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[2003:d8:2f0a:2e00:89cb:c7f0:82f2:e43c]) by smtp.gmail.com with ESMTPSA id 5b1f17b1804b1-454d50fb874sm98500685e9.28.2025.07.11.14.34.34 (version=TLS1_3 cipher=TLS_AES_128_GCM_SHA256 bits=128/128); Fri, 11 Jul 2025 14:34:35 -0700 (PDT) Message-ID: Date: Fri, 11 Jul 2025 23:34:34 +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: [PATCH 1/1] uprobes: relax valid_vma check for VM_MAYSHARE To: Matt Gilbride , Peter Zijlstra , Ingo Molnar , Arnaldo Carvalho de Melo , Mark Rutland , Alexander Shishkin , Jiri Olsa , Namhyung Kim Cc: linux-perf-users@vger.kernel.org, linux-kernel@vger.kernel.org, Andrii Nakryiko References: <20250711200705.1545447-1-mattgilbride@google.com> From: David Hildenbrand Content-Language: en-US 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: <20250711200705.1545447-1-mattgilbride@google.com> Content-Type: text/plain; charset=UTF-8; format=flowed Content-Transfer-Encoding: 7bit On 11.07.25 22:07, Matt Gilbride wrote: > `valid_vma` returns false when registering a uprobe if the provided VMA > is writable (`VM_WRITE`) or sharable (`VM_MAYSHARE`). This causes > `perf_event_open` [1] sys calls to fail silently. A successful return > code is delivered to the caller even though the uprobe wasn't actually > attached [2][3]. > > Remove the latter restriction (`VM_MAYSHARE`) from this check to allow > registering uprobes on code that has been "dual mapped" into a > process' memory space. This is helpful when instrumenting just-in-time > compiled code such as that of Android Runtime (ART) [4]. ART maps a > memfd twice, once as RW and once as RX, to uphold W^X for security > (defense in depth), and also to provide better performance (no need to > call `mprotect` before and after writing) [5]. > > uprobes already work for code that is ahead-of-time (AOT) compiled by > the Android Runtime (ART), as it resides in a static ELF file [6]. In > order to attach to just-in-time (JIT) compiled code, the Android OS itself > can coordinate with ART to isolate to-be-instrumented code in a separate > memfd, which will be left untouched for the duration of a uprobe being > attached. Thus, while the VMAs inside the memfd will *technically* have > the `VM_MAYSHARE` flag, the system will ensure that they will not be > written to again until after any uprobe as been detached. > > Link: https://man7.org/linux/man-pages/man2/perf_event_open.2.html [1] > Link: https://github.com/torvalds/linux/blob/088d13246a4672bc03aec664675138e3f5bff68c/kernel/events/uprobes.c#L1197-L1199 [2] > Link: https://github.com/torvalds/linux/blob/088d13246a4672bc03aec664675138e3f5bff68c/kernel/events/uprobes.c#L1256-L1268 [3] > Link: https://source.android.com/docs/core/runtime/jit-compiler [4] > Link: http://cs.android.com/android/platform/superproject/main/+/main:art/runtime/jit/jit_memory_region.cc;l=111-137?q=jit_memory_region.cc [5] > Link: https://source.android.com/docs/core/runtime#AOT_compilation [6] > Signed-off-by: Matt Gilbride > --- > We've created a working proof-of-concept in Android that demonstrates > what is described in the last paragraph of the commit message. Thus, we > introduce this patch to understand the reasoning behind the original > `VM_SHARED` (later converted to `VM_MAYSHARE`) restriction, and the risks > that may be associated with relaxing it. It's not clear to me why the > restriction is there, and we'd like to get feedback on why it is or is > not still relevant. > > kernel/events/uprobes.c | 2 +- > 1 file changed, 1 insertion(+), 1 deletion(-) > > diff --git a/kernel/events/uprobes.c b/kernel/events/uprobes.c > index a8caaea07ac37..1ecb3fdb853b9 100644 > --- a/kernel/events/uprobes.c > +++ b/kernel/events/uprobes.c > @@ -123,7 +123,7 @@ struct xol_area { > */ > static bool valid_vma(struct vm_area_struct *vma, bool is_register) > { > - vm_flags_t flags = VM_HUGETLB | VM_MAYEXEC | VM_MAYSHARE; > + vm_flags_t flags = VM_HUGETLB | VM_MAYEXEC; > > if (is_register) > flags |= VM_WRITE; It cannot possibly work, unless I am missing something important. You probably tested this against a kernel pre-6e3092d788be1de0aac56b81fc17551c76645cdf. Before that rework, you would be inserting anonymous pages in shared mappings, which is pretty much broken. If you want a double RX mapping where you can have anon pages in it, create that one as MAP_PRIVATE. -- Cheers, David / dhildenb