Re: mmotm 2020-03-03-22-28 uploaded (warning: objtool:)

Walter Wu
2020-03-05T09:16:32Z

On Thu, 2020-03-05 at 09:18 +0100, Peter Zijlstra wrote:
> On Thu, Mar 05, 2020 at 09:17:17AM +0100, Peter Zijlstra wrote:
> > On Wed, Mar 04, 2020 at 09:34:49AM -0800, Randy Dunlap wrote:
>
> > > mm/kasan/common.o: warning: objtool: kasan_report()+0x13: call to report_enabled() with UACCESS enabled
> >
> > I used next/master instead, and found the below broken commit
> > responsible for this.
>
> > @@ -634,12 +637,20 @@ void kasan_free_shadow(const struct vm_struct *vm)
> > #endif
> >
> > extern void __kasan_report(unsigned long addr, size_t size, bool is_write, unsigned long ip);
> > +extern bool report_enabled(void);
> >
> > -void kasan_report(unsigned long addr, size_t size, bool is_write, unsigned long ip)
> > +bool kasan_report(unsigned long addr, size_t size, bool is_write, unsigned long ip)
> > {
> > - unsigned long flags = user_access_save();
> > + unsigned long flags;
> > +
> > + if (likely(!report_enabled()))
> > + return false;
>
> This adds an explicit call before the user_access_save() and that is a
> straight on bug.
>
Hi Peter,

Thanks for your help. Unfortunately, I don't reproduce it in our
environment, so I have asked Stephen, if I can reproduce it, then we
will send new patch.

Thanks.

Walter

> > +
> > + flags = user_access_save();
> > __kasan_report(addr, size, is_write, ip);
> > user_access_restore(flags);
> > +
> > + return true;
> > }