From mboxrd@z Thu Jan 1 00:00:00 1970 Received: from mail-pg1-f202.google.com (mail-pg1-f202.google.com [209.85.215.202]) (using TLSv1.2 with cipher ECDHE-RSA-AES128-GCM-SHA256 (128/128 bits)) (No client certificate requested) by smtp.subspace.kernel.org (Postfix) with ESMTPS id 3A09715B13A for ; Mon, 5 Aug 2024 16:26:12 +0000 (UTC) Authentication-Results: smtp.subspace.kernel.org; arc=none smtp.client-ip=209.85.215.202 ARC-Seal:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1722875173; cv=none; b=JYTq06I0DkyaxxhfXMXyUWKEoeMBfG8KN/UQKYzWX+bQB4q7TI2qVNozZbHvlW9zzB7DrMsV5A1hyPMfLJvR9bc1uyAEZadSElMOIf+Oa8F7tG88JLBWXZExzGO2DKCGo9zmTD49S2aw2fqgzAgGF9Cpa39PBV22AN4S27VBv4M= ARC-Message-Signature:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1722875173; c=relaxed/simple; bh=V7wy/IY78ADKe6MCQ9wGcOxH7LMu1vqwY8ggZZNETsw=; h=Date:In-Reply-To:Mime-Version:References:Message-ID:Subject:From: To:Cc:Content-Type; b=kBXa4kXHbzsx2xVXp6fJ5p4d8sqHNF+UD36V/aLSw8xxzOxHTLUYeXv/jqmIISAlREFrV2feGFtHsHS3pRVjSFcgnsp8YpPrdkbC1juZThSa2rl27gBGuiSejgN20AjfEEpr1oPwmUPYJsBXkFlKklDXykFLoz4vv35Q/Aesyi0= ARC-Authentication-Results:i=1; smtp.subspace.kernel.org; dmarc=pass (p=reject dis=none) header.from=google.com; spf=pass smtp.mailfrom=flex--seanjc.bounces.google.com; dkim=pass (2048-bit key) header.d=google.com header.i=@google.com header.b=qY6MB4L5; arc=none smtp.client-ip=209.85.215.202 Authentication-Results: smtp.subspace.kernel.org; dmarc=pass (p=reject dis=none) header.from=google.com Authentication-Results: smtp.subspace.kernel.org; spf=pass smtp.mailfrom=flex--seanjc.bounces.google.com Authentication-Results: smtp.subspace.kernel.org; dkim=pass (2048-bit key) header.d=google.com header.i=@google.com header.b="qY6MB4L5" Received: by mail-pg1-f202.google.com with SMTP id 41be03b00d2f7-7a1188b3bc2so8919897a12.2 for ; Mon, 05 Aug 2024 09:26:12 -0700 (PDT) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=google.com; s=20230601; t=1722875171; x=1723479971; darn=vger.kernel.org; h=cc:to:from:subject:message-id:references:mime-version:in-reply-to :date:from:to:cc:subject:date:message-id:reply-to; bh=LTrtRaPSzzv6povC2MZbVu/ikbGDz5GKGualsN8e2oo=; b=qY6MB4L5Lwi31rkl+bvZzaYqBl+XPnHuBcWu5CE/d5szt00UxkuBzG5B57wDEWIu3t LKHInBSXlHPHHBGu/pjLj7TcU7pxyqA6+Yzvt0ZyRdzli5o134jHG00eYiuRTbrS/egD ej9nZUtxAEv0zwPXH5nABT6eC99x2dTFkIiLfG7AS3OLOnEOzrFK/fVgbtmKve8jKmfJ rI68daVLPCdmtx84mBWJiXYGbImLInBKB+wf6zAfcEvuW+pykNoqAcq0TMX/ACvSEi9H zZxJHYXJFf3BUAz0PLu/u3WtF46zY63dmR/mU5+As4zbGHyIQ8PMHJYlsS5HT30kDbAj L5dw== X-Google-DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=1e100.net; s=20230601; t=1722875171; x=1723479971; h=cc:to:from:subject:message-id:references:mime-version:in-reply-to :date:x-gm-message-state:from:to:cc:subject:date:message-id:reply-to; bh=LTrtRaPSzzv6povC2MZbVu/ikbGDz5GKGualsN8e2oo=; b=ADsGvsUooxDf2nfAT5FnCeI3UEAg1hTriFuL0dYQiRrsRmxJSvimU4yCMO4T52iqIv SgzwztppNGmVUB2wmktNOg4pF2CwMgyOygAOXewrMgHbA8pRmLT8IK7PDt8KfNuSaTV/ aJBU4EyE6M7T3vgLraBacBLt4CEv6UEjvj+ytnTMlqV6b0WK2KOnaEzhtWK9D9/tTjjE YoDG6gdzIUmCVx2Aw1H5j1GVaBTlKCHqDCthT6yrZMGhlOxSxGw7wRrcvx9rBT0e4K14 sncz8vcBJSTLhwyaPZh7vsxFO3htnUacSY8wpCgu2iamGHEp6DuX0pLIvK9PS+4UUNq5 NLnQ== X-Forwarded-Encrypted: i=1; AJvYcCWAyvOqdGW2p0SI4uQM5VDZyVzCGpFf5AVFW1GJ5iIql4m3N4i0QMhdO5P3XI7hiUcWCT3Ct+jors/PpDIL68tfP7z9 X-Gm-Message-State: AOJu0YzRT4Tut0aXFI+uzwMqHrZDnlM+Z6r2vQyNa9rVyOIaKoDg77tS aT69FWGADgKYX5FNZugj7kbSh9ac7x4tQdBT+gmQ5kH9Swbm+Cs5KmXFErkTaOMlhiap+EXGO90 74Q== X-Google-Smtp-Source: AGHT+IEw6cjRWnePzyF97nk0/YCd4IV9HttqCP5c4LXLKTNvkvgZNp5EEi3fIHSWkDuAjgZYuZu0HrMv3+A= X-Received: from zagreus.c.googlers.com ([fda3:e722:ac3:cc00:7f:e700:c0a8:5c37]) (user=seanjc job=sendgmr) by 2002:a63:3f41:0:b0:7a1:2fb5:3ff7 with SMTP id 41be03b00d2f7-7b7438b1dc8mr27331a12.0.1722875171415; Mon, 05 Aug 2024 09:26:11 -0700 (PDT) Date: Mon, 5 Aug 2024 09:26:04 -0700 In-Reply-To: Precedence: bulk X-Mailing-List: kvm@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: Mime-Version: 1.0 References: <20240802202941.344889-1-seanjc@google.com> <20240802202941.344889-2-seanjc@google.com> Message-ID: Subject: Re: [PATCH 1/2] KVM: x86: Make x2APIC ID 100% readonly From: Sean Christopherson To: Michal Luczaj Cc: Paolo Bonzini , kvm@vger.kernel.org, linux-kernel@vger.kernel.org, Haoyu Wu , syzbot+545f1326f405db4e1c3e@syzkaller.appspotmail.com Content-Type: text/plain; charset="us-ascii" On Sun, Aug 04, 2024, Michal Luczaj wrote: > On 8/2/24 22:29, Sean Christopherson wrote: > > [...] > > Making the x2APIC ID fully readonly fixes a WARN in KVM's optimized map > > calculation, which expects the LDR to align with the x2APIC ID. > > > > WARNING: CPU: 2 PID: 958 at arch/x86/kvm/lapic.c:331 kvm_recalculate_apic_map+0x609/0xa00 [kvm] > > CPU: 2 PID: 958 Comm: recalc_apic_map Not tainted 6.4.0-rc3-vanilla+ #35 > > Hardware name: QEMU Standard PC (i440FX + PIIX, 1996), BIOS Arch Linux 1.16.2-1-1 04/01/2014 > > RIP: 0010:kvm_recalculate_apic_map+0x609/0xa00 [kvm] > > Call Trace: > > > > kvm_apic_set_state+0x1cf/0x5b0 [kvm] > > kvm_arch_vcpu_ioctl+0x1806/0x2100 [kvm] > > kvm_vcpu_ioctl+0x663/0x8a0 [kvm] > > __x64_sys_ioctl+0xb8/0xf0 > > do_syscall_64+0x56/0x80 > > entry_SYSCALL_64_after_hwframe+0x46/0xb0 > > RIP: 0033:0x7fade8b9dd6f > > Isn't this WARN_ON_ONCE() inherently racy, though? With your patch applied, > it can still be hit by juggling the APIC modes. Doh, right, the logic is unfortunately cross-vCPU. The sanity check could be conditioned on the APIC belonging to the running/loaded vCPU, but I'm leaning towards deleting it entirely. Though it did detect the KVM_SET_LAPIC backdoor... Anyone have a preference, or better idea? diff --git a/arch/x86/kvm/lapic.c b/arch/x86/kvm/lapic.c index a7172ba59ad2..67a0c116ebc0 100644 --- a/arch/x86/kvm/lapic.c +++ b/arch/x86/kvm/lapic.c @@ -352,7 +352,8 @@ static void kvm_recalculate_logical_map(struct kvm_apic_map *new, * additional work is required. */ if (apic_x2apic_mode(apic)) { - WARN_ON_ONCE(ldr != kvm_apic_calc_x2apic_ldr(kvm_x2apic_id(apic))); + WARN_ON_ONCE(ldr != kvm_apic_calc_x2apic_ldr(kvm_x2apic_id(apic)) && + vcpu == kvm_get_running_vcpu()); return; }