Re: [x86] copy_from{to}_user question

[yalin wang]

> On Aug 22, 2015, at 17:05, Borislav Petkov <bp@xxxxxxx> wrote:
> 
> On Fri, Aug 21, 2015 at 02:06:16PM -0700, H. Peter Anvin wrote:
>> 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.)
> 
> Ah, ok, so we're on the same page.
> 
> And yep, Linus gave the probe_kernel_read() suggestion in another mail.
> 
i am not clear about what is STAC / SMAP ?
could you give me a link for understanding ?

Linus suggest to use probe_kernel_read() , but also said it is 
not efficient to use it, because we need copy the data 2 times by this method.

my patch suggests to use copy_in_user() ,
but seems not a generic(portable) function on all architectures.

Thanks--
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