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Date: Sat, 7 Oct 2023 00:18:24 +0200
From: Solar Designer <solar@...nwall.com>
To: Daniel Weber <daniel.weber@...pa.de>
Cc: oss-security@...ts.openwall.com, fabian.thomas@...pa.de,
lukas.gerlach@...pa.de, ruiyi.zhang@...pa.de,
Michael Schwarz <michael.schwarz@...pa.de>
Subject: Re: Meltdown-US / Meltdown 3a Remaining Leakage
Hello Daniel et al.,
Thank you very much for your research and for posting about it in here!
On Fri, Oct 06, 2023 at 12:07:17PM +0200, Daniel Weber wrote:
> we analyzed the remaining leakage of the "original" Meltdown attack
> (Meltdown-US) (1) and the variant Meltdown 3a (2). We discovered that
> the "original" Meltdown attack can be abused to infer the cache state of
> memory pages that remain mapped despite KPTI. This allows an attacker to
> monitor interrupt activity.
I assume you're talking specifically about Linux's KPTI. Let's be
naming Linux explicitly, as this list isn't only about Linux.
In Linux, /proc/interrupts is generally world-readable. So perhaps
that's something to fix first, since yes it's known to allow for
keystroke timing attacks. Should be fixed in the kernel or/and chmod'ed
by the userland. And then:
> 1) Preventing the Meltdown attack from leaking information about the
> cache state can be achieved by marking the remaining memory pages, e.g.,
> the IDT, as uncacheable. This can be achieved by using a memory-type
> range register (MTRR) or by modifying the corresponding page-table entries.
Alexander
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