linux-kernel - Re: [PATCH v3 1/1] x86/boot/compressed: Fix avoiding memmap in physical KASLR

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Message-ID: <CAAi7L5dMxpS_zvPviNH+id41bXD2NOHeUGF-Gfp_AN6J9nJP2g@mail.gmail.com>
Date: Tue, 13 Jan 2026 12:21:25 +0100
From: Michał Cłapiński <mclapinski@...gle.com>
To: Borislav Petkov <bp@...en8.de>
Cc: Dave Hansen <dave.hansen@...el.com>, Ard Biesheuvel <ardb@...nel.org>, 
	Thomas Gleixner <tglx@...utronix.de>, Ingo Molnar <mingo@...hat.com>, 
	Dave Hansen <dave.hansen@...ux.intel.com>, Chris Li <chrisl@...nel.org>, x86@...nel.org, 
	"H. Peter Anvin" <hpa@...or.com>, Dan Williams <dan.j.williams@...el.com>, 
	Pasha Tatashin <pasha.tatashin@...een.com>, linux-kernel@...r.kernel.org
Subject: Re: [PATCH v3 1/1] x86/boot/compressed: Fix avoiding memmap in
 physical KASLR

On Mon, Jan 12, 2026 at 10:39 PM Borislav Petkov <bp@...en8.de> wrote:
>
> On Mon, Dec 29, 2025 at 03:25:12PM +0100, Michał Cłapiński wrote:
> > I'm not in a hurry. What I meant is I understand that Ard's change
> > would also fix the issue but it's a bigger change with a higher chance
> > of being rolled back.
>
> Why is that so?
>
> Ard's change is simply dropping those cmdline params which are conflicting
> anyway.

Currently, if you have 4 or fewer memmaps, KASLR correctly avoids
putting the kernel there. That just works now and Ard's change would
disable that.

> So why is there even a risk to be reverted?

Not because I expect something to break. You want to disable a
security measure that works currently (up to 4 memmaps). Some security
engineer might see this in rc1 and request a revert. My change doesn't
disable a security measure so I don't expect it to be reverted.

> > What should I do now? Should I change something in the code? Should I just
> > wait?
>
> I think we should merge Ard's change directly and be done with it.
>
> Unless I'm missing an angle...?

I'd be okay with that too (assuming it's not reverted).