Messages in this thread | | | Date | Fri, 21 Aug 2015 14:06:16 -0700 | From | "H. Peter Anvin" <> | Subject | Re: [x86] copy_from{to}_user question |
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On 08/20/2015 09:35 PM, Borislav Petkov wrote: > On Thu, Aug 20, 2015 at 11:22:43AM -0700, H. Peter Anvin wrote: >> There is a valid reason to do this, which is that currently >> copy_{to,from}_user() effectively bypass SMAP as they don't verify that >> the kernel pointer is actually a kernel pointer. > > Well, we do STAC before we copy but SMAP is checking for supervisor > access to *user* data. But you say "kernel pointers" which is supervisor > data. What am I missing? >
What I'm saying is that we do do STAC, which *disables* SMAP. We have to do that because one pointer is known to be a user space pointer.
However, we currently don't verify that the *other* pointer is kernel space, which it is supposed to be (if not, we should be using copy_in_user). We have to do this manually since we have to STAC which means SMAP doesn't do anything at all. I believe it would be a good idea to add such checks (and they would even benefit non-SMAP hardware.)
-hpa
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