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

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Message-Id: <20181129171230.18699-12-ard.biesheuvel@linaro.org>
Date:   Thu, 29 Nov 2018 18:12:30 +0100
From:   Ard Biesheuvel <ard.biesheuvel@...aro.org>
To:     linux-efi@...r.kernel.org, Ingo Molnar <mingo@...nel.org>,
        Thomas Gleixner <tglx@...utronix.de>
Cc:     Ard Biesheuvel <ard.biesheuvel@...aro.org>,
        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: [PATCH 11/11] efi/x86: earlyprintk - Fix infinite loop on some screen widths

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;
 		}
-- 
2.19.1