linux-kernel - Re: [RFC] x86_64: A real proposal for iret-less return to kernel

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Message-ID: <CALCETrWR+PqM6SxzqoRwghPgihjQCJ74VCN5AsAq3Kja64uCTg@mail.gmail.com>
Date:	Wed, 21 May 2014 14:59:38 -0700
From:	Andy Lutomirski <luto@...capital.net>
To:	Borislav Petkov <bp@...en8.de>
Cc:	Jiri Kosina <jkosina@...e.cz>,
	Thomas Gleixner <tglx@...utronix.de>,
	Linus Torvalds <torvalds@...ux-foundation.org>,
	Steven Rostedt <rostedt@...dmis.org>,
	Andi Kleen <andi@...stfloor.org>,
	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
	"H. Peter Anvin" <hpa@...or.com>, Ingo Molnar <mingo@...nel.org>,
	Tony Luck <tony.luck@...el.com>
Subject: Re: [RFC] x86_64: A real proposal for iret-less return to kernel

On Wed, May 21, 2014 at 2:55 PM, Borislav Petkov <bp@...en8.de> wrote:
> On Wed, May 21, 2014 at 02:52:55PM -0700, Andy Lutomirski wrote:
>> Why is it a problem if user_mode_vm(regs)?  Conversely, why is sending
>> a signal a remotely reasonable thing to do if !user_mode_vm(regs)?
>
> Let me quote Jiri:
>
> (1) task sends signal to itself
> (2) it acquires sighand->siglock so that it's able to queue the signal
> (3) MCE triggers

...and !user_mode_vm(regs), and hence we're IN_KERNEL, and we should
presumably just panic instead of trying to send a signal.

I missed the IN_KERNEL thing because I didn't realize that ->cs was
copied to struct mce.

--Andy
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