Date: Mon, 8 May 2017 15:23:59 +0200 From: Daniel Gruss <daniel.gruss@...k.tugraz.at> To: Thomas Garnier <thgarnie@...gle.com> CC: kernel list <linux-kernel@...r.kernel.org>, Kernel Hardening <kernel-hardening@...ts.openwall.com>, "clementine.maurice@...k.tugraz.at" <clementine.maurice@...k.tugraz.at>, "moritz.lipp@...k.tugraz.at" <moritz.lipp@...k.tugraz.at>, Michael Schwarz <michael.schwarz@...k.tugraz.at>, Richard Fellner <richard.fellner@...dent.tugraz.at>, "Kirill A. Shutemov" <kirill.shutemov@...ux.intel.com>, Ingo Molnar <mingo@...nel.org>, "anders.fogh@...ta-adan.de" <anders.fogh@...ta-adan.de> Subject: Re: [RFC, PATCH] x86_64: KAISER - do not map kernel in user mode On 05.05.2017 10:23, Daniel Gruss wrote: >> - How this approach prevent the hardware attacks you mentioned? You >> still have to keep a part of _text in the pagetable and an attacker >> could discover it no? (and deduce the kernel base address). > > These parts are moved to a different section (.user_mapped) which is at a possibly predictable location - the location > of the randomized parts of the kernel is independent of the location of .user_mapped. > The code/data footprint for .user_mapped is quite small, helping to reduce or eliminate the attack surface... We just discussed that in our group again: although we experimented with this part, it's not yet included in the patch. The solution we sketched is, as I wrote, we map the required (per-thread) variables in the user CR3 to a fixed location in memory. During the context switch, only this fixed part remains mapped but not the randomized pages. This is not a lot of work, because it's just mapping a few more pages and fixing a 1 or 2 lines in the context switch.
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