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

[Greg KH <gregkh@linuxfoundation.org>]

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 <ardb@kernel.org>
> > 
> > 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 <ardb@kernel.org>
> > Cc: Anshuman Khandual <anshuman.khandual@arm.com>
> > Cc: Will Deacon <will@kernel.org>
> > Cc: Steven Price <steven.price@arm.com>
> > Cc: Robin Murphy <robin.murphy@arm.com>
> > Link: https://lore.kernel.org/r/20201014081857.3288-1-ardb@kernel.org
> > Signed-off-by: Catalin Marinas <catalin.marinas@arm.com>
> > Signed-off-by: Florian Fainelli <florian.fainelli@broadcom.com>
> 
> 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