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[91.219.240.2]) by smtp.gmail.com with ESMTPSA id l17sm6367416wmi.3.2020.05.26.00.33.28 (version=TLS1_3 cipher=TLS_AES_256_GCM_SHA384 bits=256/256); Tue, 26 May 2020 00:33:29 -0700 (PDT) From: Vitaly Kuznetsov To: John Hubbard , LKML Cc: Souptick Joarder , John Hubbard , Ingo Molnar , Borislav Petkov , Thomas Gleixner , Paolo Bonzini , Sean Christopherson , Wanpeng Li , Jim Mattson , Joerg Roedel , "H . Peter Anvin" , x86@kernel.org, kvm@vger.kernel.org Subject: Re: [PATCH 1/2] KVM: SVM: fix svn_pin_memory()'s use of get_user_pages_fast() In-Reply-To: <20200526062207.1360225-2-jhubbard@nvidia.com> References: <20200526062207.1360225-1-jhubbard@nvidia.com> <20200526062207.1360225-2-jhubbard@nvidia.com> Date: Tue, 26 May 2020 09:33:27 +0200 Message-ID: <87imgj6th4.fsf@vitty.brq.redhat.com> MIME-Version: 1.0 Content-Type: text/plain Sender: linux-kernel-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org John Hubbard writes: > There are two problems in svn_pin_memory(): > > 1) The return value of get_user_pages_fast() is stored in an > unsigned long, although the declared return value is of type int. > This will not cause any symptoms, but it is misleading. > Fix this by changing the type of npinned to "int". > > 2) The number of pages passed into get_user_pages_fast() is stored > in an unsigned long, even though get_user_pages_fast() accepts an > int. This means that it is possible to silently overflow the number > of pages. > > Fix this by adding a WARN_ON_ONCE() and an early error return. The > npages variable is left as an unsigned long for convenience in > checking for overflow. > > Fixes: 89c505809052 ("KVM: SVM: Add support for KVM_SEV_LAUNCH_UPDATE_DATA command") > Cc: Ingo Molnar > Cc: Borislav Petkov > Cc: Thomas Gleixner > Cc: Paolo Bonzini > Cc: Sean Christopherson > Cc: Vitaly Kuznetsov > Cc: Wanpeng Li > Cc: Jim Mattson > Cc: Joerg Roedel > Cc: H. Peter Anvin > Cc: x86@kernel.org > Cc: kvm@vger.kernel.org > Signed-off-by: John Hubbard > --- > arch/x86/kvm/svm/sev.c | 6 +++++- > 1 file changed, 5 insertions(+), 1 deletion(-) > > diff --git a/arch/x86/kvm/svm/sev.c b/arch/x86/kvm/svm/sev.c > index 89f7f3aebd31..9693db1af57c 100644 > --- a/arch/x86/kvm/svm/sev.c > +++ b/arch/x86/kvm/svm/sev.c > @@ -313,7 +313,8 @@ static struct page **sev_pin_memory(struct kvm *kvm, unsigned long uaddr, > int write) > { > struct kvm_sev_info *sev = &to_kvm_svm(kvm)->sev_info; > - unsigned long npages, npinned, size; > + unsigned long npages, size; > + int npinned; > unsigned long locked, lock_limit; > struct page **pages; > unsigned long first, last; > @@ -333,6 +334,9 @@ static struct page **sev_pin_memory(struct kvm *kvm, unsigned long uaddr, > return NULL; > } > > + if (WARN_ON_ONCE(npages > INT_MAX)) > + return NULL; > + I bit unrelated to this patch, but callers of sev_pin_memory() treat NULL differently: sev_launch_secret()/svm_register_enc_region() return -ENOMEM sev_dbg_crypt() returns -EFAULT Should we switch to ERR_PTR() to preserve the error? > /* Avoid using vmalloc for smaller buffers. */ > size = npages * sizeof(struct page *); > if (size > PAGE_SIZE) Reviewed-by: Vitaly Kuznetsov -- Vitaly