linux-kernel - Re: [PATCH v9 04/11] x86/entry/64: Adapt assembly for PIE support

lists.openwall.net		lists / announce owl-users owl-dev john-users john-dev passwdqc-users yescrypt popa3d-users / oss-security kernel-hardening musl sabotage tlsify passwords / crypt-dev xvendor / Bugtraq Full-Disclosure linux-kernel linux-netdev linux-ext4 linux-hardening linux-cve-announce PHC
Open Source and information security mailing list archives

Hash Suite: Windows password security audit tool. GUI, reports in PDF.

[<prev] [next>] [<thread-prev] [thread-next>] [day] [month] [year] [list]

Message-ID: <20190806153530.GC25897@zn.tnic>
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.