linux-kernel - Re: [PATCH v3 2/4] x86/traps: Print non-canonical address on #GP

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Message-ID: <CAG48ez0KscmTLf2_-tYPuoAxRjJtzUO8kmAPQ_SZTP1zvqvTtA@mail.gmail.com>
Date:   Wed, 20 Nov 2019 14:23:09 +0100
From:   Jann Horn <jannh@...gle.com>
To:     Ingo Molnar <mingo@...nel.org>
Cc:     Borislav Petkov <bp@...en8.de>,
        Thomas Gleixner <tglx@...utronix.de>,
        Ingo Molnar <mingo@...hat.com>,
        "H. Peter Anvin" <hpa@...or.com>,
        "the arch/x86 maintainers" <x86@...nel.org>,
        Andrey Ryabinin <aryabinin@...tuozzo.com>,
        Alexander Potapenko <glider@...gle.com>,
        Dmitry Vyukov <dvyukov@...gle.com>,
        kasan-dev <kasan-dev@...glegroups.com>,
        kernel list <linux-kernel@...r.kernel.org>,
        Andrey Konovalov <andreyknvl@...gle.com>,
        Andy Lutomirski <luto@...nel.org>,
        Sean Christopherson <sean.j.christopherson@...el.com>,
        Andi Kleen <ak@...ux.intel.com>
Subject: Re: [PATCH v3 2/4] x86/traps: Print non-canonical address on #GP

On Wed, Nov 20, 2019 at 2:16 PM Ingo Molnar <mingo@...nel.org> wrote:
> * Jann Horn <jannh@...gle.com> wrote:
>
> > On Wed, Nov 20, 2019 at 12:24 PM Borislav Petkov <bp@...en8.de> wrote:
> > > On Wed, Nov 20, 2019 at 12:18:59PM +0100, Ingo Molnar wrote:
> > > > How was this maximum string length of '90' derived? In what way will
> > > > that have to change if someone changes the message?
> > >
> > > That was me counting the string length in a dirty patch in a previous
> > > thread. We probably should say why we decided for a certain length and
> > > maybe have a define for it.
> >
> > Do you think something like this would be better?
> >
> > char desc[sizeof(GPFSTR) + 50 + 2*sizeof(unsigned long) + 1] = GPFSTR;
>
> I'd much prefer this for, because it's a big honking warning for people
> to not just assume things but double check the limits.

Sorry, I can't parse the start of this sentence. I _think_ you're
saying you want me to make the change to "char desc[sizeof(GPFSTR) +
50 + 2*sizeof(unsigned long) + 1]"?

> I.e. this mild obfuscation of the array size *helps* code quality in the
> long run :-)