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://email@example.com 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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