Re: [PATCH][GIT PULL][v3.3] x86: Test saved %rip in NMI to determinenested NMI

[H. Peter Anvin]

On 02/19/2012 12:34 PM, Steven Rostedt wrote:
> On Sun, 2012-02-19 at 05:46 -0800, hpanvin@xxxxxxxxx wrote:
> > Vsyscall page, not vdso...
>
> Peter,
>
> My original patch was to check the %cs register against __KERNEL_CS, but
> IIRC, you said that userspace can change that register to anything it
> wanted before doing a long jump or something. Is this true for x86_64 as
> well? I guess it would be because x86_64 can support 32bit apps.
>
> Anyway, I'll add a check that makes sure that the RIP is less than the
> FIXADDR sections as well.

User space can change %cs, but it can never set it to __KERNEL_CS; 
specifically user space can never set the bottom two bits in CS to zero.

So this should be a better test.

(Now, doing the test that way plays havoc with the braindamage knows as 
Xen paravirt, but I don't think it's subject to this particular NMI code.)

	-hpa

--
To unsubscribe from this list: send the line "unsubscribe linux-kernel" in
the body of a message to majordomo@xxxxxxxxxxxxxxx
More majordomo info at  http://vger.kernel.org/majordomo-info.html
Please read the FAQ at  http://www.tux.org/lkml/