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[2003:d8:2f30:ec00:8f7e:58a4:ebf0:6a36]) by smtp.gmail.com with ESMTPSA id ffacd0b85a97d-3a4eac8add9sm1822265f8f.54.2025.05.28.08.29.30 (version=TLS1_3 cipher=TLS_AES_128_GCM_SHA256 bits=128/128); Wed, 28 May 2025 08:29:30 -0700 (PDT) Message-ID: Date: Wed, 28 May 2025 17:29:29 +0200 MIME-Version: 1.0 User-Agent: Mozilla Thunderbird Subject: Re: [PATCH] mm: fix COW mapping handing in generic_access_phys To: Peter Xu Cc: Jinjiang Tu , akpm@linux-foundation.org, lorenzo.stoakes@oracle.com, Liam.Howlett@oracle.com, vbabka@suse.cz, rppt@kernel.org, surenb@google.com, mhocko@suse.com, linux-mm@kvack.org, wangkefeng.wang@huawei.com References: <20250528015617.302681-1-tujinjiang@huawei.com> <0d4f0180-52e6-47c9-b141-54e7e7c86880@redhat.com> <5b9f5952-9979-426f-857a-dffa9b7963af@redhat.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: X-Mimecast-Spam-Score: 0 X-Mimecast-MFC-PROC-ID: 3TUj_lQsqQJVzQundVMpmnNvOJHWqlk7fJf60Slbzgo_1748446172 X-Mimecast-Originator: redhat.com Content-Language: en-US Content-Type: text/plain; charset=UTF-8; format=flowed Content-Transfer-Encoding: 7bit X-Rspamd-Server: rspam06 X-Rspamd-Queue-Id: 083DFC0014 X-Stat-Signature: z6zfstz9nziuf65t6m3673d58e4dbsop X-Rspam-User: X-HE-Tag: 1748446174-379834 X-HE-Meta: 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 27G5O+qP 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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 28.05.25 17:25, Peter Xu wrote: > On Wed, May 28, 2025 at 05:02:15PM +0200, David Hildenbrand wrote: >> On 28.05.25 16:54, Peter Xu wrote: >>> [Add Jason] >>> >>> On Wed, May 28, 2025 at 11:59:56AM +0200, David Hildenbrand wrote: >>>> On 28.05.25 10:59, David Hildenbrand wrote: >>>>> On 28.05.25 03:56, Jinjiang Tu wrote: >>>>>> Syzkaller reports a below BUG: >>>>>> ioremap on RAM at 0x0000000022727000 - 0x0000000022727fff >>>>>> WARNING: CPU: 3 PID: 3609 at arch/x86/mm/ioremap.c:216 __ioremap_caller+0x644/0x7f0 arch/x86/mm/ioremap.c:216 >>>>>> Modules linked in: >>>>>> CPU: 3 PID: 3609 Comm: syz.2.577 Not tainted 6.6.0+ #63 >>>>>> Hardware name: QEMU Standard PC (i440FX + PIIX, 1996), BIOS rel-1.14.0-0-g155821a1990b-prebuilt.qemu.org 04/01/2014 >>>>>> RIP: 0010:__ioremap_caller+0x644/0x7f0 arch/x86/mm/ioremap.c:216 >>>>>> Call Trace: >>>>>> >>>>>> generic_access_phys+0x241/0x480 mm/memory.c:6458 >>>>>> __access_remote_vm+0x6af/0x970 mm/memory.c:6535 >>>>>> access_process_vm+0x53/0x80 mm/memory.c:6600 >>>>>> get_cmdline+0x192/0x380 mm/util.c:1041 >>>>>> audit_log_proctitle kernel/auditsc.c:1620 [inline] >>>>>> audit_log_exit+0x1424/0x18c0 kernel/auditsc.c:1811 >>>>>> __audit_syscall_exit+0x252/0x2f0 kernel/auditsc.c:2079 >>>>>> audit_syscall_exit include/linux/audit.h:356 [inline] >>>>>> syscall_exit_work+0x10f/0x130 kernel/entry/common.c:166 >>>>>> __syscall_exit_to_user_mode_work kernel/entry/common.c:205 [inline] >>>>>> syscall_exit_to_user_mode+0x10/0x1e0 kernel/entry/common.c:218 >>>>>> do_syscall_64+0x66/0x110 arch/x86/entry/common.c:87 >>>>>> entry_SYSCALL_64_after_hwframe+0x78/0xe2 >>>>>> >>>>>> The /dev/mem is mapped with COW mapping, and mremap at the mm->args_start. >>>>>> The special pfn mapping is replaced by anon folios due to COW. >>>>>> generic_access_phys() is supposed to handle iomem, instead of RAM pfn, >>>>>> thus trigger a WARN_ON. >>>>>> >>>>>> Similar to commit 04c35ab3bdae ("x86/mm/pat: fix VM_PAT handling in >>>>>> COW mappings"). check if the pte is special to reject Cowed anon folios. >>>>>> >>>>>> Signed-off-by: Jinjiang Tu >>>>>> --- >>>>>> mm/memory.c | 7 +++++++ >>>>>> 1 file changed, 7 insertions(+) >>>>>> >>>>>> diff --git a/mm/memory.c b/mm/memory.c >>>>>> index 49199410805c..e1dac84536ee 100644 >>>>>> --- a/mm/memory.c >>>>>> +++ b/mm/memory.c >>>>>> @@ -6840,6 +6840,13 @@ int generic_access_phys(struct vm_area_struct *vma, unsigned long addr, >>>>>> retry: >>>>>> if (follow_pfnmap_start(&args)) >>>>>> return -EINVAL; >>>>>> + >>>>>> + /* Never return PFNs of anon folios in COW mappings. */ >>>>>> + if (!args.special) { >>>>>> + follow_pfnmap_end(&args); >>>>>> + return -EINVAL; >>>>>> + } >>>>>> + >>>>>> prot = args.pgprot; >>>>>> phys_addr = (resource_size_t)args.pfn << PAGE_SHIFT; >>>>>> writable = args.writable; >>>>> >>>>> I assume we trigger this through vma->vm_ops->access, when the vm_ops have generic_access_phys set. >>>>> >>>>> I still dislike exposing the "special" bit here, as it is absolutely not what we should care about in the caller. >>>>> >>>>> In case our arch does not support pte_special, you fix will not catch that case ... >>>>> >>>>> The following might be better: >>>>> >>>>> diff --git a/mm/memory.c b/mm/memory.c >>>>> index 37d8738f5e12e..810adb8d1a53b 100644 >>>>> --- a/mm/memory.c >>>>> +++ b/mm/memory.c >>>>> @@ -6681,6 +6681,14 @@ int generic_access_phys(struct vm_area_struct *vma, unsigned long addr, >>>>> prot = args.pgprot; >>>>> phys_addr = (resource_size_t)args.pfn << PAGE_SHIFT; >>>>> writable = args.writable; >>>>> + >>>>> + /* Refuse (refcounted) anonymous pages in CoW mappings. */ >>>>> + if (is_cow_mapping(vma->vm_flags) && >>>>> + vm_normal_page(vma, addr, ptep_get(args.ptep))) { >>>>> + follow_pfnmap_end(&args); >>>>> + return -EINVAL; >>>>> + } >>>>> + >>>> >>>> Thinking again, we might have a PMD/PUD mapping, so maybe >>>> follow_pfnmap_start() should really just refuse any refcounted pages. > > [1] > >>> >>> We may want to be careful on this. >>> >>> I feel like we can still potentially break drivers that >>> follow_pfnmap_start() used to work on debateable things like RAM page >>> injections, unless breaking them is the intention. >> >> Yes, that all needs a cleanup likely; it's all very confusing and >> inconsistent. >> >>> >>> OTOH, I also see at least two in-tree drivers set VM_IO|VM_MIXEDMAP: >>> >>> *** drivers/gpu/drm/gma500/fbdev.c: >>> psb_fbdev_fb_mmap[110] vm_flags_set(vma, VM_IO | VM_MIXEDMAP | VM_DONTEXPAND | VM_DONTDUMP); >>> >>> *** drivers/gpu/drm/omapdrm/omap_gem.c: >>> omap_gem_object_mmap[538] vm_flags_set(vma, VM_DONTEXPAND | VM_DONTDUMP | VM_IO | VM_MIXEDMAP); >>> >>> AFAIU, these MIXEDMAP users will still rely on follow_pfnmap_start() to >>> work on e.g. RAM pages, because GUP will simply fail them.. >> >> Right. >> >> VM_IO essentially tells us "don't touch this memory, it might have side >> effects", such as MMIO, that's why GUP outright refuses VM_IO VMAs. >> >> I am not sure why generic_access_phys() should be allowed to ... touch that >> memory instead? > > I'm looking at: > > commit 28b2ee20c7cba812b6f2ccf6d722cf86d00a84dc > Author: Rik van Riel > Date: Wed Jul 23 21:27:05 2008 -0700 > > access_process_vm device memory infrastructure > > VM_IO is also intentionally mentioned in the doc too: > > Documentation/filesystems/locking.rst > > ->access() is called when get_user_pages() fails in > access_process_vm(), typically used to debug a process through > /proc/pid/mem or ptrace. This function is needed only for > VM_IO | VM_PFNMAP VMAs. > > So it definitely looks like intentional, though I know nothing about PPC > Cell SPUs.. VM_IO | VM_PFNMAP, I can understand that. It's weird combined with weird. But the use case for "VM_IO | VM_MIXEDMAP" ? To be precise, I am questioning if follow_pfnmap_start() should only work on ... PFNMAPs ? :) -- Cheers, David / dhildenb