806,6 +1809,9 @@ long kvm_arch_vcpu_ioctl(struct file *filp, case KVM_SET_VCPU_EVENTS: { struct kvm_vcpu_events events; + if (!kvm_vcpu_initialized(vcpu)) + return -ENOEXEC; + if (copy_from_user(&events, argp, sizeof(events))) return -EFAULT; base-commit: 10fd0285305d0b48e8a3bf15d4f17fc4f3d68cb6 -- 2.39.5