linux-kernel - Re: [RFC PATCH 11/11] x86/boot: Move "boot heap" out of .bss

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Message-ID: <202002061331.E5956EA@keescook>
Date:   Thu, 6 Feb 2020 13:32:48 -0800
From:   Kees Cook <keescook@...omium.org>
To:     Arvind Sankar <nivedita@...m.mit.edu>
Cc:     Kristen Carlson Accardi <kristen@...ux.intel.com>,
        tglx@...utronix.de, mingo@...hat.com, bp@...en8.de, hpa@...or.com,
        arjan@...ux.intel.com, rick.p.edgecombe@...el.com, x86@...nel.org,
        linux-kernel@...r.kernel.org, kernel-hardening@...ts.openwall.com
Subject: Re: [RFC PATCH 11/11] x86/boot: Move "boot heap" out of .bss

On Thu, Feb 06, 2020 at 09:25:59AM -0500, Arvind Sankar wrote:
> On Thu, Feb 06, 2020 at 03:13:12AM -0800, Kees Cook wrote:
> > Yes, thank you for the reminder. I couldn't find the ZO_INIT_SIZE when I
> > was staring at this, since I only looked around the compressed/ directory.
> > :)
> > 
> 
> There's another thing I noticed -- you would need to ensure that the
> init_size in the header covers your boot heap even if you did split it
> out. The reason is that the bootloader will only know to reserve enough
> memory for init_size: it's possible it might put the initrd or something
> else following the kernel, or theoretically there might be reserved
> memory regions or the end of physical RAM immediately following, so you
> can't assume that area will be available when you get to extract_kernel.

Yeah, that's what I was worrying about after I wrote that patch. Yours
is the correct solution. :) (I Acked both of those now).

-- 
Kees Cook