Re: [PATCH] x86/nmi/64: avoid passing user space rsp of pt_regs to nmi handler

[Josh Poimboeuf]

On Tue, Aug 22, 2017 at 05:09:19PM +0000, yang oliver wrote:
> From: Yong Yang <yangoliver@xxxxxxxxx>
> 
> 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