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Date:   Wed, 21 Apr 2021 12:49:14 -0700
From:   Kees Cook <keescook@chromium.org>
To:     Greg Kroah-Hartman <gregkh@linuxfoundation.org>
Cc:     linux-kernel@vger.kernel.org, Aditya Pakki <pakki001@umn.edu>,
        Thomas Gleixner <tglx@linutronix.de>, kjlu@umn.edu,
        Borislav Petkov <bp@alien8.de>,
        "H. Peter Anvin" <hpa@zytor.com>, Joe Perches <joe@perches.com>,
        Nicolai Stange <nstange@suse.de>,
        Roland Dreier <roland@purestorage.com>
Subject: Re: [PATCH 113/190] Revert "x86/hpet: Prevent potential NULL pointer
 dereference"
Message-ID: <202104211245.F5FEC8D15D@keescook>
References: <20210421130105.1226686-1-gregkh@linuxfoundation.org>
 <20210421130105.1226686-114-gregkh@linuxfoundation.org>
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On Wed, Apr 21, 2021 at 02:59:48PM +0200, Greg Kroah-Hartman wrote:
> This reverts commit 2e84f116afca3719c9d0a1a78b47b48f75fd5724.
> 
> Commits from @umn.edu addresses have been found to be submitted in "bad
> faith" to try to test the kernel community's ability to review "known
> malicious" changes.  The result of these submissions can be found in a
> paper published at the 42nd IEEE Symposium on Security and Privacy
> entitled, "Open Source Insecurity: Stealthily Introducing
> Vulnerabilities via Hypocrite Commits" written by Qiushi Wu (University
> of Minnesota) and Kangjie Lu (University of Minnesota).
> 
> Because of this, all submissions from this group must be reverted from
> the kernel tree and will need to be re-reviewed again to determine if
> they actually are a valid fix.  Until that work is complete, remove this
> change to ensure that no problems are being introduced into the
> codebase.
> 
> Cc: Aditya Pakki <pakki001@umn.edu>
> Cc: Thomas Gleixner <tglx@linutronix.de>
> Cc: kjlu@umn.edu
> Cc: Borislav Petkov <bp@alien8.de>
> Cc: "H. Peter Anvin" <hpa@zytor.com>
> Cc: Kees Cook <keescook@chromium.org>
> Cc: Joe Perches <joe@perches.com>
> Cc: Nicolai Stange <nstange@suse.de>
> Cc: Roland Dreier <roland@purestorage.com>
> Cc: https
> Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
> ---
>  arch/x86/kernel/hpet.c | 2 --
>  1 file changed, 2 deletions(-)
> 
> diff --git a/arch/x86/kernel/hpet.c b/arch/x86/kernel/hpet.c
> index 08651a4e6aa0..0515a97bf6f5 100644
> --- a/arch/x86/kernel/hpet.c
> +++ b/arch/x86/kernel/hpet.c
> @@ -930,8 +930,6 @@ int __init hpet_enable(void)
>  		return 0;
>  
>  	hpet_set_mapping();
> -	if (!hpet_virt_address)
> -		return 0;
>  
>  	/* Validate that the config register is working */
>  	if (!hpet_cfg_working())

FWIW, this patch looks harmless. It is checking for a failure in
hpet_set_mapping(), and avoids the following code from performing
0-offset reads. hpet_set_mapping() is likely to never fail in real-world
situations. *shrug*

I think it would make more sense for the check to live in
hpet_cfg_working(), though.

-- 
Kees Cook