[PATCH RESEND] arm64: don't dump stack for usermode address in show_regs

[will.deacon@arm.com (Will Deacon)]

On Wed, Aug 29, 2018 at 10:58:00PM +0800, Ding Tianhong wrote:
> On 2018/8/29 19:54, Will Deacon wrote:
> > This looks like we're somehow dereferencing the user frame-pointer from the
> > READ_ONCE_NOCHECK in unwind_frame(). However, I really don't see how that
> > can happen, since the kernel entry code pushes a dummy frame record or
> > zeroes, which will terminate any backtrace before we hit the user
> > addresses. Furthermore, we explicitly check that the frame pointer points
> > to an accessible stack before we dereference it. Hmm.
> > 
> 
> I found the patch 12964443e8d1 ("arm64: add on_accessible_stack()")
> already fix this in kernel v4.14, my kernel version is older than this and
> miss this patch for a long time, so I think this is the reason that I met
> this problem, thanks for remind me.

Ok, but in future please state up-front if you're reporting an issue that
you're seeing on something older than mainline. I spent an hour reading
through this code today looking for a bug we'd already fixed :(

Will