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.
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