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[198.145.64.163]) by smtp.gmail.com with ESMTPSA id q12-20020a170902eb8c00b0016dbe37cebdsm6230493plg.246.2022.09.23.14.19.43 (version=TLS1_3 cipher=TLS_AES_256_GCM_SHA384 bits=256/256); Fri, 23 Sep 2022 14:19:43 -0700 (PDT) Date: Fri, 23 Sep 2022 14:19:43 -0700 From: Kees Cook To: Ard Biesheuvel Cc: Guenter Roeck , Peter Zijlstra , Dave Hansen , linux-kernel@vger.kernel.org, Darren Hart , Andy Shevchenko , Thomas Gleixner , Ingo Molnar , Borislav Petkov , x86@kernel.org, linux-efi@vger.kernel.org, "H. Peter Anvin" Subject: Re: [PATCH] x86/mm+efi: Avoid creating W+X mappings Message-ID: <202209231417.F73F40060@keescook> References: <08906193-246b-c874-8bac-1d98d2313ac4@roeck-us.net> <20220922193157.1673623-1-dave.hansen@linux.intel.com> <5f443915-b38a-c78d-cccd-876501434cef@roeck-us.net> <202209231126.6855D54@keescook> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On Fri, Sep 23, 2022 at 09:53:02PM +0200, Ard Biesheuvel wrote: > On Fri, 23 Sept 2022 at 20:31, Kees Cook wrote: > > > > On Fri, Sep 23, 2022 at 04:26:58PM +0200, Ard Biesheuvel wrote: > > > I was basically making the point that we still support i386 without > > > PAE (which is a prerequisite for supporting non-executable mappings), > > > and if we are going to be pedantic about security on this > > > architecture, we should probably make PAE mandatory as well. > > > > My expectation would be that if someone is running modern kernels on i386, > > they're not using PAE. If they care about PAE, I'd expect them to have > > long since moved to x86_64. > > > > Not sure I follow. If they care about PAE, they turn it on. Or do you > mean 'if they care about being able to address lots of physical > memory'? Because the *other* reason you might care about PAE is > because it gives you NX support. Right, I meant if they care about NX (and the topic of this thread) they want PAE, and if they want PAE, they likely moved to x86_64 long long ago for new kernels. > But currently, PAE is not even enabled in the i386_defconfig, and > defaults to off. This means people that are unaware of this won't > enable it, and will be running without NX support. And they all make me cry. ;) > > > If we are ok with the current state, enabling this permission check on > > > i386 makes no sense. > > > > I'd agree. If it's a choice between "spend a lot of time making sure > > this works correctly on i386" and "don't do this at all on i386", I > > would pick the latter. If someone steps up to do the former, then by > > all means take the patches. > > > > OK, so it seems we're all in violent agreement here. And if there is > ever a push for enabling security features on 32-bit, we can add this > to the laundry list of things that need to be looked at. Yup. -- Kees Cook