linux-kernel - Re: [PATCH v3 2/3] x86/entry: Clear registers for 64bit exceptions/interrupts

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Message-ID: <20180206104834.h34mme4m5p6c5jcr@gmail.com>
Date:   Tue, 6 Feb 2018 11:48:34 +0100
From:   Ingo Molnar <mingo@...nel.org>
To:     Dominik Brodowski <linux@...inikbrodowski.net>
Cc:     Dan Williams <dan.j.williams@...el.com>, tglx@...utronix.de,
        Andi Kleen <ak@...ux.intel.com>, torvalds@...ux-foundation.org,
        linux-kernel@...r.kernel.org, luto@...nel.org
Subject: Re: [PATCH v3 2/3] x86/entry: Clear registers for 64bit
 exceptions/interrupts


* Dominik Brodowski <linux@...inikbrodowski.net> wrote:

> On Mon, Feb 05, 2018 at 05:18:11PM -0800, Dan Williams wrote:
> > @@ -1178,6 +1180,7 @@ ENTRY(paranoid_entry)
> >  	cld
> >  	SAVE_C_REGS 8
> >  	SAVE_EXTRA_REGS 8
> > +	CLEAR_REGS_NOSPEC
> >  	ENCODE_FRAME_POINTER 8
> >  	movl	$1, %ebx
> >  	movl	$MSR_GS_BASE, %ecx
> > @@ -1185,7 +1188,6 @@ ENTRY(paranoid_entry)
> >  	testl	%edx, %edx
> >  	js	1f				/* negative -> in kernel */
> >  	SWAPGS
> > -	xorl	%ebx, %ebx
> 
> Here, %ebx will be filled with $1 (see code snipped above) *after* the
> call to CLEAR_REGS_NOSPEC. That's what this line has been clearing in the
> past. So I'm not sure whether this line should be removed.

Good point - I have fixed this bug in the tip:x86/pti version of the patch.

Thanks,

	Ingo