linux-kernel - Re: kernel oops loading i915 after "x86/asm: Pin sensitive CR4 bits" (873d50d58)

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Message-ID: <20190710084656.GB5447@altlinux.org>
Date:   Wed, 10 Jul 2019 11:46:56 +0300
From:   "Dmitry V. Levin" <ldv@...linux.org>
To:     Xi Ruoyao <xry111@...gyan1223.wang>
Cc:     Kees Cook <keescook@...omium.org>,
        Jani Nikula <jani.nikula@...ux.intel.com>,
        David Airlie <airlied@...ux.ie>, Jessica Yu <jeyu@...nel.org>,
        kernel-hardening@...ts.openwall.com,
        intel-gfx@...ts.freedesktop.org, dri-devel@...ts.freedesktop.org,
        linux-modules@...r.kernel.org, linux-kernel@...r.kernel.org
Subject: Re: kernel oops loading i915 after "x86/asm: Pin sensitive CR4 bits"
 (873d50d58)

Hi,

On Wed, Jul 10, 2019 at 01:44:17PM +0800, Xi Ruoyao wrote:
> Hello,
> 
> When I try to build and run the latest mainline kernel, it Oops loading i915
> module:
> 
> BUG: unable to handle page fault for address: ffffffff9edc1598
> #PF: supervisor write access in kernel mode
> #PF: error_code(0x0003) - permissions violation
> PGD 1a20c067 P4D 1a20c067 PUD 1a20d063 PMD 8000000019e000e1 
> Oops: 0003 [#1] SMP PTI
> 
> The complete log is attached.
> 
> Bisection tells "x86/asm: Pin sensitive CR4 bits" (873d50d58) is the first "bad"
> commit.  I can revert it and also "x86/asm: Pin sensitive CR0 bits" (8dbec27a2)
> to make the kernel "seems to" work.
> 
> I'm not a kernel expert so I can't tell if there is a bug in Kees' patch, or his
> patch exploits a bug in i915 or module loader.

This seems to be a kernel bug introduced after v5.2, see
https://lore.kernel.org/lkml/CAHk-=wjh+h_-fd-gJz=wor42ZNmqq46QnB90jyfzqmKLsLFWOg@mail.gmail.com/


-- 
ldv