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[2003:cb:c70c:cd00:c139:924e:3595:3b5]) by smtp.gmail.com with ESMTPSA id ffacd0b85a97d-37ee0b944fbsm8541274f8f.72.2024.10.23.02.13.48 (version=TLS1_3 cipher=TLS_AES_128_GCM_SHA256 bits=128/128); Wed, 23 Oct 2024 02:13:49 -0700 (PDT) Message-ID: Date: Wed, 23 Oct 2024 11:13:47 +0200 Precedence: bulk X-Mailing-List: linux-api@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 User-Agent: Mozilla Thunderbird Subject: Re: [PATCH v2 0/5] implement lightweight guard pages To: Vlastimil Babka , Dmitry Vyukov , Lorenzo Stoakes Cc: fw@deneb.enyo.de, 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, 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, willy@infradead.org, elver@google.com, Linus Torvalds References: <87a5eysmj1.fsf@mid.deneb.enyo.de> <20241023062417.3862170-1-dvyukov@google.com> <8471d7b1-576b-41a6-91fb-1c9baae8c540@redhat.com> <5a3d3bc8-60db-46d0-b689-9aeabcdb8eab@lucifer.local> From: David Hildenbrand Content-Language: en-US Autocrypt: addr=david@redhat.com; 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charset=UTF-8; format=flowed Content-Transfer-Encoding: 7bit On 23.10.24 11:06, Vlastimil Babka wrote: > On 10/23/24 10:56, Dmitry Vyukov wrote: >>> >>> Overall while I sympathise with this, it feels dangerous and a pretty major >>> change, because there'll be something somewhere that will break because it >>> expects faults to be swallowed that we no longer do swallow. >>> >>> So I'd say it'd be something we should defer, but of course it's a highly >>> user-facing change so how easy that would be I don't know. >>> >>> But I definitely don't think a 'introduce the ability to do cheap PROT_NONE >>> guards' series is the place to also fundmentally change how user access >>> page faults are handled within the kernel :) >> >> Will delivering signals on kernel access be a backwards compatible >> change? Or will we need a different API? MADV_GUARD_POISON_KERNEL? >> It's just somewhat painful to detect/update all userspace if we add >> this feature in future. Can we say signal delivery on kernel accesses >> is unspecified? > > Would adding signal delivery to guard PTEs only help enough the ASAN etc > usecase? Wouldn't it be instead possible to add some prctl to opt-in the > whole ASANized process to deliver all existing segfaults as signals instead > of -EFAULT ? Not sure if it is an "instead", you might have to deliver the signal in addition to letting the syscall fail (not that I would be an expert on signal delivery :D ). prctl sounds better, or some way to configure the behavior on VMA ranges; otherwise we would need yet another marker, which is not the end of the world but would make it slightly more confusing. -- Cheers, David / dhildenb