linux-kernel - Re: [PATCH] x86/nmi/64: avoid passing user space rsp of pt

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Message-ID: <20170822175115.k3tdjlkltua7lkiu@treble>
Date:   Tue, 22 Aug 2017 12:51:16 -0500
From:   Josh Poimboeuf <jpoimboe@...hat.com>
To:     yang oliver <yang_oliver@...mail.com>
Cc:     "tglx@...utronix.de" <tglx@...utronix.de>,
        "mingo@...hat.com" <mingo@...hat.com>,
        "hpa@...or.com" <hpa@...or.com>,
        "luto@...nel.org" <luto@...nel.org>,
        "x86@...nel.org" <x86@...nel.org>,
        "rostedt@...dmis.org" <rostedt@...dmis.org>,
        "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
        Yong Yang <yangoliver@...il.com>
Subject: Re: [PATCH] x86/nmi/64: avoid passing user space rsp of pt_regs to
 nmi handler

On Tue, Aug 22, 2017 at 05:09:19PM +0000, yang oliver wrote:
> From: Yong Yang <yangoliver@...il.com>
> 
> While NMI interrupts the very beginning of SYSCALL, the rsp could
> be still user space address without loading kernel address. Then
> the pt_regs constructed by the NMI entry point could have a user
> space rsp. If a NMI handler tried to dump stack by using this rsp,
> it can cause the kernel panic.

To me this sounds like an unwinder bug.  The unwinder is supposed to
have checks to prevent it from accessing user space.  I know you had
previously reported this for an older (pre-4.9) kernel.  Have you
verified the bug still exists on a recent kernel?

-- 
Josh