linux-kernel - Re: [PATCH] uprobes/core: handle breakpoint and signal step exception.

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Date:	Fri, 9 Mar 2012 08:33:48 +0100
From:	Ingo Molnar <mingo@...e.hu>
To:	Srikar Dronamraju <srikar@...ux.vnet.ibm.com>
Cc:	"H. Peter Anvin" <hpa@...or.com>,
	Peter Zijlstra <peterz@...radead.org>,
	Linus Torvalds <torvalds@...ux-foundation.org>,
	Oleg Nesterov <oleg@...hat.com>,
	LKML <linux-kernel@...r.kernel.org>,
	Christoph Hellwig <hch@...radead.org>,
	Steven Rostedt <rostedt@...dmis.org>,
	Thomas Gleixner <tglx@...utronix.de>,
	Masami Hiramatsu <masami.hiramatsu.pt@...achi.com>,
	Anton Arapov <anton@...hat.com>,
	Ananth N Mavinakayanahalli <ananth@...ibm.com>,
	Jim Keniston <jkenisto@...ux.vnet.ibm.com>,
	Jiri Olsa <jolsa@...hat.com>, Josh Stone <jistone@...hat.com>
Subject: Re: [PATCH] uprobes/core: handle breakpoint and signal step
 exception.


* Srikar Dronamraju <srikar@...ux.vnet.ibm.com> wrote:

> * Ingo Molnar <mingo@...e.hu> [2012-03-08 14:48:09]:
> 
> > 
> > * Srikar Dronamraju <srikar@...ux.vnet.ibm.com> wrote:
> > 
> > > @@ -233,9 +233,11 @@ static inline void __user *arch_compat_alloc_user_space(long len)
> > >  
> > >  	if (test_thread_flag(TIF_IA32)) {
> > >  		sp = task_pt_regs(current)->sp;
> > > +#ifdef CONFIG_X86_64
> > >  	} else {
> > >  		/* -128 for the x32 ABI redzone */
> > >  		sp = __this_cpu_read(old_rsp) - 128;
> > > +#endif
> > >  	}
> > >  
> > >  	return (void __user *)round_down(sp - len, 16);
> > 
> > So 'sp' is undefined if that TIF check fails?
> > 
> > Also, on a 32-bit kernel the TIF check probably fails all the 
> > time, because we don't set TIF_IA32 (and don't know that flag).
> 
> > 
> > It would probably be better to make the whole helper inline 
> > #ifdef 64-bit, it does not look very useful on 32-bit.
> > 
> 
> arch_compat_alloc_user_space gets called from compat_alloc_user_space
> which is arch agnostic and exported too.
> 
> So I will change this to
> 
> void __user *arch_compat_alloc_user_space(long len)
> {
>   	if (is_ia32_compat_task(current))
>   		sp = task_pt_regs(current)->sp;
> #ifdef CONFIG_X86_64
>   	else
>   		/* -128 for the x32 ABI redzone */
>   		sp = __this_cpu_read(old_rsp) - 128;
> #endif
>   
>   	return (void __user *)round_down(sp - len, 16);
> }
> 
> where is_ia32_compat_task() is the new macro that you 
> suggested we put in compat.h which would return true if the 
> task is 32 bit emulated on x86_64 or running on i386 machine.
> 
> Hence we can avoid the case where sp is not set.

Ok - looks good at first glance.

Thanks,

	Ingo
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