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Sun, 20 Sep 2020 12:15:02 -0700 (PDT) X-Gm-Message-State: AOAM531WbuIujAtx+SH8JYClwe4a7wf0C4tldEV3HiGIyfdGtQmG4x6D CJ712eEXWmc+29EM/vXm4bkbld/KCXnPFv0wxIfYwg== X-Google-Smtp-Source: ABdhPJznW7DCp463LJOKwLIqH+/ZeaOskntfIIXR0IAAA+ZM4omIXer1gN2IBUUGrBDkxuviLF20WI9Nmbt3oWZvbk0= X-Received: by 2002:a05:600c:2183:: with SMTP id e3mr27891946wme.49.1600629301119; Sun, 20 Sep 2020 12:15:01 -0700 (PDT) MIME-Version: 1.0 References: <20200918124533.3487701-1-hch@lst.de> <20200918124533.3487701-2-hch@lst.de> <20200920151510.GS32101@casper.infradead.org> <20200920180742.GN3421308@ZenIV.linux.org.uk> In-Reply-To: <20200920180742.GN3421308@ZenIV.linux.org.uk> From: Andy Lutomirski Date: Sun, 20 Sep 2020 12:14:49 -0700 X-Gmail-Original-Message-ID: Message-ID: Subject: Re: [PATCH 1/9] kernel: add a PF_FORCE_COMPAT flag To: Al Viro X-CRM114-Version: 20100106-BlameMichelson ( TRE 0.8.0 (BSD) ) MR-646709E3 X-CRM114-CacheID: sfid-20200920_151504_238110_C869DDEA X-CRM114-Status: GOOD ( 27.40 ) X-BeenThere: linux-arm-kernel@lists.infradead.org X-Mailman-Version: 2.1.29 Precedence: list List-Id: List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , Cc: linux-aio , "open list:MIPS" , David Howells , Linux-MM , keyrings@vger.kernel.org, sparclinux , Christoph Hellwig , linux-arch , linux-s390 , Linux SCSI List , X86 ML , Matthew Wilcox , Arnd Bergmann , linux-block , io-uring@vger.kernel.org, linux-arm-kernel , Jens Axboe , Parisc List , Network Development , LKML , LSM List , Linux FS Devel , Andrew Morton , linuxppc-dev Content-Type: text/plain; charset="us-ascii" Content-Transfer-Encoding: 7bit Sender: "linux-arm-kernel" Errors-To: linux-arm-kernel-bounces+linux-arm-kernel=archiver.kernel.org@lists.infradead.org On Sun, Sep 20, 2020 at 11:07 AM Al Viro wrote: > > On Sun, Sep 20, 2020 at 04:15:10PM +0100, Matthew Wilcox wrote: > > On Fri, Sep 18, 2020 at 02:45:25PM +0200, Christoph Hellwig wrote: > > > Add a flag to force processing a syscall as a compat syscall. This is > > > required so that in_compat_syscall() works for I/O submitted by io_uring > > > helper threads on behalf of compat syscalls. > > > > Al doesn't like this much, but my suggestion is to introduce two new > > opcodes -- IORING_OP_READV32 and IORING_OP_WRITEV32. The compat code > > can translate IORING_OP_READV to IORING_OP_READV32 and then the core > > code can know what that user pointer is pointing to. > > Let's separate two issues: > 1) compat syscalls want 32bit iovecs. Nothing to do with the > drivers, dealt with just fine. > 2) a few drivers are really fucked in head. They use different > *DATA* layouts for reads/writes, depending upon the calling process. > IOW, if you fork/exec a 32bit binary and your stdin is one of those, > reads from stdin in parent and child will yield different data layouts. > On the same struct file. > That's what Christoph worries about (/dev/sg he'd mentioned is > one of those). > > IMO we should simply have that dozen or so of pathological files > marked with FMODE_SHITTY_ABI; it's not about how they'd been opened - > it describes the userland ABI provided by those. And it's cast in stone. > I wonder if this is really quite cast in stone. We could also have FMODE_SHITTY_COMPAT and set that when a file like this is *opened* in compat mode. Then that particular struct file would be read and written using the compat data format. The change would be user-visible, but the user that would see it would be very strange indeed. I don't have a strong opinion as to whether that is better or worse than denying io_uring access to these things, but at least it moves the special case out of io_uring. --Andy _______________________________________________ linux-arm-kernel mailing list linux-arm-kernel@lists.infradead.org http://lists.infradead.org/mailman/listinfo/linux-arm-kernel