linux-kernel - Re: [PATCH 2/3] Refactor hypercall infrastructure

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: Windows password security audit tool. GUI, reports in PDF.

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

Date:	Wed, 29 Aug 2007 04:12:57 +1000
From:	Rusty Russell <rusty@...tcorp.com.au>
To:	Anthony Liguori <aliguori@...ibm.com>
Cc:	kvm-devel@...ts.sourceforge.net, Avi Kivity <avi@...ranet.com>,
	Ingo Molnar <mingo@...e.hu>, Dor Laor <dor.laor@...ranet.com>,
	linux-kernel@...r.kernel.org
Subject: Re: [PATCH 2/3] Refactor hypercall infrastructure

On Mon, 2007-08-27 at 10:16 -0500, Anthony Liguori wrote:
> This patch refactors the current hypercall infrastructure to better support live
> migration and SMP.  It eliminates the hypercall page by trapping the UD
> exception that would occur if you used the wrong hypercall instruction for the
> underlying architecture and replacing it with the right one lazily.

It also reduces the number of hypercall args, which you don't mention
here.
	
> +	er = emulate_instruction(&svm->vcpu, kvm_run, 0, 0);
> +
> +	/* we should only succeed here in the case of hypercalls which
> +	   cannot generate an MMIO event.  MMIO means that the emulator
> +	   is mistakenly allowing an instruction that should generate
> +	   a UD fault so it's a bug. */
> +	BUG_ON(er == EMULATE_DO_MMIO);

This seems... unwise.  Firstly we know our emulator is incomplete.
Secondly an SMP guest can exploit this to crash the host.

(Code is in two places).

> +#define KVM_HYPERCALL ".byte 0x0f,0x01,0xc1"

A nice big comment would be nice here, I think.  Note that this is big
enough for both "int $0x1f" and "sysenter", so I'm happy.

Cheers,
Rusty.

-
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/