Re: [Xen-devel] [PATCH] x86: make IDT read-only

[Kees Cook <keescook@xxxxxxxxxxxx>]

On Mon, Apr 8, 2013 at 3:47 PM, H. Peter Anvin <hpa@xxxxxxxxx> wrote:
> On 04/08/2013 03:43 PM, Kees Cook wrote:
>> This makes the IDT unconditionally read-only. This primarily removes
>> the IDT from being a target for arbitrary memory write attacks. It has
>> an added benefit of also not leaking (via the "sidt" instruction) the
>> kernel base offset, if it has been relocated.
>>
>> Signed-off-by: Kees Cook <keescook@xxxxxxxxxxxx>
>> Cc: Eric Northup <digitaleric@xxxxxxxxxx>
>
> This isn't quite what this patch does, though, right?  There is still a
> writable IDT mapping at all times, which is different from a true
> readonly IDT, no?

Ah, I guess that's true. I suppose I should say it makes the memory
seen at the "sidt" location read-only. Can we make them both
read-only?

-Kees

--
Kees Cook
Chrome OS Security

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