Messages in this thread | | | Subject | Re: [PATCH 10/17] prmem: documentation | From | Igor Stoppa <> | Date | Tue, 13 Nov 2018 21:01:43 +0200 |
| |
On 13/11/2018 20:35, Andy Lutomirski wrote: > On Tue, Nov 13, 2018 at 10:26 AM Igor Stoppa <igor.stoppa@huawei.com> wrote:
[...]
>> The high level API could be something like: >> >> wr_memcpy(void *src, void *dst, uint_t size)
[...]
> If you call a wr_memcpy() function with the signature you suggested, > then you can overwrite any memory of this type. Having a different > mm_struct under the hood makes no difference. As far as I'm > concerned, for *dynamically allocated* rare-writable memory, you might > as well allocate all the paging structures at the same time, so the > mm_struct will always contain the mappings. If there are serious bugs > in wr_memcpy() that cause it to write to the wrong place, we have > bigger problems.
Beside bugs, I'm also thinking about possible vulnerability. It might be overthinking, though.
I do not think it's possible to really protect against control flow attacks, unless there is some support from the HW and/or the compiler.
What is left, are data-based attacks. In this case, it would be an attacker using one existing wr_ invocation with doctored parameters.
However, there is always the objection that it would be possible to come up with a "writing kit" for plowing through the page tables and unprotect anything that might be of value.
Ideally, that should be the only type of data-based attack left.
In practice, it might just be an excess of paranoia from my side.
> I can imagine that we'd want a *typed* wr_memcpy()-like API some day, > but that can wait for v2. And it still doesn't obviously need > multiple mm_structs.
I left that out, for now, but yes, typing would play some role here.
[...]
> I think it's entirely reasonable for the API to internally break up > very large memcpys.
The criteria for deciding if/how to break it down is not clear to me, though. The single page was easy, but might be (probably is) too much.
-- igor
| |