Date: Thu, 18 Jan 2018 08:49:31 -0800 From: Linus Torvalds <torvalds@...ux-foundation.org> To: Christoph Hellwig <hch@...radead.org> Cc: Alan Cox <alan@...ux.intel.com>, Eric Dumazet <edumazet@...gle.com>, Dan Williams <dan.j.williams@...el.com>, Linux Kernel Mailing List <linux-kernel@...r.kernel.org>, linux-arch@...r.kernel.org, Andi Kleen <ak@...ux.intel.com>, Kees Cook <keescook@...omium.org>, kernel-hardening@...ts.openwall.com, Greg Kroah-Hartman <gregkh@...uxfoundation.org>, "the arch/x86 maintainers" <x86@...nel.org>, Ingo Molnar <mingo@...hat.com>, Al Viro <viro@...iv.linux.org.uk>, "H. Peter Anvin" <hpa@...or.com>, Thomas Gleixner <tglx@...utronix.de>, Andrew Morton <akpm@...ux-foundation.org> Subject: Re: [PATCH v3 8/9] x86: use __uaccess_begin_nospec and ASM_IFENCE in get_user paths On Thu, Jan 18, 2018 at 8:38 AM, Christoph Hellwig <hch@...radead.org> wrote: > > > But there are about ~100 set_fs() calls in generic code, and some of > > those really are pretty fundamental. Doing things like "kernel_read()" > > without set_fs() is basically impossible. > > Not if we move to iov_iter or iov_iter-like behavior for all reads > and writes. Not going to happen. Really. We have how many tens of thousands of drivers again, all doing "copy_to_user()". And the fact is, set_fs() really isn't even a problem for this. Never really has been. From a security standpoint, it would actually be *much* worse if we made those ten thousand places do "if (kernel_flag) memcpy() else copy_to_user()". We've had some issues with set_fs() being abused in interesting ways. But "kernel_read()" and friends is not it. Linus
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