linux-kernel - Re: [PATCH 11/11] efi/x86: earlyprintk - Fix infinite loop on some screen widths

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Message-ID: <20181130080544.GC16084@gmail.com>
Date:   Fri, 30 Nov 2018 09:05:44 +0100
From:   Ingo Molnar <mingo@...nel.org>
To:     Ard Biesheuvel <ard.biesheuvel@...aro.org>
Cc:     linux-efi@...r.kernel.org, Thomas Gleixner <tglx@...utronix.de>,
        linux-kernel@...r.kernel.org, Andy Lutomirski <luto@...nel.org>,
        Arend van Spriel <arend.vanspriel@...adcom.com>,
        Bhupesh Sharma <bhsharma@...hat.com>,
        Borislav Petkov <bp@...en8.de>,
        Dave Hansen <dave.hansen@...el.com>,
        Eric Snowberg <eric.snowberg@...cle.com>,
        Hans de Goede <hdegoede@...hat.com>,
        Joe Perches <joe@...ches.com>,
        Jon Hunter <jonathanh@...dia.com>,
        Julien Thierry <julien.thierry@....com>,
        Marc Zyngier <marc.zyngier@....com>,
        Nathan Chancellor <natechancellor@...il.com>,
        Peter Zijlstra <peterz@...radead.org>,
        Sai Praneeth Prakhya <sai.praneeth.prakhya@...el.com>,
        Sedat Dilek <sedat.dilek@...il.com>,
        YiFei Zhu <zhuyifei1999@...il.com>
Subject: Re: [PATCH 11/11] efi/x86: earlyprintk - Fix infinite loop on some
 screen widths


* Ard Biesheuvel <ard.biesheuvel@...aro.org> wrote:

> From: YiFei Zhu <zhuyifei1999@...il.com>
> 
> An affected screen resolution is 1366 x 768, which width is not
> divisible by 8, the default font width. On such screens, when longer
> lines are earlyprintk'ed, overflow-to-next-line can never trigger,
> due to the left-most x-coordinate of the next character always less
> than the screen width. Earlyprintk will infinite loop in trying to
> print the rest of the string but unable to, due to the line being
> full.
> 
> This patch makes the trigger consider the right-most x-coordinate,
> instead of left-most, as the value to compare against the screen
> width threshold.
> 
> Signed-off-by: YiFei Zhu <zhuyifei1999@...il.com>
> Signed-off-by: Ard Biesheuvel <ard.biesheuvel@...aro.org>
> ---
>  arch/x86/platform/efi/early_printk.c | 2 +-
>  1 file changed, 1 insertion(+), 1 deletion(-)
> 
> diff --git a/arch/x86/platform/efi/early_printk.c b/arch/x86/platform/efi/early_printk.c
> index 7476b3b097e1..7138bc7a265c 100644
> --- a/arch/x86/platform/efi/early_printk.c
> +++ b/arch/x86/platform/efi/early_printk.c
> @@ -183,7 +183,7 @@ early_efi_write(struct console *con, const char *str, unsigned int num)
>  			num--;
>  		}
>  
> -		if (efi_x >= si->lfb_width) {
> +		if (efi_x + font->width > si->lfb_width) {
>  			efi_x = 0;
>  			efi_y += font->height;
>  		}

Any objections to marking this for -stable and queueing it up in 
efi/urgent as well?

Thanks,

	Ingo