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[2003:cb:c70c:cd00:c139:924e:3595:3b5]) by smtp.gmail.com with ESMTPSA id ffacd0b85a97d-37ee0a37d25sm8269356f8f.23.2024.10.23.00.19.03 (version=TLS1_3 cipher=TLS_AES_128_GCM_SHA256 bits=128/128); Wed, 23 Oct 2024 00:19:05 -0700 (PDT) Message-ID: <8471d7b1-576b-41a6-91fb-1c9baae8c540@redhat.com> Date: Wed, 23 Oct 2024 09:19:03 +0200 MIME-Version: 1.0 User-Agent: Mozilla Thunderbird Subject: Re: [PATCH v2 0/5] implement lightweight guard pages To: Dmitry Vyukov , fw@deneb.enyo.de Cc: James.Bottomley@HansenPartnership.com, Liam.Howlett@oracle.com, akpm@linux-foundation.org, arnd@arndb.de, brauner@kernel.org, chris@zankel.net, deller@gmx.de, hch@infradead.org, ink@jurassic.park.msu.ru, jannh@google.com, jcmvbkbc@gmail.com, jeffxu@chromium.org, jhubbard@nvidia.com, linux-alpha@vger.kernel.org, linux-api@vger.kernel.org, linux-arch@vger.kernel.org, linux-kernel@vger.kernel.org, linux-kselftest@vger.kernel.org, linux-mips@vger.kernel.org, linux-mm@kvack.org, linux-parisc@vger.kernel.org, lorenzo.stoakes@oracle.com, mattst88@gmail.com, muchun.song@linux.dev, paulmck@kernel.org, richard.henderson@linaro.org, shuah@kernel.org, sidhartha.kumar@oracle.com, surenb@google.com, tsbogend@alpha.franken.de, vbabka@suse.cz, willy@infradead.org, elver@google.com References: <87a5eysmj1.fsf@mid.deneb.enyo.de> <20241023062417.3862170-1-dvyukov@google.com> From: David Hildenbrand Autocrypt: addr=david@redhat.com; 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charset=UTF-8; format=flowed Content-Transfer-Encoding: 7bit X-Stat-Signature: ob511icq3ad75s9i7owus9gmje7j5fam X-Rspamd-Queue-Id: 7AF161C0012 X-Rspam-User: X-Rspamd-Server: rspam10 X-HE-Tag: 1729667917-761591 X-HE-Meta: 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 Y7GC/3ff gfMcq77ytiN6qrlXF5iU4W5IcYodstCnvWv7SOPEmdIBdqO3lZADanWfVFg1325tBELYwgIXuJd7mmYNnZILbmRb3FpvoCzCKeFN+V10mM4IcXN/byxWPuYqsOiMrmBt1R3ePvhyJompmDf/ffcq0oTQ7SXvd4X2xjBr2RZlJT0c9zCeVW4dC6impUrZ0I8BTBlpP2C1IFxF82aHX3vmISUQdHxH8kV6wBMB/yDWilDfBuQ5V5rggsC215xyUG09xbtlUE8FhddQk1aixzENcRh9pg+qVsUlf9iRCI8splEgq4UmLryYzi7hJ5opSjC9v+WSmpol/Kjz0JkSBdr7IxHhAUp/FRB7HbDoHW25MX7Q3E+joGf3b2SEVcZduC+7fDsmylpx/geTI6nU= X-Bogosity: Ham, tests=bogofilter, spamicity=0.000224, 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 23.10.24 08:24, Dmitry Vyukov wrote: > Hi Florian, Lorenzo, > > This looks great! > > What I am VERY interested in is if poisoned pages cause SIGSEGV even when > the access happens in the kernel. Namely, the syscall still returns EFAULT, > but also SIGSEGV is queued on return to user-space. > > Catching bad accesses in system calls is currently the weak spot for > all user-space bug detection tools (GWP-ASan, libefence, libefency, etc). > It's almost possible with userfaultfd, but catching faults in the kernel > requires admin capability, so not really an option for generic bug > detection tools (+inconvinience of userfaultfd setup/handler). > Intercepting all EFAULT from syscalls is not generally possible > (w/o ptrace, usually not an option as well), and EFAULT does not always > mean a bug. > > Triggering SIGSEGV even in syscalls would be not just a performance > optimization, but a new useful capability that would allow it to catch > more bugs. Right, we discussed that offline also as a possible extension to the userfaultfd SIGBUS mode. I did not look into that yet, but I was wonder if there could be cases where a different process could trigger that SIGSEGV, and how to (and if to) handle that. For example, ptrace (access_remote_vm()) -> GUP likely can trigger that. I think with userfaultfd() we will currently return -EFAULT, because we call get_user_page_vma_remote() that is not prepared for dropping the mmap lock. Possibly that is the right thing to do, but not sure :) These "remote" faults set FOLL_REMOTE -> FAULT_FLAG_REMOTE, so we might be able to distinguish them and perform different handling. -- Cheers, David / dhildenb