[PATCH v3 1/6] x86/uaccess: Avoid barrier_nospec() in 64-bit copy_from_user()

[Josh Poimboeuf]

On Tue, Oct 29, 2024 at 04:03:31PM -1000, Linus Torvalds wrote:
> Hmm. So it strikes me that this still does the "access_ok()", but
> that's pointless for the actual pointer masking case. One of the whole
> points of the pointer masking is that we can just do this without
> actually checking the address (or length) at all.
> 
> That's why the strncpy_from_user() has the pattern of
> 
>         if (can_do_masked_user_access()) {
>                 ... don't worry about the size of the address space ..
> 
> and I think this code should do that too.
> 
> IOW, I think we can do even better than your patch with something
> (UNTESTED!) like the attached.
> 
> That will also mean that any other architecture that starts doing the
> user address masking trick will pick up on this automatically.
> 
> Hmm?

Yeah, it makes sense to hook into that existing
can_do_masked_user_access() thing.  The patch looks good, and it boots
without blowing up.  Thanks!

Reviewed-by: Josh Poimboeuf <jpoimboe at kernel.org>

-- 
Josh