linux-kernel - Re: [PATCH] KVM: x86: zero IDT limit on entry to SMM

lists.openwall.net		lists / announce owl-users owl-dev john-users john-dev passwdqc-users yescrypt popa3d-users / oss-security kernel-hardening musl sabotage tlsify passwords / crypt-dev xvendor / Bugtraq Full-Disclosure linux-kernel linux-netdev linux-ext4 linux-hardening linux-cve-announce PHC
Open Source and information security mailing list archives

Hash Suite for Android: free password hash cracker in your pocket

[<prev] [next>] [<thread-prev] [day] [month] [year] [list]

Date:	Mon, 10 Aug 2015 17:31:17 +0200
From:	Radim Krčmář <rkrcmar@...hat.com>
To:	Paolo Bonzini <pbonzini@...hat.com>
Cc:	linux-kernel@...r.kernel.org, kvm@...r.kernel.org,
	dgilbert@...hat.com
Subject: Re: [PATCH] KVM: x86: zero IDT limit on entry to SMM

2015-08-07 12:54+0200, Paolo Bonzini:
> The recent BlackHat 2015 presentation "The Memory Sinkhole"
> mentions that the IDT limit is zeroed on entry to SMM.

Slide 64 of
https://www.blackhat.com/docs/us-15/materials/us-15-Domas-The-Memory-Sinkhole-Unleashing-An-x86-Design-Flaw-Allowing-Universal-Privilege-Escalation.pdf

> This is not documented, and must have changed some time after 2010
> (see http://www.ssi.gouv.fr/uploads/IMG/pdf/IT_Defense_2010_final.pdf).
> KVM was not doing it, but the fix is easy.

This patch also clears the IDT base.  Fetching original IDT is better
done from SMM saved state (and an anti-exploit based on comparing those
two seems unlikely) so it should be fine,

Reviewed-by: Radim Krčmář <rkrcmar@...hat.com>

> Signed-off-by: Paolo Bonzini <pbonzini@...hat.com>
> ---

That takes care of Attack 1.
KVM is likely not vulnerable to attack 2 and 3 because of an emergent
security feature.  (A simple modification of kvm-unit-tests show that
mapping APIC base on top of real code/data makes the APIC page hidden
and I expect SMM memslot to behave similarly.)
--
To unsubscribe from this list: send the line "unsubscribe linux-kernel" in
the body of a message to majordomo@...r.kernel.org
More majordomo info at  http://vger.kernel.org/majordomo-info.html
Please read the FAQ at  http://www.tux.org/lkml/