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Sat, 19 Sep 2020 15:23:55 -0700 (PDT) Content-Type: text/plain; charset=utf-8 Content-Transfer-Encoding: quoted-printable From: Andy Lutomirski Mime-Version: 1.0 (1.0) Subject: Re: [PATCH 1/9] kernel: add a PF_FORCE_COMPAT flag Date: Sat, 19 Sep 2020 15:23:54 -0700 Message-Id: References: <20200919220920.GI3421308@ZenIV.linux.org.uk> Cc: Christoph Hellwig , Andrew Morton , Jens Axboe , Arnd Bergmann , David Howells , linux-arm-kernel@lists.infradead.org, x86@kernel.org, linux-kernel@vger.kernel.org, linux-mips@vger.kernel.org, linux-parisc@vger.kernel.org, linuxppc-dev@lists.ozlabs.org, linux-s390@vger.kernel.org, sparclinux@vger.kernel.org, linux-block@vger.kernel.org, linux-scsi@vger.kernel.org, linux-fsdevel@vger.kernel.org, linux-aio@kvack.org, io-uring@vger.kernel.org, linux-arch@vger.kernel.org, linux-mm@kvack.org, netdev@vger.kernel.org, keyrings@vger.kernel.org, linux-security-module@vger.kernel.org In-Reply-To: <20200919220920.GI3421308@ZenIV.linux.org.uk> To: Al Viro X-Mailer: iPhone Mail (18A373) 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: > On Sep 19, 2020, at 3:09 PM, Al Viro wrote: >=20 > =EF=BB=BFOn Fri, Sep 18, 2020 at 05:16:15PM +0200, Christoph Hellwig wrote= : >>> On Fri, Sep 18, 2020 at 02:58:22PM +0100, Al Viro wrote: >>> Said that, why not provide a variant that would take an explicit >>> "is it compat" argument and use it there? And have the normal >>> one pass in_compat_syscall() to that... >>=20 >> That would help to not introduce a regression with this series yes. >> But it wouldn't fix existing bugs when io_uring is used to access >> read or write methods that use in_compat_syscall(). One example that >> I recently ran into is drivers/scsi/sg.c. >=20 > So screw such read/write methods - don't use them with io_uring. > That, BTW, is one of the reasons I'm sceptical about burying the > decisions deep into the callchain - we don't _want_ different > data layouts on read/write depending upon the 32bit vs. 64bit > caller, let alone the pointer-chasing garbage that is /dev/sg. Well, we could remove in_compat_syscall(), etc and instead have an implicit p= arameter in DEFINE_SYSCALL. Then everything would have to be explicit. Thi= s would probably be a win, although it could be quite a bit of work.=