linux-kernel - Re: [tip: x86/urgent] x86/kexec: Use up-to-dated screen

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: <877drb1lhx.fsf@nanos.tec.linutronix.de>
Date:   Tue, 27 Oct 2020 21:07:06 +0100
From:   Thomas Gleixner <tglx@...utronix.de>
To:     tip-bot2 for Kairui Song <tip-bot2@...utronix.de>,
        linux-tip-commits@...r.kernel.org
Cc:     Kairui Song <kasong@...hat.com>, Ingo Molnar <mingo@...nel.org>,
        x86 <x86@...nel.org>, LKML <linux-kernel@...r.kernel.org>
Subject: Re: [tip: x86/urgent] x86/kexec: Use up-to-dated screen_info copy to fill boot params

On Wed, Oct 14 2020 at 15:43, tip-bot wrote:
> The following commit has been merged into the x86/urgent branch of tip:
> x86/kexec: Use up-to-dated screen_info copy to fill boot params
>
> kexec_file_load() currently reuses the old boot_params.screen_info,
> but if drivers have change the hardware state, boot_param.screen_info
> could contain invalid info.
>
> For example, the video type might be no longer VGA, or the frame buffer
> address might be changed. If the kexec kernel keeps using the old screen_info,
> kexec'ed kernel may attempt to write to an invalid framebuffer
> memory region.
>
> There are two screen_info instances globally available, boot_params.screen_info
> and screen_info. Later one is a copy, and is updated by drivers.
>  
>  	/* Copying screen_info will do? */
> -	memcpy(&params->screen_info, &boot_params.screen_info,
> -				sizeof(struct screen_info));
> +	memcpy(&params->screen_info, &screen_info, sizeof(struct screen_info));

Well, that's better than what we had before, but how is this correct
vs. the following sequence:

    kexec_load()
    change_screen()
    kexec()

Hmm?

Thanks,

        tglx