From mboxrd@z Thu Jan 1 00:00:00 1970 Received: from smtp.kernel.org (aws-us-west-2-korg-mail-1.web.codeaurora.org [10.30.226.201]) (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 18E3313C90B; Tue, 25 Jun 2024 10:01:29 +0000 (UTC) Authentication-Results: smtp.subspace.kernel.org; arc=none smtp.client-ip=10.30.226.201 ARC-Seal:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1719309689; cv=none; b=sGq1RcPj5ICzahTYBoaoR9cRNu3zgSrlk13PAb3hx7qUIVDxcoUcgUTiy+HeLG5F7qHTv+2UFzmRxGZquK7hgbIit/JsivtyYShC/CNSs69cW/nI8JbspQc4PPyPsNMzW8o1f0S+T1wRkoY2XVJYJr3CQpNy8lhrmHYRmWIWlTc= ARC-Message-Signature:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1719309689; c=relaxed/simple; bh=VhE8Vnqy+8hiiXaYtII6Rt3GK1ZumQJ96sDH6tG22Uk=; h=From:To:Cc:Subject:Date:Message-ID:In-Reply-To:References: MIME-Version; b=T21TZ3jYQPa7yeDH91G9/6osFeyQNkkDL5b0WmzAJOhLoRmCqZTgFJLAT6xZB3rm+DpbGDp+rvPpENNv3u+lHtNQpebHwukUJzzE7oC2DB2mwgVKrVMkN3srnGoE59K6pMRcn/sBPEKsHPlMp+Zi7AA5j/bhcUuPJ/xAEc+kx2o= ARC-Authentication-Results:i=1; smtp.subspace.kernel.org; dkim=pass (1024-bit key) header.d=linuxfoundation.org header.i=@linuxfoundation.org header.b=DlQVuBCx; arc=none smtp.client-ip=10.30.226.201 Authentication-Results: smtp.subspace.kernel.org; dkim=pass (1024-bit key) header.d=linuxfoundation.org header.i=@linuxfoundation.org header.b="DlQVuBCx" Received: by smtp.kernel.org (Postfix) with ESMTPSA id 89AB2C32781; Tue, 25 Jun 2024 10:01:28 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=linuxfoundation.org; s=korg; t=1719309688; bh=VhE8Vnqy+8hiiXaYtII6Rt3GK1ZumQJ96sDH6tG22Uk=; h=From:To:Cc:Subject:Date:In-Reply-To:References:From; b=DlQVuBCxoSlwvDPNbM81c++CYrlL5ktfeePZEJShqiY8y+/ipkol45BMTc51ofduH aQaslSlZ7EWqpYmdLYkFtkTuXZneG5iQHfvWWQVmU4gfT2ODkk/76hEJudmU4MbFk0 J7nkNiVHyOwdhKK7/IY8eVW74JRo7urdxLws9Fkk= From: Greg Kroah-Hartman To: stable@vger.kernel.org Cc: Greg Kroah-Hartman , patches@lists.linux.dev, Breno Leitao , Sean Christopherson Subject: [PATCH 6.1 099/131] KVM: Fix a data race on last_boosted_vcpu in kvm_vcpu_on_spin() Date: Tue, 25 Jun 2024 11:34:14 +0200 Message-ID: <20240625085529.702063242@linuxfoundation.org> X-Mailer: git-send-email 2.45.2 In-Reply-To: <20240625085525.931079317@linuxfoundation.org> References: <20240625085525.931079317@linuxfoundation.org> User-Agent: quilt/0.67 X-stable: review X-Patchwork-Hint: ignore Precedence: bulk X-Mailing-List: patches@lists.linux.dev List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 Content-Transfer-Encoding: 8bit 6.1-stable review patch. If anyone has any objections, please let me know. ------------------ From: Breno Leitao commit 49f683b41f28918df3e51ddc0d928cb2e934ccdb upstream. Use {READ,WRITE}_ONCE() to access kvm->last_boosted_vcpu to ensure the loads and stores are atomic. In the extremely unlikely scenario the compiler tears the stores, it's theoretically possible for KVM to attempt to get a vCPU using an out-of-bounds index, e.g. if the write is split into multiple 8-bit stores, and is paired with a 32-bit load on a VM with 257 vCPUs: CPU0 CPU1 last_boosted_vcpu = 0xff; (last_boosted_vcpu = 0x100) last_boosted_vcpu[15:8] = 0x01; i = (last_boosted_vcpu = 0x1ff) last_boosted_vcpu[7:0] = 0x00; vcpu = kvm->vcpu_array[0x1ff]; As detected by KCSAN: BUG: KCSAN: data-race in kvm_vcpu_on_spin [kvm] / kvm_vcpu_on_spin [kvm] write to 0xffffc90025a92344 of 4 bytes by task 4340 on cpu 16: kvm_vcpu_on_spin (arch/x86/kvm/../../../virt/kvm/kvm_main.c:4112) kvm handle_pause (arch/x86/kvm/vmx/vmx.c:5929) kvm_intel vmx_handle_exit (arch/x86/kvm/vmx/vmx.c:? arch/x86/kvm/vmx/vmx.c:6606) kvm_intel vcpu_run (arch/x86/kvm/x86.c:11107 arch/x86/kvm/x86.c:11211) kvm kvm_arch_vcpu_ioctl_run (arch/x86/kvm/x86.c:?) kvm kvm_vcpu_ioctl (arch/x86/kvm/../../../virt/kvm/kvm_main.c:?) kvm __se_sys_ioctl (fs/ioctl.c:52 fs/ioctl.c:904 fs/ioctl.c:890) __x64_sys_ioctl (fs/ioctl.c:890) x64_sys_call (arch/x86/entry/syscall_64.c:33) do_syscall_64 (arch/x86/entry/common.c:?) entry_SYSCALL_64_after_hwframe (arch/x86/entry/entry_64.S:130) read to 0xffffc90025a92344 of 4 bytes by task 4342 on cpu 4: kvm_vcpu_on_spin (arch/x86/kvm/../../../virt/kvm/kvm_main.c:4069) kvm handle_pause (arch/x86/kvm/vmx/vmx.c:5929) kvm_intel vmx_handle_exit (arch/x86/kvm/vmx/vmx.c:? arch/x86/kvm/vmx/vmx.c:6606) kvm_intel vcpu_run (arch/x86/kvm/x86.c:11107 arch/x86/kvm/x86.c:11211) kvm kvm_arch_vcpu_ioctl_run (arch/x86/kvm/x86.c:?) kvm kvm_vcpu_ioctl (arch/x86/kvm/../../../virt/kvm/kvm_main.c:?) kvm __se_sys_ioctl (fs/ioctl.c:52 fs/ioctl.c:904 fs/ioctl.c:890) __x64_sys_ioctl (fs/ioctl.c:890) x64_sys_call (arch/x86/entry/syscall_64.c:33) do_syscall_64 (arch/x86/entry/common.c:?) entry_SYSCALL_64_after_hwframe (arch/x86/entry/entry_64.S:130) value changed: 0x00000012 -> 0x00000000 Fixes: 217ece6129f2 ("KVM: use yield_to instead of sleep in kvm_vcpu_on_spin") Cc: stable@vger.kernel.org Signed-off-by: Breno Leitao Link: https://lore.kernel.org/r/20240510092353.2261824-1-leitao@debian.org Signed-off-by: Sean Christopherson Signed-off-by: Greg Kroah-Hartman --- virt/kvm/kvm_main.c | 5 +++-- 1 file changed, 3 insertions(+), 2 deletions(-) --- a/virt/kvm/kvm_main.c +++ b/virt/kvm/kvm_main.c @@ -3742,12 +3742,13 @@ void kvm_vcpu_on_spin(struct kvm_vcpu *m { struct kvm *kvm = me->kvm; struct kvm_vcpu *vcpu; - int last_boosted_vcpu = me->kvm->last_boosted_vcpu; + int last_boosted_vcpu; unsigned long i; int yielded = 0; int try = 3; int pass; + last_boosted_vcpu = READ_ONCE(kvm->last_boosted_vcpu); kvm_vcpu_set_in_spin_loop(me, true); /* * We boost the priority of a VCPU that is runnable but not @@ -3778,7 +3779,7 @@ void kvm_vcpu_on_spin(struct kvm_vcpu *m yielded = kvm_vcpu_yield_to(vcpu); if (yielded > 0) { - kvm->last_boosted_vcpu = i; + WRITE_ONCE(kvm->last_boosted_vcpu, i); break; } else if (yielded < 0) { try--;