linux-kernel - Re: [PATCH] x86_64: fixup TASK_SIZE

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Date:   Fri, 6 Mar 2020 10:09:58 -0800
From:   Andy Lutomirski <luto@...nel.org>
To:     Alexey Dobriyan <adobriyan@...il.com>
Cc:     Thomas Gleixner <tglx@...utronix.de>,
        Ingo Molnar <mingo@...hat.com>, Borislav Petkov <bp@...en8.de>,
        "H. Peter Anvin" <hpa@...or.com>, X86 ML <x86@...nel.org>,
        LKML <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH] x86_64: fixup TASK_SIZE_MAX comment

On Thu, Mar 5, 2020 at 10:17 AM Alexey Dobriyan <adobriyan@...il.com> wrote:
>
> Comment says "by preventing anything executable" which is not true.
> Even PROT_NONE mapping can't be installed at (1<<47 - 4096).
>
>         mmap(0x7ffffffff000, 4096, PROT_NONE, MAP_PRIVATE|MAP_FIXED|MAP_ANONYMOUS, -1, 0) = -1 ENOMEM

Reviewed-by: Andy Lutomirski <luto@...nel.org>

>
> I wonder if CPUs with wider address space carried the bugs...

I believe they do.  I won't swear to it.

FWIW, I specifically asked Intel to kindly fix this bug^Wfeature as
part of LA57, and I did not get a helpful response.