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[91.12.96.12]) by smtp.gmail.com with ESMTPSA id p5sm4479649wrd.25.2021.09.10.02.23.49 (version=TLS1_3 cipher=TLS_AES_128_GCM_SHA256 bits=128/128); Fri, 10 Sep 2021 02:23:49 -0700 (PDT) Subject: Re: [PATCH RFC 6/9] s390/pci_mmio: fully validate the VMA before calling follow_pte() To: Niklas Schnelle , linux-kernel@vger.kernel.org Cc: linux-s390@vger.kernel.org, kvm@vger.kernel.org, linux-mm@kvack.org References: <20210909145945.12192-1-david@redhat.com> <20210909145945.12192-7-david@redhat.com> <82d683ec361245e1879b3f14492cdd5c41957e52.camel@linux.ibm.com> From: David Hildenbrand Organization: Red Hat Message-ID: Date: Fri, 10 Sep 2021 11:23:48 +0200 User-Agent: Mozilla/5.0 (X11; Linux x86_64; rv:78.0) Gecko/20100101 Thunderbird/78.11.0 MIME-Version: 1.0 In-Reply-To: <82d683ec361245e1879b3f14492cdd5c41957e52.camel@linux.ibm.com> Content-Type: text/plain; charset=utf-8; format=flowed Content-Language: en-US Content-Transfer-Encoding: 7bit Precedence: bulk List-ID: X-Mailing-List: linux-s390@vger.kernel.org On 10.09.21 10:22, Niklas Schnelle wrote: > On Thu, 2021-09-09 at 16:59 +0200, David Hildenbrand wrote: >> We should not walk/touch page tables outside of VMA boundaries when >> holding only the mmap sem in read mode. Evil user space can modify the >> VMA layout just before this function runs and e.g., trigger races with >> page table removal code since commit dd2283f2605e ("mm: mmap: zap pages >> with read mmap_sem in munmap"). >> >> find_vma() does not check if the address is >= the VMA start address; >> use vma_lookup() instead. >> >> Fixes: dd2283f2605e ("mm: mmap: zap pages with read mmap_sem in munmap") >> Signed-off-by: David Hildenbrand >> --- >> arch/s390/pci/pci_mmio.c | 4 ++-- >> 1 file changed, 2 insertions(+), 2 deletions(-) >> >> diff --git a/arch/s390/pci/pci_mmio.c b/arch/s390/pci/pci_mmio.c >> index ae683aa623ac..c5b35ea129cf 100644 >> --- a/arch/s390/pci/pci_mmio.c >> +++ b/arch/s390/pci/pci_mmio.c >> @@ -159,7 +159,7 @@ SYSCALL_DEFINE3(s390_pci_mmio_write, unsigned long, mmio_addr, >> >> mmap_read_lock(current->mm); >> ret = -EINVAL; >> - vma = find_vma(current->mm, mmio_addr); >> + vma = vma_lookup(current->mm, mmio_addr); >> if (!vma) >> goto out_unlock_mmap; >> if (!(vma->vm_flags & (VM_IO | VM_PFNMAP))) >> @@ -298,7 +298,7 @@ SYSCALL_DEFINE3(s390_pci_mmio_read, unsigned long, mmio_addr, >> >> mmap_read_lock(current->mm); >> ret = -EINVAL; >> - vma = find_vma(current->mm, mmio_addr); >> + vma = vma_lookup(current->mm, mmio_addr); >> if (!vma) >> goto out_unlock_mmap; >> if (!(vma->vm_flags & (VM_IO | VM_PFNMAP))) > > Oh wow great find thanks! If I may say so these are not great function > names. Looking at the code vma_lookup() is inded find_vma() plus the > check that the looked up address is indeed inside the vma. > IIRC, vma_lookup() was introduced fairly recently. Before that, this additional check was open coded (and still are in some instances). It's confusing, I agree. > I think this is pretty independent of the rest of the patches, so do > you want me to apply this patch independently or do you want to wait > for the others? Sure, please go ahead and apply independently. It'd be great if you could give it a quick sanity test, although I don't expect surprises -- unfortunately, the environment I have easily at hand is not very well suited (#cpu, #mem, #disk ...) for anything that exceeds basic compile tests (and even cross-compiling is significantly faster ...). > > In any case: > > Reviewed-by: Niklas Schnelle > Thanks! -- Thanks, David / dhildenb