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Wed, 10 Jul 2024 14:14:06 -0700 (PDT) Received: from [10.35.209.243] ([208.115.86.71]) by smtp.gmail.com with ESMTPSA id d2e1a72fcca58-70b4397c02fsm4390228b3a.143.2024.07.10.14.14.04 (version=TLS1_3 cipher=TLS_AES_128_GCM_SHA256 bits=128/128); Wed, 10 Jul 2024 14:14:06 -0700 (PDT) Message-ID: Date: Wed, 10 Jul 2024 23:14:04 +0200 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 , Mike Rapoport Cc: seanjc@google.com, pbonzini@redhat.com, akpm@linux-foundation.org, dwmw@amazon.co.uk, 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, James Gowans References: <20240709132041.3625501-1-roypat@amazon.co.uk> <20240709132041.3625501-8-roypat@amazon.co.uk> <0dc45181-de7e-4d97-9178-573c6f683f55@redhat.com> <258b3b76-cf87-4dfc-bcfa-b2af94aba811@amazon.co.uk> From: David Hildenbrand Autocrypt: addr=david@redhat.com; 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charset=UTF-8; format=flowed Content-Transfer-Encoding: 7bit X-Rspamd-Server: rspam03 X-Rspam-User: X-Rspamd-Queue-Id: EEB0DA000A X-Stat-Signature: phjuretzxda9r7fbfd6nhqjyup348a8k X-HE-Tag: 1720646049-207320 X-HE-Meta: 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 SoQxrmtm HUmMEiN4opLneBLL8YJddQnHPUXhn968YeRxzsKwibXnpzEEdUyi6IqY7GjPMIfltzkyKtUxFe4bnqbjtsK/XdRaQWlGg6fxRfITAJaMRpePgDTdQrF2IZJHX0srA+XRIRkJmohIxSS7uI69+6qP9xfq7ZGTj4F3qjxjA9Xow88bCwQUqTbWUDWvNkSeSaTcNsDAb60P0+w1j2KYO4HBSNnUFs8zvSfQC4GpiiyJaXHjZ15s1EO/ebY8DCnb0wuB/ohs8JnlneKOEfxg+PSlEyCxC1Nici6oBuyVx8tWnJqIzdq2M+ggCuKqmH3TIqfX7x6nQ3S7KKYomyNWumDSKOlSl+kMESCmFJ5+L+sx51pyzNANKCeqsBZmkVmWA/J5Ga/gsJWd+3GBuafoAa2niAyQ5kYzlS/AnZxKp X-Bogosity: Ham, tests=bogofilter, spamicity=0.000000, version=1.2.4 Sender: owner-linux-mm@kvack.org Precedence: bulk X-Loop: owner-majordomo@kvack.org List-ID: List-Subscribe: List-Unsubscribe: On 10.07.24 11:50, Patrick Roy wrote: > > > On 7/10/24 08:32, Mike Rapoport wrote: >> CAUTION: This email originated from outside of the organization. Do not click links or open attachments unless you can confirm the sender and know the content is safe. >> >> >> >> On Tue, Jul 09, 2024 at 11:09:29PM +0200, David Hildenbrand wrote: >>> 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 >> >> I'm with David here. >> > > Right, that makes sense. My thinking here was that if memfd_secret and > potential mappings of guest_memfd have the same behavior wrt GUP, then > it makes sense to just have them rely on the same checks. But I guess I > didn't follow that thought to its logical conclusion of renaming the > "secretmem" checks into "inaccessible" checks and moving them out of > secretmem.h. > > Or do you mean to just leave secretmem untouched and add separate > "inaccessible" checks? But then we'd have two different ways of > disabling GUP for specific VMAs that both rely on checks in exactly the > same places :/ You can just replace the vma_is_secretmem in relevant places by checks if inaccessible address spaces. No need for the additional vma_is_secretmem check then. BUT, as raised in my other reply, I wonder if adding support for secretmem in KVM (I assume) would be simpler+cleaner. > >>> -- >>> Cheers, >>> >>> David / dhildenb >>> >> >> -- >> Sincerely yours, >> Mike. > -- Cheers, David / dhildenb