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Tue, 09 Jul 2024 14:09:35 -0700 (PDT) X-Google-Smtp-Source: AGHT+IFUIpwg0q5tX/615i6NZ/zZJubSifIfLGh41ui/wVdDDxeaKO6CBzN2Bumt/d0xd4q/gI7xDw== X-Received: by 2002:a05:6a20:a111:b0:1c0:e925:f3e1 with SMTP id adf61e73a8af0-1c2984c9de7mr4305537637.50.1720559374128; Tue, 09 Jul 2024 14:09:34 -0700 (PDT) Received: from [172.31.79.51] ([216.9.110.4]) by smtp.gmail.com with ESMTPSA id d2e1a72fcca58-70b438c70a4sm2290324b3a.83.2024.07.09.14.09.31 (version=TLS1_3 cipher=TLS_AES_128_GCM_SHA256 bits=128/128); Tue, 09 Jul 2024 14:09:33 -0700 (PDT) Message-ID: <0dc45181-de7e-4d97-9178-573c6f683f55@redhat.com> Date: Tue, 9 Jul 2024 23:09:29 +0200 Precedence: bulk X-Mailing-List: linux-kernel@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 User-Agent: Mozilla Thunderbird Subject: Re: [RFC PATCH 7/8] mm: secretmem: use AS_INACCESSIBLE to prohibit GUP To: Patrick Roy , seanjc@google.com, pbonzini@redhat.com, akpm@linux-foundation.org, dwmw@amazon.co.uk, rppt@kernel.org Cc: tglx@linutronix.de, mingo@redhat.com, bp@alien8.de, dave.hansen@linux.intel.com, x86@kernel.org, hpa@zytor.com, willy@infradead.org, graf@amazon.com, derekmn@amazon.com, kalyazin@amazon.com, kvm@vger.kernel.org, linux-kernel@vger.kernel.org, linux-mm@kvack.org, dmatlack@google.com, tabba@google.com, chao.p.peng@linux.intel.com, xmarcalx@amazon.co.uk References: <20240709132041.3625501-1-roypat@amazon.co.uk> <20240709132041.3625501-8-roypat@amazon.co.uk> 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 09.07.24 15:20, Patrick Roy wrote: > Inside of vma_is_secretmem and secretmem_mapping, instead of checking > whether a vm_area_struct/address_space has the secretmem ops structure > attached to it, check whether the address_space has the AS_INACCESSIBLE > bit set. Then set the AS_INACCESSIBLE flag for secretmem's > address_space. > > This means that get_user_pages and friends are disables for all > adress_spaces that set AS_INACCESIBLE. The AS_INACCESSIBLE flag was > introduced in commit c72ceafbd12c ("mm: Introduce AS_INACCESSIBLE for > encrypted/confidential memory") specifically for guest_memfd to indicate > that no reads and writes should ever be done to guest_memfd > address_spaces. Disallowing gup seems like a reasonable semantic > extension, and means that potential future mmaps of guest_memfd cannot > be GUP'd. > > Signed-off-by: Patrick Roy > --- > include/linux/secretmem.h | 13 +++++++++++-- > mm/secretmem.c | 6 +----- > 2 files changed, 12 insertions(+), 7 deletions(-) > > diff --git a/include/linux/secretmem.h b/include/linux/secretmem.h > index e918f96881f5..886c8f7eb63e 100644 > --- a/include/linux/secretmem.h > +++ b/include/linux/secretmem.h > @@ -8,10 +8,19 @@ extern const struct address_space_operations secretmem_aops; > > static inline bool secretmem_mapping(struct address_space *mapping) > { > - return mapping->a_ops == &secretmem_aops; > + return mapping->flags & AS_INACCESSIBLE; > +} > + > +static inline bool vma_is_secretmem(struct vm_area_struct *vma) > +{ > + struct file *file = vma->vm_file; > + > + if (!file) > + return false; > + > + return secretmem_mapping(file->f_inode->i_mapping); > } That sounds wrong. You should leave *secretmem alone and instead have something like inaccessible_mapping that is used where appropriate. vma_is_secretmem() should not suddenly succeed on something that is not mm/secretmem.c -- Cheers, David / dhildenb