linux-kernel - Re: [PATCH 12/31] x86/entry/32: Add PTI cr3 switch to non-NMI entry/exit points

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Message-ID: <20180301120326.GN16484@8bytes.org>
Date:   Thu, 1 Mar 2018 13:03:26 +0100
From:   Joerg Roedel <joro@...tes.org>
To:     Waiman Long <longman@...hat.com>
Cc:     Thomas Gleixner <tglx@...utronix.de>,
        Ingo Molnar <mingo@...nel.org>,
        "H . Peter Anvin" <hpa@...or.com>, x86@...nel.org,
        linux-kernel@...r.kernel.org, linux-mm@...ck.org,
        Linus Torvalds <torvalds@...ux-foundation.org>,
        Andy Lutomirski <luto@...nel.org>,
        Dave Hansen <dave.hansen@...el.com>,
        Josh Poimboeuf <jpoimboe@...hat.com>,
        Juergen Gross <jgross@...e.com>,
        Peter Zijlstra <peterz@...radead.org>,
        Borislav Petkov <bp@...en8.de>, Jiri Kosina <jkosina@...e.cz>,
        Boris Ostrovsky <boris.ostrovsky@...cle.com>,
        Brian Gerst <brgerst@...il.com>,
        David Laight <David.Laight@...lab.com>,
        Denys Vlasenko <dvlasenk@...hat.com>,
        Eduardo Valentin <eduval@...zon.com>,
        Greg KH <gregkh@...uxfoundation.org>,
        Will Deacon <will.deacon@....com>, aliguori@...zon.com,
        daniel.gruss@...k.tugraz.at, hughd@...gle.com, keescook@...gle.com,
        Andrea Arcangeli <aarcange@...hat.com>,
        Waiman Long <llong@...hat.com>, Pavel Machek <pavel@....cz>,
        jroedel@...e.de
Subject: Re: [PATCH 12/31] x86/entry/32: Add PTI cr3 switch to non-NMI
 entry/exit points

On Tue, Feb 27, 2018 at 02:18:36PM -0500, Waiman Long wrote:
> On 02/09/2018 04:25 AM, Joerg Roedel wrote:
> >  	SAVE_ALL
> >  	ENCODE_FRAME_POINTER
> > +
> > +	/* Make sure we are running on kernel cr3 */
> > +	SWITCH_TO_KERNEL_CR3 scratch_reg=%eax
> > +
> >  	xorl	%edx, %edx			# error code 0
> >  	movl	%esp, %eax			# pt_regs pointer
> >  
> 
> The debug exception calls ret_from_exception on exit. If coming from
> userspace, the C function prepare_exit_to_usermode() will be called.
> With the PTI-32 code, it means that function will be called with the
> entry stack instead of the task stack. This can be problematic as macro
> like current won't work anymore.

This is not different from before, no? The debug handler already can be
entered on entry stack before this patch-set.


	Joerg