Date: Mon, 8 May 2017 12:51:34 -0700 From: Thomas Garnier <thgarnie@...gle.com> To: Kees Cook <keescook@...omium.org> Cc: Daniel Micay <danielmicay@...il.com>, Ingo Molnar <mingo@...nel.org>, Martin Schwidefsky <schwidefsky@...ibm.com>, Heiko Carstens <heiko.carstens@...ibm.com>, Dave Hansen <dave.hansen@...el.com>, Arnd Bergmann <arnd@...db.de>, Thomas Gleixner <tglx@...utronix.de>, David Howells <dhowells@...hat.com>, René Nyffenegger <mail@...enyffenegger.ch>, Andrew Morton <akpm@...ux-foundation.org>, "Paul E . McKenney" <paulmck@...ux.vnet.ibm.com>, "Eric W . Biederman" <ebiederm@...ssion.com>, Oleg Nesterov <oleg@...hat.com>, Pavel Tikhomirov <ptikhomirov@...tuozzo.com>, Ingo Molnar <mingo@...hat.com>, "H . Peter Anvin" <hpa@...or.com>, Andy Lutomirski <luto@...nel.org>, Paolo Bonzini <pbonzini@...hat.com>, Rik van Riel <riel@...hat.com>, Josh Poimboeuf <jpoimboe@...hat.com>, Borislav Petkov <bp@...en8.de>, Brian Gerst <brgerst@...il.com>, "Kirill A . Shutemov" <kirill.shutemov@...ux.intel.com>, Christian Borntraeger <borntraeger@...ibm.com>, Russell King <linux@...linux.org.uk>, Will Deacon <will.deacon@....com>, Catalin Marinas <catalin.marinas@....com>, Mark Rutland <mark.rutland@....com>, James Morse <james.morse@....com>, linux-s390 <linux-s390@...r.kernel.org>, LKML <linux-kernel@...r.kernel.org>, Linux API <linux-api@...r.kernel.org>, "the arch/x86 maintainers" <x86@...nel.org>, "linux-arm-kernel@...ts.infradead.org" <linux-arm-kernel@...ts.infradead.org>, Kernel Hardening <kernel-hardening@...ts.openwall.com>, Linus Torvalds <torvalds@...ux-foundation.org>, Peter Zijlstra <a.p.zijlstra@...llo.nl> Subject: Re: Re: [PATCH v9 1/4] syscalls: Verify address limit before returning to user-mode On Mon, May 8, 2017 at 8:26 AM, Kees Cook <keescook@...omium.org> wrote: > On Mon, May 8, 2017 at 8:22 AM, Daniel Micay <danielmicay@...il.com> wrote: >> On Mon, 2017-05-08 at 09:52 +0200, Ingo Molnar wrote: >>> >>> ... it's just not usable in that form for a regular maintenance flow. >>> >>> So what would be more useful is to add a specific Sparse check that >>> only checks >>> KERNEL_DS, to add it as a regular (.config driven) build option and >>> make sure the >>> kernel build has zero warnings. >>> >>> From that point on we can declare that this kind of bug won't occur >>> anymore, if >>> the Sparse implementation of the check is correct. >>> >>> But there's a (big) problem with that development model: Sparse is not >>> part of the >>> kernel tree and adding a feature to it while making the kernel depend >>> on that >>> brand new feature is a logistical nightmare. The overhead is quite >>> similar to >>> adding new features to a compiler - it happens at a glacial pace and >>> is only done >>> for major features really, at considerable expense. I don't think this >>> is an >>> adequate model for 'extended syntax checking' of the kernel, >>> especially when it >>> comes to correctness that has such obvious security impact. >>> >>> Thanks, >>> >>> Ingo >> >> There's the option of using GCC plugins now that the infrastructure was >> upstreamed from grsecurity. It can be used as part of the regular build >> process and as long as the analysis is pretty simple it shouldn't hurt >> compile time much. > > Well, and that the situation may arise due to memory corruption, not > from poorly-matched set_fs() calls, which static analysis won't help > solve. We need to catch this bad kernel state because it is a very bad > state to run in. Of course, I agree with Kees points on this and previous emails. A static analysis solution is hard to scale across functions and build time can suffer. I don't think the coverage will be good enough to consider this change and static analysis as similar. > > -Kees > > -- > Kees Cook > Pixel Security -- Thomas
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