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

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Date:   Wed, 11 Mar 2020 09:30:15 +0800
From:   Walter Wu <walter-zh.wu@...iatek.com>
To:     Peter Zijlstra <peterz@...radead.org>
CC:     Randy Dunlap <rdunlap@...radead.org>, <akpm@...ux-foundation.org>,
        <broonie@...nel.org>, <linux-fsdevel@...r.kernel.org>,
        <linux-kernel@...r.kernel.org>, <linux-mm@...ck.org>,
        <linux-next@...r.kernel.org>, <mhocko@...e.cz>,
        <mm-commits@...r.kernel.org>, <sfr@...b.auug.org.au>,
        Josh Poimboeuf <jpoimboe@...hat.com>, <dvyukov@...gle.com>
Subject: Re: mmotm 2020-03-03-22-28 uploaded (warning: objtool:)

On Thu, 2020-03-05 at 10:54 +0100, Peter Zijlstra wrote:
> On Thu, Mar 05, 2020 at 05:16:22PM +0800, Walter Wu wrote:
> > 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.
> 
> The patch is trivial; and all you need is an x86_64 (cross) compiler to
> reproduce.
> 
> 
> diff --git a/mm/kasan/common.c b/mm/kasan/common.c
> index ad2dc0c9cc17..2906358e42f0 100644
> --- a/mm/kasan/common.c
> +++ b/mm/kasan/common.c
> @@ -618,16 +618,17 @@ extern bool report_enabled(void);
>  
>  bool kasan_report(unsigned long addr, size_t size, bool is_write, unsigned long ip)
>  {
> -	unsigned long flags;
> +	unsigned long flags = user_access_save();
> +	bool ret = false;
>  
> -	if (likely(!report_enabled()))
> -		return false;
> +	if (likely(report_enabled())) {
> +		__kasan_report(addr, size, is_write, ip);
> +		ret = true;
> +	}
>  
> -	flags = user_access_save();
> -	__kasan_report(addr, size, is_write, ip);
>  	user_access_restore(flags);
>  
> -	return true;
> +	return ret;
>  }
>  
>  #ifdef CONFIG_MEMORY_HOTPLUG

Reviewed-and-tested-by: