Messages in this thread | | | From | Linus Torvalds <> | Date | Thu, 28 Mar 2019 08:48:33 -0700 | Subject | Re: [PATCH] x86/asm: add __user on copy_user_handle_tail() pointers |
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On Thu, Mar 28, 2019 at 12:24 AM Borislav Petkov <bp@alien8.de> wrote: > > Well, but copy_user_generic() (which ends up calling the > copy_user_handle_tail() eventually) casts those __user pointers to > (__force void *). Converting them back to __user looks strange to me. > > Linus?
Well, it does that because the x86 version of copy_user_generic() can work in either direction, so it works when either the source or destination (or both) are user pointers, but they don't _have_ to be.
So the "userness" of a pointer in that context is a bit ambiguous, and so we've picked the pointers to be just plain "void *".
That said, arguably we should have gone the other way and just made them both "__user" pointers, and do the cast the other way around.
But there's no absolutely right answer here, and nobody should ever use copy_user_generic() directly (ie it is very much meant to be only used as a internal helper for the cases that get the pointer annotations right).
I do think Ben's patch is probably the right thing to do.
And we could do the same thing to copy_user_generic(), but that would require switching the casts around in the callers, so may not be worth the noise.
Linus
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