linux-kernel - Re: [PATCH] arm64: kaslr: consider parange is bigger than linear_region

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Message-ID: <20250301043948.GA27296@willie-the-truck>
Date: Sat, 1 Mar 2025 04:39:50 +0000
From: Will Deacon <will@...nel.org>
To: Ard Biesheuvel <ardb@...nel.org>
Cc: Keun-O Park <kpark3469@...il.com>, linux-arm-kernel@...ts.infradead.org,
	linux-kernel@...r.kernel.org, catalin.marinas@....com,
	Keuno Park <keun-o.park@...im.com>
Subject: Re: [PATCH] arm64: kaslr: consider parange is bigger than
 linear_region_size

On Fri, Feb 28, 2025 at 02:11:41PM +0100, Ard Biesheuvel wrote:
> On Fri, 28 Feb 2025 at 06:55, Keun-O Park <kpark3469@...il.com> wrote:
> >
> > How about adding a warning message in case of linear region
> > randomization failure?
> > And, there might be two options in my mind by now to consider hotplug memory.
> > Either giving an option for users to override "parange" as kernel
> > param or providing the legacy way((memblock_end_of_DRAM() -
> > memblock_start_of_DRAM()) when CONFIG_MEMORY_HOTPLUG is off.
> > Users believe KASLR will work fine by enabling CONFIG_RANDOMIZE_BASE.
> > In case of linear region randomization failure, I think at least users
> > need to know about this failure.
> > Can you share your thoughts on this please?
> >
> 
> Randomization of the linear map has always been a best effort thing,
> so I don't think this is a big deal.
> 
> I wouldn't object to the new behavior being conditional on
> CONFIG_MEMORY_HOTPLUG, and fallback to the old behavior otherwise. But
> ultimately, it will be up to the maintainers.

Personally, given the confusion that linear map randomization seems to
cause, I'd rather reduce the number of variables on which it depends.

I also wonder whether it's actually useful at all...

Will