linux-kernel - Re: [PATCH v4 2/4] x86/traps: Print non-canonical address on #GP

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Message-ID: <20191120213936.GM2634@zn.tnic>
Date:   Wed, 20 Nov 2019 22:39:36 +0100
From:   Borislav Petkov <bp@...en8.de>
To:     Sean Christopherson <sean.j.christopherson@...el.com>
Cc:     Jann Horn <jannh@...gle.com>, Thomas Gleixner <tglx@...utronix.de>,
        Ingo Molnar <mingo@...hat.com>,
        "H. Peter Anvin" <hpa@...or.com>, x86@...nel.org,
        Andrey Ryabinin <aryabinin@...tuozzo.com>,
        Alexander Potapenko <glider@...gle.com>,
        Dmitry Vyukov <dvyukov@...gle.com>, kasan-dev@...glegroups.com,
        linux-kernel@...r.kernel.org,
        Andrey Konovalov <andreyknvl@...gle.com>,
        Andy Lutomirski <luto@...nel.org>
Subject: Re: [PATCH v4 2/4] x86/traps: Print non-canonical address on #GP

On Wed, Nov 20, 2019 at 12:25:16PM -0800, Sean Christopherson wrote:
> I get that adding a print just for the straddle case is probably overkill,

Yes, frankly I am not too crazy about adding all that code just for the
straddle case.

Also, the straddle case is kinda clear - it is always the

  0x7ffffffffXX.. + size - 1

address and we could simply dump that address instead of dumping a
range. So we can simplify this to:

	("general protection fault, non-canonical address 0x%lx: 0000 [#1] SMP\n", addr + size - 1)

It all depends on how the access is done by the hardware but we can't
always be absolutely sure which of the non-canonical bytes was accessed
first. Depends also on the access width and yadda yadda... But I don't
think we can know for sure always without the hw telling us, thus the
"possibly" formulation.

Thx.

-- 
Regards/Gruss,
    Boris.

https://people.kernel.org/tglx/notes-about-netiquette