linux-kernel - RE: [PATCH v5 02/12] array_idx: sanitize speculative array de-references

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Date:   Wed, 31 Jan 2018 14:13:45 +0000
From:   "Van De Ven, Arjan" <arjan.van.de.ven@...el.com>
To:     Ingo Molnar <mingo@...nel.org>
CC:     "Williams, Dan J" <dan.j.williams@...el.com>,
        Linus Torvalds <torvalds@...ux-foundation.org>,
        Thomas Gleixner <tglx@...utronix.de>,
        linux-arch <linux-arch@...r.kernel.org>,
        Cyril Novikov <cnovikov@...x.com>,
        Kernel Hardening <kernel-hardening@...ts.openwall.com>,
        Peter Zijlstra <peterz@...radead.org>,
        Catalin Marinas <catalin.marinas@....com>,
        X86 ML <x86@...nel.org>, Will Deacon <will.deacon@....com>,
        Russell King <linux@...linux.org.uk>,
        Ingo Molnar <mingo@...hat.com>,
        Greg KH <gregkh@...uxfoundation.org>,
        "H. Peter Anvin" <hpa@...or.com>, Alan Cox <alan@...ux.intel.com>,
        Linux Kernel Mailing List <linux-kernel@...r.kernel.org>,
        Peter Zijlstra <a.p.zijlstra@...llo.nl>
Subject: RE: [PATCH v5 02/12] array_idx: sanitize speculative array
 de-references

> > short term there was some extremely rudimentary static analysis done. clearly
> > that has extreme limitations both in insane rate of false positives, and missing
> > cases.
> 
> What was the output roughly, how many suspect places that need
> array_idx_nospec()
> handling: a few, a few dozen, a few hundred or a few thousand?
> 
> I'm guessing 'static tool emitted hundreds of sites with many false positives
> included, but the real sites are probably a few dozen' - but that's really just a
> very, very wild guess.

your guess is pretty accurate; we ended up with some 15 or so places (the first patch kit Dan mailed out)


> 
> - If it's more than a few dozen then intuitively I'd also be very much in favor of
>   compiler help: for example trickle down __user annotations that Sparse uses
> some
>   more and let the compiler sanitize indices or warn about them - without hurting
>   performance of in-kernel array handling.

we need this kind of help even if it's only for the static analysis tool


 
> Also, IMHO any tooling should very much be open source: this isn't the kind of
> bug
> that can be identified via code review, so there's no fall-back detection method
> like we have for buffer overflows.

we absolutely need some good open source tooling; my personal preference will be a compiler plugin; that way you can use all the fancy logic inside the compilers for analysis, and you can make a "I don't care just fix it" option in addition to flagging for human inspection as the kernel would.