Date: Mon, 8 May 2017 16:02:30 +0200 From: Ingo Molnar <mingo@...nel.org> To: Kees Cook <keescook@...omium.org> Cc: Thomas Garnier <thgarnie@...gle.com>, 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: [PATCH v9 1/4] syscalls: Verify address limit before returning to user-mode * Kees Cook <keescook@...omium.org> wrote: > > And yes, I realize that there were other such bugs and that such bugs might > > occur in the future - but why not push the overhead of the security check to > > the kernel build phase? I.e. I'm wondering how well we could do static > > analysis during kernel build - would a limited mode of Sparse be good enough > > for that? Or we could add a new static checker to tools/, built from first > > principles and used primarily for extended syntactical checking. > > Static analysis is just not going to cover all cases. We've had vulnerabilities > where interrupt handlers left KERNEL_DS set, for example. [...] Got any commit ID of that bug - was it because a function executed by the interrupt handler leaked KERNEL_DS? > [...] If there are performance concerns, let's put this behind a CONFIG. 2-5 > instructions is not an issue for most people that want this coverage. That doesn't really _solve_ the performance concerns, it just forces most people to enable it by creating a 'security or performance' false dichotomy ... > [...] and it still won't catch everything. Bug-finding is different from making > a bug class just unexploitable at all. As we've done before, it's the difference > between trying to find format string attacks vs just removing %n from the format > parser. No, it does not make it unexploitable, it could still be exploitable if the runtime check is buggy or if there's kernel execution outside of the regular system call paths - there's plenty of such hardware functionality on x86 for example. Thanks, Ingo
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