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[2003:d8:2f30:ec00:8f7e:58a4:ebf0:6a36]) by smtp.gmail.com with ESMTPSA id ffacd0b85a97d-3a4eace22c6sm1681272f8f.81.2025.05.28.08.02.16 (version=TLS1_3 cipher=TLS_AES_128_GCM_SHA256 bits=128/128); Wed, 28 May 2025 08:02:16 -0700 (PDT) Message-ID: <5b9f5952-9979-426f-857a-dffa9b7963af@redhat.com> Date: Wed, 28 May 2025 17:02:15 +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> 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: qlN0GvxDlZdKnWFcFXTqs48-W7DIEg0zjEJPWs_9nZQ_1748444538 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: rspam03 X-Rspamd-Queue-Id: 920A1100002 X-Stat-Signature: n7ahod8fj7ntnrr8dm1nu5oqfjmd3bx4 X-Rspam-User: X-HE-Tag: 1748444541-559839 X-HE-Meta: U2FsdGVkX1+zjbxLh33B6WJvt0M4ur4BGMmYXO5lNeQ5ksekAsxNce8/U5bdbxi59GVVlA0d2QRH8fmmGsHeGPSAx2jr7PO8q5qJNrStTzq5GCs3o1hhNrsjYEBjlTZ9vIVQMjtgNhFyro8JjdKXGHO9Oe8doHsgT+q8jNxojEi0OACidiHeTRiv1fgEq+zBfnOSv7wLe59iCsdATSx0wjD9Kv4QKk7M9tY3gF0JhrKYfBwc9neseYt473yOMJhjOe9BQ/nJxdEvSmqZlrL+Y5nC+kgPXAa12voHbvd0gVuurh6T9+w1ilT8sHXHCdRodwIP2iyRhfY/189g+UdCkT7DQbqlQKdUCTsbXUo848K2vaRw8BM9TKA4eywejImhcC499tx5+1llTBmw6W3pXe15WfUuKWlIyG/SHf2ToIKym5vbwpOyVvOwBIlq/subXsGIlIJ8bAtsvFCuULEu6ATgH6zKrA/WrSZJgCavnQW+BOFR4OD54ncetkmAEr0E+GkxRVX+yMNA++3RNAiLKPgC9TdpWuzmnqqWkFev23BzZly9Vmk3eOtZiRfqX0QszCoAgU/zQW8JqVV3qccY/bTy+tAbbblfwZQzCGtLj52Bd6FeHkVTy6N3KSKbiqEwI73bmfQqNl3+adfW0PrDdiM1f882qgx6gIJGEcJAT1jdj/b0EYmx7EAwiVTFqxvwr7VA355wB/UPEfJBIcnMR7MPpxLq0oC3AuSMRyqarSU6mKQh4AOMAtwC7GbOfwL76eb6iShOeB0tElc3tg+nVzV+LmFtcpaL20WOiK4uuJT4SZgqn4vCY7x3TTNR93/pXiXYV83BMgNhaKkscYdBJ62qny5Y0R3ktHyAAf20TmQe6CbtM24NPD+J/NtZ22Ec/noJULrz8AYuCqM5kZAEA9jkPA5X+5LvEr6T31+2DTJqxE0LzQo4W9pCH7ZX6+I0nQ937lRG2LrP8Fm7WRh wkUlsCtb VnnLxYOr4vnznodnQvQUgyV1KT2yWs0a8W/64/Tr62AXzUnARuom0adU2My2WcqzF970sl5jX5FgPOyE/1D/VDeJJZKFlyT66l9F6R80/sM99q0czPiTcu97THHW22qQAAQpQ 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 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. > > 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? Confusing. > > Sligtly off-topic: it's also a bit confusing to me on whether the driver > should set VM_IO for VM_MIXEDMAP. I think it should because VM_IO says: Depends on the driver. Some VM_MIXEDMAP users only map ordinary kernel allocations, where VM_IO is not required. For these drivers, I really don't know. -- Cheers, David / dhildenb