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Date: Mon, 22 Jun 2020 15:15:18 -0600
From: "Jason A. Donenfeld" <Jason@...c4.com>
To: Ard Biesheuvel <ardb@...nel.org>
Cc: linux-arm-kernel <linux-arm-kernel@...ts.infradead.org>,
ACPI Devel Maling List <linux-acpi@...r.kernel.org>, Will Deacon <will@...nel.org>,
Catalin Marinas <catalin.marinas@....com>, lorenzo.pieralisi@....com, sudeep.holla@....com,
Kernel Hardening <kernel-hardening@...ts.openwall.com>
Subject: Re: [RFC PATCH] arm64/acpi: disallow AML memory opregions to access
kernel memory
Hmm, actually...
> > if (memblock_is_map_memory(phys))
> > - return (void __iomem *)__phys_to_virt(phys);
> > + return NULL;
It might be prudent to have this check take into account the size of
the region being mapped. I realize ACPI considers it to be undefined
if you cross borders, but I could imagine actual system behavior being
somewhat complicated, and a clever bypass being possible.
Hypothetically: KASLR starts kernel at phys_base+offset, [phys_base,
rounddownpage(offset)) doesn't get mapped, malicious acpi then maps
phys_base+rounddownpage(offset)-1, and then this check doesn't get
hit.
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