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Date: Fri, 2 Nov 2018 10:15:56 -0700 From: Linus Torvalds <torvalds@...ux-foundation.org> To: mst@...hat.com, Al Viro <viro@...iv.linux.org.uk> Cc: mark.rutland@....com, Kees Cook <keescook@...omium.org>, kvm@...r.kernel.org, virtualization@...ts.linux-foundation.org, netdev@...r.kernel.org, Linux Kernel Mailing List <linux-kernel@...r.kernel.org>, Andrew Morton <akpm@...ux-foundation.org>, bijan.mottahedeh@...cle.com, gedwards@....com, joe@...ches.com, lenaic@...ard.fr, liang.z.li@...el.com, mhocko@...nel.org, mhocko@...e.com, stefanha@...hat.com, wei.w.wang@...el.com, jasowang@...hat.com Subject: Re: [PULL] vhost: cleanups and fixes On Fri, Nov 2, 2018 at 10:10 AM Linus Torvalds <torvalds@...ux-foundation.org> wrote: > > Don't you take over the VM with "use_mm()" when you do the copies? So > yes, it's a kernel thread, but it has a user VM, and though that > should have the user limits. Oooh. *Just* as I sent this, I realized that "use_mm()" doesn't update the thread addr_limit. That actually looks like a bug to me - although one that you've apparently been aware of and worked around. Wouldn't it be nicer to just make "use_mm()" do set_fs(USER_DS); instead? And undo it on unuse_mm()? And, in fact, maybe we should default kernel threads to have a zero address limit, so that they can't do any user accesses at all without doing this? Adding Al to the cc, because I think he's been looking at set_fs() in general. Linus
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