linux-kernel - Re: [PATCH 0/3] Remove interrupt stack table usage from x86

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Message-ID: <49578896.8030703@redhat.com>
Date:	Sun, 28 Dec 2008 16:09:26 +0200
From:	Avi Kivity <avi@...hat.com>
To:	Andi Kleen <andi@...stfloor.org>
CC:	x86@...nel.org, Ingo Molnar <mingo@...e.hu>,
	linux-kernel <linux-kernel@...r.kernel.org>,
	KVM list <kvm@...r.kernel.org>
Subject: Re: [PATCH 0/3] Remove interrupt stack table usage from x86_64 kernel

(restoring cc list)

Andi Kleen wrote:
> One of the other problems: NMIs and MCEs have the same problem with SYSCALL
>   

This one however looks unsolvable.  Userspace can point %rsp into 
arbitrary memory, issue a syscall, and hope for an nmi.  Since we're in 
cpl 0 and are not using IST, the processor will not switch stacks, and 
the nmi stack frame will corrupt any memory the user chooses to point to.

Even without a malicious user, %rsp could legitimately point at unmapped 
memory.

I don't see how syscall could work on i386, and indeed:

> vdso32.so-$(VDSO32-y)        += int80
> vdso32.so-$(CONFIG_COMPAT)    += syscall
> vdso32.so-$(VDSO32-y)        += sysenter

It's disabled.  Is that the reason?

-- 
error compiling committee.c: too many arguments to function

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