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[86.49.65.192]) by smtp.gmail.com with ESMTPSA id a1sm1557208edk.52.2020.11.11.15.46.09 (version=TLS1_3 cipher=TLS_AES_256_GCM_SHA384 bits=256/256); Wed, 11 Nov 2020 15:46:09 -0800 (PST) Date: Thu, 12 Nov 2020 00:46:06 +0100 From: Zdenek Kaspar To: Ben Gardon Cc: linux-kernel@vger.kernel.org, kvm@vger.kernel.org, Paolo Bonzini , Sean Christopherson , Peter Shier , Jim Mattson Subject: Re: [PATCH] kvm: x86/mmu: Fix is_tdp_mmu_check when using PAE Message-ID: <20201112004606.48c339a6.zkaspar82@gmail.com> In-Reply-To: <20201111185337.1237383-1-bgardon@google.com> References: <20201111185337.1237383-1-bgardon@google.com> MIME-Version: 1.0 Content-Type: text/plain; charset=US-ASCII Content-Transfer-Encoding: 7bit Precedence: bulk List-ID: X-Mailing-List: kvm@vger.kernel.org On Wed, 11 Nov 2020 10:53:37 -0800 Ben Gardon wrote: > When PAE is in use, the root_hpa will not have a shadow page > assoicated with it. In this case the kernel will crash with a NULL > pointer dereference. Add checks to ensure is_tdp_mmu_root works as > intended even when using PAE. > > Tested: compiles > > Fixes: 02c00b3a2f7e ("kvm: x86/mmu: Allocate and free TDP MMU roots") > Reported-by: Zdenek Kaspar > Signed-off-by: Ben Gardon > --- > arch/x86/kvm/mmu/tdp_mmu.c | 10 ++++++++++ > 1 file changed, 10 insertions(+) > > diff --git a/arch/x86/kvm/mmu/tdp_mmu.c b/arch/x86/kvm/mmu/tdp_mmu.c > index 27e381c9da6c..13013f4d98ad 100644 > --- a/arch/x86/kvm/mmu/tdp_mmu.c > +++ b/arch/x86/kvm/mmu/tdp_mmu.c > @@ -49,8 +49,18 @@ bool is_tdp_mmu_root(struct kvm *kvm, hpa_t hpa) > { > struct kvm_mmu_page *sp; > > + if (WARN_ON(!VALID_PAGE(hpa))) > + return false; > + > sp = to_shadow_page(hpa); > > + /* > + * If this VM is being run with PAE, the TDP MMU will not be > enabled > + * and the root HPA will not have a shadow page associated > with it. > + */ > + if (!sp) > + return false; > + > return sp->tdp_mmu_page && sp->root_count; > } > Fixes is_tdp_mmu_root NULL pointer dereference Tested on: Intel(R) Core(TM)2 CPU 6600 @ 2.40GHz Tested-by: Zdenek Kaspar