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Message-ID: <20200805184800.GA12819@openwall.com>
Date: Wed, 5 Aug 2020 20:48:00 +0200
From: Solar Designer <solar@...nwall.com>
To: lkrg-users@...ts.openwall.com
Cc: Thomas Gleixner <tglx@...utronix.de>, Borislav Petkov <bp@...e.de>,
Kees Cook <keescook@...omium.org>
Subject: Re: lkrg: Fix build LKRG for kernel 5.8+
On Wed, Aug 05, 2020 at 07:46:48PM +0200, Mikhail Morfikov wrote:
> DKMS make.log for lkrg-0.8.1+git20200805 for kernel 5.8.0-amd64 (x86_64)
[...]
> ERROR: modpost: "native_write_cr4" [/var/lib/dkms/lkrg/0.8.1+git20200805/build/p_lkrg.ko] undefined!
Here's what this is about:
commit 21953ee5013d6632bee90ec89f2df59c69050db0
Author: Thomas Gleixner <tglx@...utronix.de>
Date: Sun Apr 26 18:55:15 2020 +0200
x86/cpu: Export native_write_cr4() only when CONFIG_LKTDM=m
Modules have no business poking into this but fixing this is for later.
[ bp: Carve out from an earlier patch. ]
Signed-off-by: Thomas Gleixner <tglx@...utronix.de>
Signed-off-by: Borislav Petkov <bp@...e.de>
Link: https://lkml.kernel.org/r/20200421092558.939985695@linutronix.de
where LKTDM is "Linux Kernel Dump Test Module".
We use native_write_cr4() via its wrapper __write_cr4() (in a kernel
header file) to restore SMEP and/or SMAP if these are unexpectedly
disabled yet kernel panic on this event is not enabled in LKRG
configuration (by default it is enabled).
We'll need to find a way around this. Perhaps will just access the
register directly from our own inline asm.
I am CC'ing this to a few people as a JFYI on what the change actually
achieved. With 5.8 already released, we'll have to work around this on
our end anyway.
On Wed, Aug 05, 2020 at 07:49:25PM +0200, Mikhail Morfikov wrote:
> At least it builds for 5.7.12 again. :)
I'd be surprised if it did not.
Thank you for testing!
Alexander
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