[<prev] [next>] [<thread-prev] [thread-next>] [day] [month] [year] [list]
Date: Tue, 6 Aug 2019 17:35:30 +0200
From: Borislav Petkov <bp@...en8.de>
To: Steven Rostedt <rostedt@...dmis.org>
Cc: Thomas Garnier <thgarnie@...omium.org>,
kernel-hardening@...ts.openwall.com, kristen@...ux.intel.com,
keescook@...omium.org, Andy Lutomirski <luto@...nel.org>,
Thomas Gleixner <tglx@...utronix.de>,
Ingo Molnar <mingo@...hat.com>, "H. Peter Anvin" <hpa@...or.com>,
x86@...nel.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCH v9 04/11] x86/entry/64: Adapt assembly for PIE support
On Tue, Aug 06, 2019 at 09:59:42AM -0400, Steven Rostedt wrote:
> As Peter stated later in this thread, we only have the IRQ stack frame saved
> here, because we just took an NMI, and this is the logic to determine if it
> was a nested NMI or not (where we have to be *very* careful about touching the
> stack!)
>
> That said, the code modified here is to test the NMI nesting logic (only
> enabled with CONFIG_DEBUG_ENTRY), and what it is doing is re-enabling NMIs
> before calling the first NMI handler, to help trigger nested NMIs without the
> need of a break point or page fault (iret enables NMIs again).
>
> This code is in the path of the "first nmi" (we confirmed that this is not
> nested), which means that it should be safe to push onto the stack.
Thanks for the explanation!
> Yes, we need to save and restore whatever reg we used. The only comment I
> would make is to use %rdx instead of %rax as that has been our "scratch"
> register used before saving pt_regs. Just to be consistent.
Yap, makes sense.
Thx.
--
Regards/Gruss,
Boris.
Good mailing practices for 400: avoid top-posting and trim the reply.
Powered by blists - more mailing lists
Confused about mailing lists and their use?
Read about mailing lists on Wikipedia
and check out these
guidelines on proper formatting of your messages.
