Subject: Re: [PATCH] arm64: mm: account for hotplug memory when randomizing the linear region

From: Greg KH <[email-masked]>
Date: Sun, 12 Jan 2025 12:54:03 +0100

On Thu, Jan 09, 2025 at 09:01:13AM -0800, Florian Fainelli wrote:
> On 1/9/25 08:54, Florian Fainelli wrote:
> > From: Ard Biesheuvel <[email-masked]>
> > 
> > commit 97d6786e0669daa5c2f2d07a057f574e849dfd3e upstream
> > 
> > As a hardening measure, we currently randomize the placement of
> > physical memory inside the linear region when KASLR is in effect.
> > Since the random offset at which to place the available physical
> > memory inside the linear region is chosen early at boot, it is
> > based on the memblock description of memory, which does not cover
> > hotplug memory. The consequence of this is that the randomization
> > offset may be chosen such that any hotplugged memory located above
> > memblock_end_of_DRAM() that appears later is pushed off the end of
> > the linear region, where it cannot be accessed.
> > 
> > So let's limit this randomization of the linear region to ensure
> > that this can no longer happen, by using the CPU's addressable PA
> > range instead. As it is guaranteed that no hotpluggable memory will
> > appear that falls outside of that range, we can safely put this PA
> > range sized window anywhere in the linear region.
> > 
> > Signed-off-by: Ard Biesheuvel <[email-masked]>
> > Cc: Anshuman Khandual <[email-masked]>
> > Cc: Will Deacon <[email-masked]>
> > Cc: Steven Price <[email-masked]>
> > Cc: Robin Murphy <[email-masked]>
> > Link: https://lore.kernel.org/r/[email-masked]
> > Signed-off-by: Catalin Marinas <[email-masked]>
> > Signed-off-by: Florian Fainelli <[email-masked]>
> 
> Forgot to update the patch subject, but this one is for 5.10.

You also forgot to tell us _why_ this is needed :(

thanks,

greg k-h