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[91.12.103.110]) by smtp.gmail.com with ESMTPSA id f16sm2169829wrr.53.2021.10.08.03.46.17 (version=TLS1_3 cipher=TLS_AES_128_GCM_SHA256 bits=128/128); Fri, 08 Oct 2021 03:46:17 -0700 (PDT) Subject: Re: [PATCH] mm: Fix NULL page->mapping dereference in page_is_secretmem() To: Sean Christopherson , Andrew Morton Cc: linux-kernel@vger.kernel.org, Mike Rapoport , linux-mm@kvack.org, "Darrick J . Wong" , Stephen References: <20211007231502.3552715-1-seanjc@google.com> From: David Hildenbrand Organization: Red Hat Message-ID: <97f7ae02-3124-8de5-f614-a2f7891645a5@redhat.com> Date: Fri, 8 Oct 2021 12:46:17 +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: <20211007231502.3552715-1-seanjc@google.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-kernel@vger.kernel.org On 08.10.21 01:15, Sean Christopherson wrote: > Check for a NULL page->mapping before dereferencing the mapping in > page_is_secretmem(), as the page's mapping can be nullified while gup() > is running, e.g. by reclaim or truncation. > > BUG: kernel NULL pointer dereference, address: 0000000000000068 > #PF: supervisor read access in kernel mode > #PF: error_code(0x0000) - not-present page > PGD 0 P4D 0 > Oops: 0000 [#1] PREEMPT SMP NOPTI > CPU: 6 PID: 4173897 Comm: CPU 3/KVM Tainted: G W > RIP: 0010:internal_get_user_pages_fast+0x621/0x9d0 > Code: <48> 81 7a 68 80 08 04 bc 0f 85 21 ff ff 8 89 c7 be > RSP: 0018:ffffaa90087679b0 EFLAGS: 00010046 > RAX: ffffe3f37905b900 RBX: 00007f2dd561e000 RCX: ffffe3f37905b934 > RDX: 0000000000000000 RSI: 0000000000000000 RDI: ffffe3f37905b900 > ... > CR2: 0000000000000068 CR3: 00000004c5898003 CR4: 00000000001726e0 > Call Trace: > get_user_pages_fast_only+0x13/0x20 > hva_to_pfn+0xa9/0x3e0 > try_async_pf+0xa1/0x270 > direct_page_fault+0x113/0xad0 > kvm_mmu_page_fault+0x69/0x680 > vmx_handle_exit+0xe1/0x5d0 > kvm_arch_vcpu_ioctl_run+0xd81/0x1c70 > kvm_vcpu_ioctl+0x267/0x670 > __x64_sys_ioctl+0x83/0xa0 > do_syscall_64+0x56/0x80 > entry_SYSCALL_64_after_hwframe+0x44/0xae > > Cc: Mike Rapoport > Cc: linux-mm@kvack.org > Reported-by: Darrick J. Wong > Reported-by: Stephen > Tested-by: Darrick J. Wong > Signed-off-by: Sean Christopherson > --- > include/linux/secretmem.h | 2 +- > 1 file changed, 1 insertion(+), 1 deletion(-) > > diff --git a/include/linux/secretmem.h b/include/linux/secretmem.h > index 21c3771e6a56..988528b5da43 100644 > --- a/include/linux/secretmem.h > +++ b/include/linux/secretmem.h > @@ -23,7 +23,7 @@ static inline bool page_is_secretmem(struct page *page) > mapping = (struct address_space *) > ((unsigned long)page->mapping & ~PAGE_MAPPING_FLAGS); > > - if (mapping != page->mapping) > + if (!mapping || mapping != page->mapping) > return false; > > return mapping->a_ops == &secretmem_aops; > I assume we want to add Fixes: 1507f51255c9 ("mm: introduce memfd_secret system call to create "secret" memory areas") Cc: # v5.14 Reviewed-by: David Hildenbrand -- Thanks, David / dhildenb