From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: X-Spam-Checker-Version: SpamAssassin 3.4.0 (2014-02-07) on aws-us-west-2-korg-lkml-1.web.codeaurora.org X-Spam-Level: X-Spam-Status: No, score=-9.8 required=3.0 tests=BAYES_00,DKIM_SIGNED, DKIM_VALID,DKIM_VALID_AU,FREEMAIL_FORGED_FROMDOMAIN,FREEMAIL_FROM, HEADER_FROM_DIFFERENT_DOMAINS,HK_RANDOM_FROM,INCLUDES_PATCH, MAILING_LIST_MULTI,SPF_HELO_NONE,SPF_PASS,USER_AGENT_GIT autolearn=ham autolearn_force=no version=3.4.0 Received: from mail.kernel.org (mail.kernel.org [198.145.29.99]) by smtp.lore.kernel.org (Postfix) with ESMTP id 372D4C433DB for ; Fri, 12 Mar 2021 08:32:37 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by mail.kernel.org (Postfix) with ESMTP id E780564FB3 for ; Fri, 12 Mar 2021 08:32:36 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S232274AbhCLIcC (ORCPT ); Fri, 12 Mar 2021 03:32:02 -0500 Received: from lindbergh.monkeyblade.net ([23.128.96.19]:38122 "EHLO lindbergh.monkeyblade.net" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S231764AbhCLIcC (ORCPT ); Fri, 12 Mar 2021 03:32:02 -0500 Received: from mail-pj1-x1031.google.com (mail-pj1-x1031.google.com [IPv6:2607:f8b0:4864:20::1031]) by lindbergh.monkeyblade.net (Postfix) with ESMTPS id D9250C061574 for ; Fri, 12 Mar 2021 00:32:01 -0800 (PST) Received: by mail-pj1-x1031.google.com with SMTP id mz6-20020a17090b3786b02900c16cb41d63so10730362pjb.2 for ; Fri, 12 Mar 2021 00:32:01 -0800 (PST) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=gmail.com; s=20161025; h=from:to:cc:subject:date:message-id:mime-version :content-transfer-encoding; bh=CXpW0jwlizj8GYTWHzwU8bAHHZKAdwaecc1NswSz/OE=; b=Ccj25YDTPKU/57oEL/GyBbzdoG3Cad1MC5quVjSh1ZoLeLYp/oRlBjJJWGKN2QAFlP 8299qZp3bQJMvvbvg1UTV+zydy/b2Hzgexu50JBiylyqKEq46bc3pxUCPDFH3O36/LFX kJ+br9H0Eb+q7AWaSuzrLYEOlgZTmA5nHPPYPoRt2LjDcOCsvEhsiwDSpQOONFpBj6Go lJyzEU4SzgXRLk2vkkV6B0KiscdvSAgwj+n3cN2FQBeBE4YQHa/XEJpZ1m7pXyy5owU2 fc+DgjWfaINp1NjLkCk0FcGg5htcxCPhikvIYN9Plw+biynveEp+496yv3vFkoYHUetv h+kA== X-Google-DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=1e100.net; s=20161025; h=x-gm-message-state:from:to:cc:subject:date:message-id:mime-version :content-transfer-encoding; bh=CXpW0jwlizj8GYTWHzwU8bAHHZKAdwaecc1NswSz/OE=; b=nQQMPoO+mKl8QDA2Rp+sTebfGaDdU/aUsZ2n7IqL6PYITbDRlaff+fNwiROoZ9wJYs Njza0wHrzo39bIZ0VV4eNKc5dbQf6NZkZ34xH45+JSBhRIoEC3KNpOvbg/aLQshBRx5m 24jp6zyMgjQd1kaiQSKll4wRl5Ef5aXFqWcR+GF/G7QocgKNrNHS0q+nXeDd6Gk257Qd eQ6rQHq1FKzc41G+D0D5mhcC3e4pDi3yJ9QNQGn0QBeAluUSRPYpUmRKhTUwA0442PQV jd2ISV5gBHzs6eNGt28MHPY15iF41l5dsskgNkyFhRtuv7W7PtRfGt/lHkfiClFpZ/W+ Txdg== X-Gm-Message-State: AOAM531mTeWJpx3S7ciDe3xPEKbWrVwvpLK/YFTOzbyTXIzRi5q0/iMZ PpE5opFOSSLekm75biyMxuI= X-Google-Smtp-Source: ABdhPJwP36IB34Owww3eDhkOSn0CtURJiGKPlguqyhIT5PdyQT3VFZJB4jFJR0/0jvVLyHI542wg2A== X-Received: by 2002:a17:90a:c389:: with SMTP id h9mr13158014pjt.226.1615537921339; Fri, 12 Mar 2021 00:32:01 -0800 (PST) Received: from localhost (176.222.229.35.bc.googleusercontent.com. [35.229.222.176]) by smtp.gmail.com with ESMTPSA id c25sm4340198pfo.101.2021.03.12.00.31.59 (version=TLS1_3 cipher=TLS_AES_256_GCM_SHA384 bits=256/256); Fri, 12 Mar 2021 00:32:00 -0800 (PST) From: Yuan Yao To: pbonzini@redhat.com, kvm@vger.kernel.org Cc: Yuan Yao Subject: [PATCH 1/1] Fix potential bitmap corruption in ksm_msr_allowed() Date: Fri, 12 Mar 2021 16:31:57 +0800 Message-Id: <20210312083157.25403-1-yaoyuan0329os@gmail.com> X-Mailer: git-send-email 2.30.1 MIME-Version: 1.0 Content-Transfer-Encoding: 8bit Precedence: bulk List-ID: X-Mailing-List: kvm@vger.kernel.org In ksm_msr_allowed() we read "count" out of the SRCU read section, this may cause access to corrupted bitmap in ksm_msr_allowed() due to kfree() by kvm_clear_msr_filter() in very small ratio. We can fix this by reading "count" value in the SRCU read section. The big comment block below shows detail of this issue: ===== Details ===== bool kvm_msr_allowed(struct kvm_vcpu *vcpu, u32 index, u32 type) { struct kvm *kvm = vcpu->kvm; struct msr_bitmap_range *ranges = kvm->arch.msr_filter.ranges; u32 count = kvm->arch.msr_filter.count; /* Schedule out happenes at this point, but before the kvm_clear_msr_filter() run "kvm->arch.msr_filter.count = 0;" on another CPU, so we get the "old" count value which should be > 0 if QEMU already set the MSR filter before. */ u32 i; bool r = kvm->arch.msr_filter.default_allow; int idx; /* MSR filtering not set up or x2APIC enabled, allow everything */ if (!count || (index >= 0x800 && index <= 0x8ff)) return true; /* Schedule in at this point later, now it has very small ratio that the kvm_clear_msr_filter() run on another CPU is doing "kfree(ranges[i].bitmap)" due to no exist srcu read sections of kvm->srcu, then the below code will access to a currupted(kfreed) bitmap, we already got count > 0 before. */ /* Prevent collision with set_msr_filter */ idx = srcu_read_lock(&kvm->srcu); for (i = 0; i < count; i++) { u32 start = ranges[i].base; u32 end = start + ranges[i].nmsrs; u32 flags = ranges[i].flags; unsigned long *bitmap = ranges[i].bitmap; if ((index >= start) && (index < end) && (flags & type)) { r = !!test_bit(index - start, bitmap); break; } } srcu_read_unlock(&kvm->srcu, idx); return r; } --- arch/x86/kvm/x86.c | 8 ++++++-- 1 file changed, 6 insertions(+), 2 deletions(-) diff --git a/arch/x86/kvm/x86.c b/arch/x86/kvm/x86.c index 46b0e52671bb..d6bc1b858167 100644 --- a/arch/x86/kvm/x86.c +++ b/arch/x86/kvm/x86.c @@ -1528,18 +1528,22 @@ bool kvm_msr_allowed(struct kvm_vcpu *vcpu, u32 index, u32 type) { struct kvm *kvm = vcpu->kvm; struct msr_bitmap_range *ranges = kvm->arch.msr_filter.ranges; - u32 count = kvm->arch.msr_filter.count; + u32 count; u32 i; bool r = kvm->arch.msr_filter.default_allow; int idx; /* MSR filtering not set up or x2APIC enabled, allow everything */ - if (!count || (index >= 0x800 && index <= 0x8ff)) + if (index >= 0x800 && index <= 0x8ff) return true; /* Prevent collision with set_msr_filter */ idx = srcu_read_lock(&kvm->srcu); + count = kvm->arch.msr_filter.count; + if (!count) + r = true; + for (i = 0; i < count; i++) { u32 start = ranges[i].base; u32 end = start + ranges[i].nmsrs; -- 2.30.1