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

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Message-ID: <62786457-d4a1-4861-8bec-7e478626f4db@broadcom.com>
Date: Thu, 9 Jan 2025 09:01:13 -0800
From: Florian Fainelli <florian.fainelli@...adcom.com>
To: stable@...r.kernel.org
Cc: Ard Biesheuvel <ardb@...nel.org>,
 Anshuman Khandual <anshuman.khandual@....com>, Will Deacon
 <will@...nel.org>, Steven Price <steven.price@....com>,
 Robin Murphy <robin.murphy@....com>,
 Catalin Marinas <catalin.marinas@....com>, Baruch Siach <baruch@...s.co.il>,
 Petr Tesarik <ptesarik@...e.com>, Mark Rutland <mark.rutland@....com>,
 Joey Gouly <joey.gouly@....com>, "Mike Rapoport (IBM)" <rppt@...nel.org>,
 Yang Shi <yang@...amperecomputing.com>,
 "moderated list:ARM64 PORT (AARCH64 ARCHITECTURE)"
 <linux-arm-kernel@...ts.infradead.org>,
 open list <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH] arm64: mm: account for hotplug memory when randomizing
 the linear region

On 1/9/25 08:54, Florian Fainelli wrote:
> From: Ard Biesheuvel <ardb@...nel.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@...nel.org>
> Cc: Anshuman Khandual <anshuman.khandual@....com>
> Cc: Will Deacon <will@...nel.org>
> Cc: Steven Price <steven.price@....com>
> Cc: Robin Murphy <robin.murphy@....com>
> Link: https://lore.kernel.org/r/20201014081857.3288-1-ardb@kernel.org
> Signed-off-by: Catalin Marinas <catalin.marinas@....com>
> Signed-off-by: Florian Fainelli <florian.fainelli@...adcom.com>

Forgot to update the patch subject, but this one is for 5.10.
-- 
Florian