From mboxrd@z Thu Jan 1 00:00:00 1970 From: Alan Cox Subject: Re: [PATCH 06/18] x86, barrier: stop speculation for failed access_ok Date: Sat, 6 Jan 2018 12:32:42 +0000 Message-ID: <20180106123242.77f4d860@alans-desktop> References: <151520099201.32271.4677179499894422956.stgit@dwillia2-desk3.amr.corp.intel.com> <151520102670.32271.8447983009852138826.stgit@dwillia2-desk3.amr.corp.intel.com> Mime-Version: 1.0 Content-Type: text/plain; charset=US-ASCII Content-Transfer-Encoding: 7bit Cc: Dan Williams , Linux Kernel Mailing List , linux-arch@vger.kernel.org, Andi Kleen , Arnd Bergmann , Greg Kroah-Hartman , Peter Zijlstra , Network Development , "the arch/x86 maintainers" , Ingo Molnar , "H. Peter Anvin" , Thomas Gleixner To: Linus Torvalds Return-path: In-Reply-To: Sender: linux-arch-owner@vger.kernel.org List-Id: netdev.vger.kernel.org On Fri, 5 Jan 2018 18:52:07 -0800 Linus Torvalds wrote: > On Fri, Jan 5, 2018 at 5:10 PM, Dan Williams wrote: > > From: Andi Kleen > > > > When access_ok fails we should always stop speculating. > > Add the required barriers to the x86 access_ok macro. > > Honestly, this seems completely bogus. Also for x86-64 if we are trusting that an AND with a constant won't get speculated into something else surely we can just and the address with ~(1 << 63) before copying from/to user space ? The user will then just speculatively steal their own memory. Alan