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[2003:cb:c720:ed00:a9b3:5954:823e:3427]) by smtp.gmail.com with ESMTPSA id ffacd0b85a97d-3912c103f41sm18750782f8f.85.2025.03.11.13.02.49 (version=TLS1_3 cipher=TLS_AES_128_GCM_SHA256 bits=128/128); Tue, 11 Mar 2025 13:02:50 -0700 (PDT) Message-ID: <03a7797a-75a0-4b45-b5b0-bf8bfb7f0955@redhat.com> Date: Tue, 11 Mar 2025 21:02:49 +0100 MIME-Version: 1.0 User-Agent: Mozilla Thunderbird Subject: Re: [PATCH -next v1 3/3] kernel/events/uprobes: uprobe_write_opcode() rewrite To: Oleg Nesterov Cc: linux-kernel@vger.kernel.org, linux-mm@kvack.org, linux-arm-kernel@lists.infradead.org, linux-trace-kernel@vger.kernel.org, linux-perf-users@vger.kernel.org, Andrew Morton , Matthew Wilcox , Russell King , Masami Hiramatsu , Peter Zijlstra , Ingo Molnar , Arnaldo Carvalho de Melo , Namhyung Kim , Mark Rutland , Alexander Shishkin , Jiri Olsa , Ian Rogers , Adrian Hunter , "Liang, Kan" , Tong Tiangen References: <20250304154846.1937958-1-david@redhat.com> <20250304154846.1937958-4-david@redhat.com> <20250310170320.GC26382@redhat.com> <79ec5aa9-1937-436e-8cf4-436746142f7b@redhat.com> <20250311123241.GB3493@redhat.com> From: David Hildenbrand Autocrypt: addr=david@redhat.com; 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charset=UTF-8; format=flowed Content-Transfer-Encoding: 7bit X-Rspamd-Server: rspam12 X-Rspam-User: X-Rspamd-Queue-Id: 13194180003 X-Stat-Signature: fpdsbb19ppfbfryh9kmhdhctw9g5r991 X-HE-Tag: 1741723376-471137 X-HE-Meta: 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 LsJmMlcT yudA/9BJQBUHQygo9K1D7sj6i+PqJVy51dYXtNyx8wN3VV1TXHCKqASKehkGFaIB5/wPUXKLL4O02H+E8t73FIKv639pnSa/m/oMZj2ZWjnBcAwl36zovZc8B3coBZDIrWH68vcMjOYsxniG5ZvTqjDt1QAJnr6JPjvjS5LtsiRv2rlXqzbXVCZAtOdQp482NKrIBV3bOnzzImeL0Fp/g1JPOanwHHRCLV8vmbM5KWlb6LQ+nO5CRt4EtGVDglXjw9lfWoEZBDMFCj6RAm06CnF1L7bW1DStbB7OL41eKZ/absDdY47KhM7K51cjclR3d12xCSUGW5GsO+LyTXMn4C+XZN48IKHpev5GopkH2CkCXbMcjMpjxST3WW8C+WhLerCxpOksq4V9bPvljyFGL7AocOFj8jZUA7/fUbNUseXx9zcfqhLTjnIuTh02B73YDV3TK 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 11.03.25 13:32, Oleg Nesterov wrote: > On 03/11, David Hildenbrand wrote: >> >> Regarding both questions, the code is fairly racy. Nothing would stop user >> space from (a) modifying that memory > > Yes, but we don't really care. uprobes.c assumes that user-space won't play > with the probed memory. Right, I primarily care about that if user space would do it, that we don't trigger unintended behavior (e.g., overwriting pagecache pages etc, WARN etc). Likely the re-validating the page content is indeed something we can drop. > > Note that if is_register is false, then vma can be even writable. Hmm, why? > Perhaps valid_vma() should ignore is_register and nack VM_MAYWRITE ? But > this doesn't really matter, say, gdb can change this memory anyway. Again, > we don't really care. > >>> do something like >>> >>> /* Walk the page tables again, to perform the actual update. */ >>> ret = -EAGAIN; >>> folio = folio_walk_start(&fw, vma, vaddr, 0); >>> if (folio) { >>> if (fw.page == page) { >>> WARN_ON(is_register && !folio_test_anon(folio)); >> >> Yes, that would work (we could leave the WARN_ON in __uprobe_write_opcode), >> but I am not sure if the end result is better better. No strong opinion on >> the details though. > > Will, this way __uprobe_write_opcode() will look a little bit simpler... > > But I won't insist, please do what you think is better. I'll take another look at this series probably next week (I'm on PTO this week) to then resend once adjusted + retested. Thanks! -- Cheers, David / dhildenb