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[2003:d8:2f15:6200:d485:1bcd:d708:f5df]) by smtp.gmail.com with ESMTPSA id ffacd0b85a97d-3a1f5a2d96csm20462242f8f.69.2025.05.14.10.39.22 (version=TLS1_3 cipher=TLS_AES_128_GCM_SHA256 bits=128/128); Wed, 14 May 2025 10:39:24 -0700 (PDT) Message-ID: Date: Wed, 14 May 2025 19:39:22 +0200 Precedence: bulk X-Mailing-List: linux-arm-msm@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 User-Agent: Mozilla Thunderbird Subject: Re: [PATCH v9 08/17] KVM: guest_memfd: Check that userspace_addr and fd+offset refer to same range To: Fuad Tabba , kvm@vger.kernel.org, linux-arm-msm@vger.kernel.org, linux-mm@kvack.org Cc: pbonzini@redhat.com, chenhuacai@kernel.org, mpe@ellerman.id.au, anup@brainfault.org, paul.walmsley@sifive.com, palmer@dabbelt.com, aou@eecs.berkeley.edu, seanjc@google.com, viro@zeniv.linux.org.uk, brauner@kernel.org, willy@infradead.org, akpm@linux-foundation.org, xiaoyao.li@intel.com, yilun.xu@intel.com, chao.p.peng@linux.intel.com, jarkko@kernel.org, amoorthy@google.com, dmatlack@google.com, isaku.yamahata@intel.com, mic@digikod.net, vbabka@suse.cz, vannapurve@google.com, ackerleytng@google.com, mail@maciej.szmigiero.name, michael.roth@amd.com, wei.w.wang@intel.com, liam.merwick@oracle.com, isaku.yamahata@gmail.com, kirill.shutemov@linux.intel.com, suzuki.poulose@arm.com, steven.price@arm.com, quic_eberman@quicinc.com, quic_mnalajal@quicinc.com, quic_tsoni@quicinc.com, quic_svaddagi@quicinc.com, quic_cvanscha@quicinc.com, quic_pderrin@quicinc.com, quic_pheragu@quicinc.com, catalin.marinas@arm.com, james.morse@arm.com, yuzenghui@huawei.com, oliver.upton@linux.dev, maz@kernel.org, will@kernel.org, qperret@google.com, keirf@google.com, roypat@amazon.co.uk, shuah@kernel.org, hch@infradead.org, jgg@nvidia.com, rientjes@google.com, jhubbard@nvidia.com, fvdl@google.com, hughd@google.com, jthoughton@google.com, peterx@redhat.com, pankaj.gupta@amd.com, ira.weiny@intel.com References: <20250513163438.3942405-1-tabba@google.com> <20250513163438.3942405-9-tabba@google.com> From: David Hildenbrand Content-Language: en-US Autocrypt: addr=david@redhat.com; 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charset=UTF-8; format=flowed Content-Transfer-Encoding: 7bit On 13.05.25 18:34, Fuad Tabba wrote: > From: Ackerley Tng > > On binding of a guest_memfd with a memslot, check that the slot's > userspace_addr and the requested fd and offset refer to the same memory > range. > > This check is best-effort: nothing prevents userspace from later mapping > other memory to the same provided in slot->userspace_addr and breaking > guest operation. > > Suggested-by: David Hildenbrand > Suggested-by: Sean Christopherson > Suggested-by: Yan Zhao > Signed-off-by: Ackerley Tng > Signed-off-by: Fuad Tabba > --- > virt/kvm/guest_memfd.c | 37 ++++++++++++++++++++++++++++++++++--- > 1 file changed, 34 insertions(+), 3 deletions(-) > > diff --git a/virt/kvm/guest_memfd.c b/virt/kvm/guest_memfd.c > index 8e6d1866b55e..2f499021df66 100644 > --- a/virt/kvm/guest_memfd.c > +++ b/virt/kvm/guest_memfd.c > @@ -556,6 +556,32 @@ int kvm_gmem_create(struct kvm *kvm, struct kvm_create_guest_memfd *args) > return __kvm_gmem_create(kvm, size, flags); > } > > +static bool kvm_gmem_is_same_range(struct kvm *kvm, > + struct kvm_memory_slot *slot, > + struct file *file, loff_t offset) > +{ > + struct mm_struct *mm = kvm->mm; > + loff_t userspace_addr_offset; > + struct vm_area_struct *vma; > + bool ret = false; > + > + mmap_read_lock(mm); > + > + vma = vma_lookup(mm, slot->userspace_addr); > + if (!vma) > + goto out; > + > + if (vma->vm_file != file) > + goto out; > + > + userspace_addr_offset = slot->userspace_addr - vma->vm_start; > + ret = userspace_addr_offset + (vma->vm_pgoff << PAGE_SHIFT) == offset; You'd probably have to iterate over the whole range (which might span multiple VMAs), but reading the discussion, I'm fine with dropping this patch for now. I think it's more important to document that thoroughly: what does it mean when we use GUEST_MEMFD_FLAG_SUPPORT_SHARED and then pass that fd in a memslot. Skimming over patch #15, I assume this is properly documented in there. -- Cheers, David / dhildenb