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[35.247.111.240]) by smtp.gmail.com with ESMTPSA id g8sm9749944pfo.85.2021.05.03.13.53.12 (version=TLS1_3 cipher=TLS_AES_256_GCM_SHA384 bits=256/256); Mon, 03 May 2021 13:53:12 -0700 (PDT) Date: Mon, 3 May 2021 20:53:09 +0000 From: Sean Christopherson To: Siddharth Chandrasekaran Cc: Paolo Bonzini , Vitaly Kuznetsov , Wanpeng Li , Jim Mattson , Joerg Roedel , Thomas Gleixner , Ingo Molnar , Borislav Petkov , x86@kernel.org, "H. Peter Anvin" , kvm@vger.kernel.org, linux-kernel@vger.kernel.org Subject: Re: [PATCH] KVM: x86: Hoist input checks in kvm_add_msr_filter() Message-ID: References: <20210503122111.13775-1-sidcha@amazon.de> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20210503122111.13775-1-sidcha@amazon.de> Precedence: bulk List-ID: X-Mailing-List: kvm@vger.kernel.org On Mon, May 03, 2021, Siddharth Chandrasekaran wrote: > In ioctl KVM_X86_SET_MSR_FILTER, input from user space is validated > after a memdup_user(). For invalid inputs we'd memdup and then call > kfree unnecessarily. Hoist input validation to avoid kfree altogether. > > Signed-off-by: Siddharth Chandrasekaran > --- > arch/x86/kvm/x86.c | 21 ++++++--------------- > 1 file changed, 6 insertions(+), 15 deletions(-) > > diff --git a/arch/x86/kvm/x86.c b/arch/x86/kvm/x86.c > index ee0dc58ac3a5..15c20b31cc91 100644 > --- a/arch/x86/kvm/x86.c > +++ b/arch/x86/kvm/x86.c > @@ -5393,11 +5393,16 @@ static int kvm_add_msr_filter(struct kvm_x86_msr_filter *msr_filter, > struct msr_bitmap_range range; > unsigned long *bitmap = NULL; > size_t bitmap_size; > - int r; > > if (!user_range->nmsrs) > return 0; > > + if (user_range->flags & ~(KVM_MSR_FILTER_READ | KVM_MSR_FILTER_WRITE)) > + return -EINVAL; > + > + if (!user_range->flags) > + return -EINVAL; > + > bitmap_size = BITS_TO_LONGS(user_range->nmsrs) * sizeof(long); > if (!bitmap_size || bitmap_size > KVM_MSR_FILTER_MAX_BITMAP_SIZE) > return -EINVAL; > @@ -5413,24 +5418,10 @@ static int kvm_add_msr_filter(struct kvm_x86_msr_filter *msr_filter, > .bitmap = bitmap, > }; > > - if (range.flags & ~(KVM_MSR_FILTER_READ | KVM_MSR_FILTER_WRITE)) { > - r = -EINVAL; > - goto err; > - } > - > - if (!range.flags) { > - r = -EINVAL; > - goto err; > - } > - > - /* Everything ok, add this range identifier. */ > msr_filter->ranges[msr_filter->count] = range; Might be worth elminating the intermediate "range", too. Doesn't affect output, but it would make it a little more obvious that the new range is mostly coming straight from userspace input. E.g. msr_filter->ranges[msr_filter->count] = (struct msr_bitmap_range) { .flags = user_range->flags, .base = user_range->base, .nmsrs = user_range->nmsrs, .bitmap = bitmap, }; Either way: Reviewed-by: Sean Christopherson > msr_filter->count++; > > return 0; > -err: > - kfree(bitmap); > - return r; > } > > static int kvm_vm_ioctl_set_msr_filter(struct kvm *kvm, void __user *argp) > --