Subject: Re: mmotm 2020-05-13-20-30 uploaded (objtool warnings)

From: Peter Zijlstra <[email-masked]>
Date: Fri, 29 May 2020 16:35:56 +0200

On Fri, May 29, 2020 at 03:57:51PM +0200, Christoph Hellwig wrote:
> On Thu, May 28, 2020 at 07:20:05PM +0200, Peter Zijlstra wrote:
> > > on x86_64:
> > > 
> > > arch/x86/lib/csum-wrappers_64.o: warning: objtool: csum_and_copy_from_user()+0x2a4: call to memset() with UACCESS enabled
> > > arch/x86/lib/csum-wrappers_64.o: warning: objtool: csum_and_copy_to_user()+0x243: return with UACCESS enabled
> > 
> > Urgh, that's horrible code. That's got plain stac()/clac() calls on
> > instead of the regular uaccess APIs.
> 
> Does it?  If this is from the code in linux-next, then the code does a
> user_access_begin/end in csum_and_copy_{from,to}_user, then uses
> unsafe_{get,put}_user inside those function itself.  But then they call
> csum_partial_copy_generic with the __user casted away, but without any
> comment on why this is safe.

Bah, clearly I was looking at the wrong tree. You're right, Al cleaned
it all up.

Let me try and figure out why objtool is unhappy with it.