Messages in this thread | | | From | Thomas Gleixner <> | Subject | Re: [RFC PATCH 1/4] x86/entry/nmi: Switch to the entry stack before switching to the thread stack | Date | Sun, 20 Jun 2021 13:23:08 +0200 |
| |
On Sat, Jun 19 2021 at 20:13, Andy Lutomirski wrote: > On Sat, Jun 19, 2021, at 3:51 PM, Thomas Gleixner wrote: >> On Tue, Jun 01 2021 at 14:52, Lai Jiangshan wrote: >> > From: Lai Jiangshan <laijs@linux.alibaba.com> >> > >> > Current kernel has no code to enforce data breakpoint not on the thread >> > stack. If there is any data breakpoint on the top area of the thread >> > stack, there might be problem. >> >> And because the kernel does not prevent data breakpoints on the thread >> stack we need to do more complicated things in the already horrible >> entry code instead of just doing the obvious and preventing data >> breakpoints on the thread stack? > > Preventing breakpoints on the thread stack is a bit messy: it’s > possible for a breakpoint to be set before the address in question is > allocated for the thread stack.
Bah.
> None of this is NMI-specific. #DB itself has the same problem.
Oh well.
> We could plausibly solve it differently by disarming breakpoints in > the entry asm before switching stacks. I’m not sure how much I like > that approach.
That's ugly and TBH in some sense is a breakpoint on the thread stack a violation of noinstr. I rather see them prevented completely, but yes that would have to be expanded to pretty much any variable which is touched in noinstr sections. What a mess.
Thanks,
tglx
| |