Patchwork [11/11] efi/x86: earlyprintk - Fix infinite loop on some screen widths

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Submitter Ard Biesheuvel
Date Nov. 29, 2018, 5:12 p.m.
Message ID <20181129171230.18699-12-ard.biesheuvel@linaro.org>
Download mbox | patch
Permalink /patch/668357/
State New
Headers show

Comments

Ard Biesheuvel - Nov. 29, 2018, 5:12 p.m.
From: YiFei Zhu <zhuyifei1999@gmail.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@gmail.com>
Signed-off-by: Ard Biesheuvel <ard.biesheuvel@linaro.org>
---
 arch/x86/platform/efi/early_printk.c | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)
Ingo Molnar - Nov. 30, 2018, 8:05 a.m.
* Ard Biesheuvel <ard.biesheuvel@linaro.org> wrote:

> From: YiFei Zhu <zhuyifei1999@gmail.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@gmail.com>
> Signed-off-by: Ard Biesheuvel <ard.biesheuvel@linaro.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
Ard Biesheuvel - Nov. 30, 2018, 8:32 a.m.
On Fri, 30 Nov 2018 at 09:05, Ingo Molnar <mingo@kernel.org> wrote:
>
>
> * Ard Biesheuvel <ard.biesheuvel@linaro.org> wrote:
>
> > From: YiFei Zhu <zhuyifei1999@gmail.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@gmail.com>
> > Signed-off-by: Ard Biesheuvel <ard.biesheuvel@linaro.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?
>

No that is fine.

Patch

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;
 		}