linux-kernel - Re: [PATCH v9 09/12] x86, mpx: decode MPX instruction to get bound violation information

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Date:	Fri, 31 Oct 2014 10:09:13 +0100 (CET)
From:	Thomas Gleixner <tglx@...utronix.de>
To:	Ren Qiaowei <qiaowei.ren@...el.com>
cc:	Dave Hansen <dave.hansen@...el.com>,
	"H. Peter Anvin" <hpa@...or.com>, Ingo Molnar <mingo@...hat.com>,
	x86@...nel.org, linux-mm@...ck.org, linux-kernel@...r.kernel.org,
	linux-ia64@...r.kernel.org, linux-mips@...ux-mips.org
Subject: Re: [PATCH v9 09/12] x86, mpx: decode MPX instruction to get bound
 violation information

On Fri, 31 Oct 2014, Ren Qiaowei wrote:
> On 10/31/2014 06:38 AM, Dave Hansen wrote:
> > > @@ -316,6 +317,11 @@ dotraplinkage void do_bounds(struct pt_regs *regs,
> > > long error_code)
> > >   		break;
> > > 
> > >   	case 1: /* Bound violation. */
> > > +		do_mpx_bounds(regs, &info, xsave_buf);
> > > +		do_trap(X86_TRAP_BR, SIGSEGV, "bounds", regs,
> > > +				error_code, &info);
> > > +		break;
> > > +
> > >   	case 0: /* No exception caused by Intel MPX operations. */
> > >   		do_trap(X86_TRAP_BR, SIGSEGV, "bounds", regs, error_code,
> > > NULL);
> > >   		break;
> > > 
> > 
> > So, siginfo is stack-allocarted here.  do_mpx_bounds() can error out if
> > it sees an invalid bndregno.  We still send the signal with the &info
> > whether or not we filled the 'info' in do_mpx_bounds().
> > 
> > Can't this leak some kernel stack out in the 'info'?
> > 
> 
> This should check the return value of do_mpx_bounds and should be fixed.

And how's that answering Dave's question about leaking stack information? 

Thanks,

	tglx
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