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[79.242.52.210]) by smtp.gmail.com with ESMTPSA id 5b1f17b1804b1-4282bb97fbasm245003675e9.41.2024.08.06.07.08.26 (version=TLS1_3 cipher=TLS_AES_128_GCM_SHA256 bits=128/128); Tue, 06 Aug 2024 07:08:26 -0700 (PDT) Message-ID: Date: Tue, 6 Aug 2024 16:08:25 +0200 MIME-Version: 1.0 User-Agent: Mozilla Thunderbird Subject: Re: [PATCH RFC 3/4] mm: guest_memfd: Add option to remove guest private memory from direct map To: Elliot Berman , Andrew Morton , Paolo Bonzini , Sean Christopherson , Fuad Tabba , Patrick Roy , qperret@google.com, Ackerley Tng Cc: linux-coco@lists.linux.dev, linux-arm-msm@vger.kernel.org, linux-kernel@vger.kernel.org, linux-mm@kvack.org, kvm@vger.kernel.org References: <20240805-guest-memfd-lib-v1-0-e5a29a4ff5d7@quicinc.com> <20240805-guest-memfd-lib-v1-3-e5a29a4ff5d7@quicinc.com> From: David Hildenbrand Autocrypt: addr=david@redhat.com; keydata= xsFNBFXLn5EBEAC+zYvAFJxCBY9Tr1xZgcESmxVNI/0ffzE/ZQOiHJl6mGkmA1R7/uUpiCjJ dBrn+lhhOYjjNefFQou6478faXE6o2AhmebqT4KiQoUQFV4R7y1KMEKoSyy8hQaK1umALTdL QZLQMzNE74ap+GDK0wnacPQFpcG1AE9RMq3aeErY5tujekBS32jfC/7AnH7I0v1v1TbbK3Gp XNeiN4QroO+5qaSr0ID2sz5jtBLRb15RMre27E1ImpaIv2Jw8NJgW0k/D1RyKCwaTsgRdwuK Kx/Y91XuSBdz0uOyU/S8kM1+ag0wvsGlpBVxRR/xw/E8M7TEwuCZQArqqTCmkG6HGcXFT0V9 PXFNNgV5jXMQRwU0O/ztJIQqsE5LsUomE//bLwzj9IVsaQpKDqW6TAPjcdBDPLHvriq7kGjt WhVhdl0qEYB8lkBEU7V2Yb+SYhmhpDrti9Fq1EsmhiHSkxJcGREoMK/63r9WLZYI3+4W2rAc UucZa4OT27U5ZISjNg3Ev0rxU5UH2/pT4wJCfxwocmqaRr6UYmrtZmND89X0KigoFD/XSeVv jwBRNjPAubK9/k5NoRrYqztM9W6sJqrH8+UWZ1Idd/DdmogJh0gNC0+N42Za9yBRURfIdKSb B3JfpUqcWwE7vUaYrHG1nw54pLUoPG6sAA7Mehl3nd4pZUALHwARAQABzSREYXZpZCBIaWxk ZW5icmFuZCA8ZGF2aWRAcmVkaGF0LmNvbT7CwZgEEwEIAEICGwMGCwkIBwMCBhUIAgkKCwQW AgMBAh4BAheAAhkBFiEEG9nKrXNcTDpGDfzKTd4Q9wD/g1oFAl8Ox4kFCRKpKXgACgkQTd4Q 9wD/g1oHcA//a6Tj7SBNjFNM1iNhWUo1lxAja0lpSodSnB2g4FCZ4R61SBR4l/psBL73xktp rDHrx4aSpwkRP6Epu6mLvhlfjmkRG4OynJ5HG1gfv7RJJfnUdUM1z5kdS8JBrOhMJS2c/gPf wv1TGRq2XdMPnfY2o0CxRqpcLkx4vBODvJGl2mQyJF/gPepdDfcT8/PY9BJ7FL6Hrq1gnAo4 3Iv9qV0JiT2wmZciNyYQhmA1V6dyTRiQ4YAc31zOo2IM+xisPzeSHgw3ONY/XhYvfZ9r7W1l pNQdc2G+o4Di9NPFHQQhDw3YTRR1opJaTlRDzxYxzU6ZnUUBghxt9cwUWTpfCktkMZiPSDGd KgQBjnweV2jw9UOTxjb4LXqDjmSNkjDdQUOU69jGMUXgihvo4zhYcMX8F5gWdRtMR7DzW/YE BgVcyxNkMIXoY1aYj6npHYiNQesQlqjU6azjbH70/SXKM5tNRplgW8TNprMDuntdvV9wNkFs 9TyM02V5aWxFfI42+aivc4KEw69SE9KXwC7FSf5wXzuTot97N9Phj/Z3+jx443jo2NR34XgF 89cct7wJMjOF7bBefo0fPPZQuIma0Zym71cP61OP/i11ahNye6HGKfxGCOcs5wW9kRQEk8P9 M/k2wt3mt/fCQnuP/mWutNPt95w9wSsUyATLmtNrwccz63XOwU0EVcufkQEQAOfX3n0g0fZz Bgm/S2zF/kxQKCEKP8ID+Vz8sy2GpDvveBq4H2Y34XWsT1zLJdvqPI4af4ZSMxuerWjXbVWb T6d4odQIG0fKx4F8NccDqbgHeZRNajXeeJ3R7gAzvWvQNLz4piHrO/B4tf8svmRBL0ZB5P5A 2uhdwLU3NZuK22zpNn4is87BPWF8HhY0L5fafgDMOqnf4guJVJPYNPhUFzXUbPqOKOkL8ojk CXxkOFHAbjstSK5Ca3fKquY3rdX3DNo+EL7FvAiw1mUtS+5GeYE+RMnDCsVFm/C7kY8c2d0G NWkB9pJM5+mnIoFNxy7YBcldYATVeOHoY4LyaUWNnAvFYWp08dHWfZo9WCiJMuTfgtH9tc75 7QanMVdPt6fDK8UUXIBLQ2TWr/sQKE9xtFuEmoQGlE1l6bGaDnnMLcYu+Asp3kDT0w4zYGsx 5r6XQVRH4+5N6eHZiaeYtFOujp5n+pjBaQK7wUUjDilPQ5QMzIuCL4YjVoylWiBNknvQWBXS lQCWmavOT9sttGQXdPCC5ynI+1ymZC1ORZKANLnRAb0NH/UCzcsstw2TAkFnMEbo9Zu9w7Kv AxBQXWeXhJI9XQssfrf4Gusdqx8nPEpfOqCtbbwJMATbHyqLt7/oz/5deGuwxgb65pWIzufa N7eop7uh+6bezi+rugUI+w6DABEBAAHCwXwEGAEIACYCGwwWIQQb2cqtc1xMOkYN/MpN3hD3 AP+DWgUCXw7HsgUJEqkpoQAKCRBN3hD3AP+DWrrpD/4qS3dyVRxDcDHIlmguXjC1Q5tZTwNB boaBTPHSy/Nksu0eY7x6HfQJ3xajVH32Ms6t1trDQmPx2iP5+7iDsb7OKAb5eOS8h+BEBDeq 3ecsQDv0fFJOA9ag5O3LLNk+3x3q7e0uo06XMaY7UHS341ozXUUI7wC7iKfoUTv03iO9El5f XpNMx/YrIMduZ2+nd9Di7o5+KIwlb2mAB9sTNHdMrXesX8eBL6T9b+MZJk+mZuPxKNVfEQMQ a5SxUEADIPQTPNvBewdeI80yeOCrN+Zzwy/Mrx9EPeu59Y5vSJOx/z6OUImD/GhX7Xvkt3kq Er5KTrJz3++B6SH9pum9PuoE/k+nntJkNMmQpR4MCBaV/J9gIOPGodDKnjdng+mXliF3Ptu6 3oxc2RCyGzTlxyMwuc2U5Q7KtUNTdDe8T0uE+9b8BLMVQDDfJjqY0VVqSUwImzTDLX9S4g/8 kC4HRcclk8hpyhY2jKGluZO0awwTIMgVEzmTyBphDg/Gx7dZU1Xf8HFuE+UZ5UDHDTnwgv7E th6RC9+WrhDNspZ9fJjKWRbveQgUFCpe1sa77LAw+XFrKmBHXp9ZVIe90RMe2tRL06BGiRZr jPrnvUsUUsjRoRNJjKKA/REq+sAnhkNPPZ/NNMjaZ5b8Tovi8C0tmxiCHaQYqj7G2rgnT0kt WNyWQQ== Organization: Red Hat In-Reply-To: <20240805-guest-memfd-lib-v1-3-e5a29a4ff5d7@quicinc.com> X-Mimecast-Spam-Score: 0 X-Mimecast-Originator: redhat.com Content-Language: en-US Content-Type: text/plain; charset=UTF-8; format=flowed Content-Transfer-Encoding: 7bit X-Stat-Signature: 8xhzkurk5q1eepwzx7njgi8m9sfqw8pu X-Rspamd-Queue-Id: 45A4D14001A X-Rspam-User: X-Rspamd-Server: rspam08 X-HE-Tag: 1722953311-734441 X-HE-Meta: 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 AvI7wO8S 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 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 05.08.24 20:34, Elliot Berman wrote: > This patch was reworked from Patrick's patch: > https://lore.kernel.org/all/20240709132041.3625501-6-roypat@amazon.co.uk/ > > While guest_memfd is not available to be mapped by userspace, it is > still accessible through the kernel's direct map. This means that in > scenarios where guest-private memory is not hardware protected, it can > be speculatively read and its contents potentially leaked through > hardware side-channels. Removing guest-private memory from the direct > map, thus mitigates a large class of speculative execution issues > [1, Table 1]. I think you have to point out here that the speculative execution issues are primarily only an issue when guest_memfd private memory is used without TDX and friends where the memory would be encrypted either way. Or am I wrong? > > Direct map removal do not reuse the `.prepare` machinery, since > `prepare` can be called multiple time, and it is the responsibility of > the preparation routine to not "prepare" the same folio twice [2]. Thus, > instead explicitly check if `filemap_grab_folio` allocated a new folio, > and remove the returned folio from the direct map only if this was the > case. > > The patch uses release_folio instead of free_folio to reinsert pages > back into the direct map as by the time free_folio is called, > folio->mapping can already be NULL. This means that a call to > folio_inode inside free_folio might deference a NULL pointer, leaving no > way to access the inode which stores the flags that allow determining > whether the page was removed from the direct map in the first place. > > [1]: https://download.vusec.net/papers/quarantine_raid23.pdf > > Cc: Patrick Roy > Signed-off-by: Elliot Berman > --- > include/linux/guest_memfd.h | 8 ++++++ > mm/guest_memfd.c | 65 ++++++++++++++++++++++++++++++++++++++++++++- > 2 files changed, 72 insertions(+), 1 deletion(-) > > diff --git a/include/linux/guest_memfd.h b/include/linux/guest_memfd.h > index be56d9d53067..f9e4a27aed67 100644 > --- a/include/linux/guest_memfd.h > +++ b/include/linux/guest_memfd.h > @@ -25,6 +25,14 @@ struct guest_memfd_operations { > int (*release)(struct inode *inode); > }; > > +/** > + * @GUEST_MEMFD_FLAG_NO_DIRECT_MAP: When making folios inaccessible by host, also > + * remove them from the kernel's direct map. > + */ Should we start introducing the concept of private and shared first, such that we can then say that this only applies to private memory? > +enum { > + GUEST_MEMFD_FLAG_NO_DIRECT_MAP = BIT(0), > +}; > + > /** > * @GUEST_MEMFD_GRAB_UPTODATE: Ensure pages are zeroed/up to date. > * If trusted hyp will do it, can ommit this flag > diff --git a/mm/guest_memfd.c b/mm/guest_memfd.c > index 580138b0f9d4..e9d8cab72b28 100644 > --- a/mm/guest_memfd.c > +++ b/mm/guest_memfd.c > @@ -7,9 +7,55 @@ > #include > #include > #include > +#include > + > +static inline int guest_memfd_folio_private(struct folio *folio) > +{ > + unsigned long nr_pages = folio_nr_pages(folio); guest_memfd only supports small folios, this can be simplified. > + unsigned long i; > + int r; > + > + for (i = 0; i < nr_pages; i++) { > + struct page *page = folio_page(folio, i); > + > + r = set_direct_map_invalid_noflush(page); > + if (r < 0) > + goto out_remap; > + } > + > + folio_set_private(folio); > + return 0; > +out_remap: > + for (; i > 0; i--) { > + struct page *page = folio_page(folio, i - 1); > + > + BUG_ON(set_direct_map_default_noflush(page)); > + } > + return r; > +} > + > +static inline void guest_memfd_folio_clear_private(struct folio *folio) Set set/clear private semantics in this context are a bit confusing. I assume you mean "make inaccessible" "make accessible" and using the PG_private flag is just an implementation detail. > +{ > + unsigned long start = (unsigned long)folio_address(folio); > + unsigned long nr = folio_nr_pages(folio); > + unsigned long i; > + > + if (!folio_test_private(folio)) > + return; > + > + for (i = 0; i < nr; i++) { > + struct page *page = folio_page(folio, i); > + > + BUG_ON(set_direct_map_default_noflush(page)); > + } > + flush_tlb_kernel_range(start, start + folio_size(folio)); > + > + folio_clear_private(folio); > +} > > struct folio *guest_memfd_grab_folio(struct file *file, pgoff_t index, u32 flags) > { > + unsigned long gmem_flags = (unsigned long)file->private_data; > struct inode *inode = file_inode(file); > struct guest_memfd_operations *ops = inode->i_private; > struct folio *folio; > @@ -43,6 +89,12 @@ struct folio *guest_memfd_grab_folio(struct file *file, pgoff_t index, u32 flags > goto out_err; > } > > + if (gmem_flags & GUEST_MEMFD_FLAG_NO_DIRECT_MAP) { > + r = guest_memfd_folio_private(folio); > + if (r) > + goto out_err; > + } > + > /* > * Ignore accessed, referenced, and dirty flags. The memory is > * unevictable and there is no storage to write back to. > @@ -213,14 +265,25 @@ static bool gmem_release_folio(struct folio *folio, gfp_t gfp) > if (ops->invalidate_end) > ops->invalidate_end(inode, offset, nr); > > + guest_memfd_folio_clear_private(folio); > + > return true; > } > > +static void gmem_invalidate_folio(struct folio *folio, size_t offset, size_t len) > +{ > + /* not yet supported */ > + BUG_ON(offset || len != folio_size(folio)); > + > + BUG_ON(!gmem_release_folio(folio, 0)); In general, no BUG_ON please. WARN_ON_ONCE() is sufficient. > +} > + > static const struct address_space_operations gmem_aops = { > .dirty_folio = noop_dirty_folio, > .migrate_folio = gmem_migrate_folio, > .error_remove_folio = gmem_error_folio, > .release_folio = gmem_release_folio, > + .invalidate_folio = gmem_invalidate_folio, > }; > > static inline bool guest_memfd_check_ops(const struct guest_memfd_operations *ops) > @@ -241,7 +304,7 @@ struct file *guest_memfd_alloc(const char *name, > if (!guest_memfd_check_ops(ops)) > return ERR_PTR(-EINVAL); > > - if (flags) > + if (flags & ~GUEST_MEMFD_FLAG_NO_DIRECT_MAP) > return ERR_PTR(-EINVAL); > > /* > -- Cheers, David / dhildenb