From: "Andy Lutomirski" <luto@kernel.org>
To: "Thomas Gleixner" <tglx@linutronix.de>,
"Lai Jiangshan" <jiangshanlai@gmail.com>,
"Linux Kernel Mailing List" <linux-kernel@vger.kernel.org>
Cc: "Steven Rostedt" <rostedt@goodmis.org>,
"Lai Jiangshan" <laijs@linux.alibaba.com>,
"Ingo Molnar" <mingo@redhat.com>,
"Borislav Petkov" <bp@alien8.de>,
"the arch/x86 maintainers" <x86@kernel.org>,
"H. Peter Anvin" <hpa@zytor.com>,
"Juergen Gross" <jgross@suse.com>,
"Peter Zijlstra (Intel)" <peterz@infradead.org>,
"Al Viro" <viro@zeniv.linux.org.uk>,
"Arvind Sankar" <nivedita@alum.mit.edu>
Subject: Re: [RFC PATCH 1/4] x86/entry/nmi: Switch to the entry stack before switching to the thread stack
Date: Sat, 19 Jun 2021 20:13:15 -0700 [thread overview]
Message-ID: <444d7139-e47a-4831-93d0-8eb5b9680fdc@www.fastmail.com> (raw)
In-Reply-To: <87bl81h3ih.ffs@nanos.tec.linutronix.de>
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.
None of this is NMI-specific. #DB itself has the same problem. 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.
>
> Confused.
>
> Thanks,
>
> tglx
>
next prev parent reply other threads:[~2021-06-20 3:13 UTC|newest]
Thread overview: 17+ messages / expand[flat|nested] mbox.gz Atom feed top
2021-06-01 6:52 [RFC PATCH 0/4] x86/entry/nmi: solidify userspace NMI entry Lai Jiangshan
2021-06-01 6:52 ` [RFC PATCH 1/4] x86/entry/nmi: Switch to the entry stack before switching to the thread stack Lai Jiangshan
2021-06-01 17:05 ` Steven Rostedt
2021-06-02 0:09 ` Lai Jiangshan
2021-06-02 0:16 ` Lai Jiangshan
2021-06-19 22:51 ` Thomas Gleixner
2021-06-20 3:13 ` Andy Lutomirski [this message]
2021-06-20 11:23 ` Thomas Gleixner
2021-06-25 10:40 ` Peter Zijlstra
2021-06-25 11:00 ` Peter Zijlstra
2021-06-26 7:03 ` Thomas Gleixner
2021-06-26 8:28 ` Peter Zijlstra
2021-06-01 6:52 ` [RFC PATCH 2/4] x86/entry/nmi: Use normal idtentry macro for NMI from userspace Lai Jiangshan
2021-06-03 17:36 ` Andy Lutomirski
2021-06-01 6:52 ` [RFC PATCH 3/4] x86/entry: Remove parameter rdx from macro PUSH_AND_CLEAR_REGS and PUSH_REGS Lai Jiangshan
2021-06-01 6:52 ` [RFC PATCH 4/4] x86/entry/nmi: unmask NMIs on userspace NMI when entry debugging Lai Jiangshan
2021-06-03 17:38 ` Andy Lutomirski
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