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To:     linux-kernel@vger.kernel.org
Cc:     Greg Kroah-Hartman <gregkh@linuxfoundation.org>,
        stable@vger.kernel.org, YiFei Zhu <zhuyifei1999@gmail.com>,
        Ard Biesheuvel <ard.biesheuvel@linaro.org>,
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        Arend van Spriel <arend.vanspriel@broadcom.com>,
        Bhupesh Sharma <bhsharma@redhat.com>,
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        Hans de Goede <hdegoede@redhat.com>,
        Joe Perches <joe@perches.com>,
        Jon Hunter <jonathanh@nvidia.com>,
        Julien Thierry <julien.thierry@arm.com>,
        Linus Torvalds <torvalds@linux-foundation.org>,
        Marc Zyngier <marc.zyngier@arm.com>,
        Matt Fleming <matt@codeblueprint.co.uk>,
        Nathan Chancellor <natechancellor@gmail.com>,
        Peter Zijlstra <peterz@infradead.org>,
        Sai Praneeth Prakhya <sai.praneeth.prakhya@intel.com>,
        Sedat Dilek <sedat.dilek@gmail.com>,
        Thomas Gleixner <tglx@linutronix.de>,
        linux-efi@vger.kernel.org, Ingo Molnar <mingo@kernel.org>,
        Sasha Levin <sashal@kernel.org>
Subject: [PATCH 4.9 34/61] x86/earlyprintk/efi: Fix infinite loop on some screen widths
Date:   Thu, 20 Dec 2018 10:18:34 +0100
Message-Id: <20181220085845.113058962@linuxfoundation.org>
In-Reply-To: <20181220085843.743900603@linuxfoundation.org>
References: <20181220085843.743900603@linuxfoundation.org>
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4.9-stable review patch.  If anyone has any objections, please let me know.

------------------

[ Upstream commit 79c2206d369b87b19ac29cb47601059b6bf5c291 ]

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>
Cc: Andy Lutomirski <luto@kernel.org>
Cc: Arend van Spriel <arend.vanspriel@broadcom.com>
Cc: Bhupesh Sharma <bhsharma@redhat.com>
Cc: Borislav Petkov <bp@alien8.de>
Cc: Dave Hansen <dave.hansen@intel.com>
Cc: Eric Snowberg <eric.snowberg@oracle.com>
Cc: Hans de Goede <hdegoede@redhat.com>
Cc: Joe Perches <joe@perches.com>
Cc: Jon Hunter <jonathanh@nvidia.com>
Cc: Julien Thierry <julien.thierry@arm.com>
Cc: Linus Torvalds <torvalds@linux-foundation.org>
Cc: Marc Zyngier <marc.zyngier@arm.com>
Cc: Matt Fleming <matt@codeblueprint.co.uk>
Cc: Nathan Chancellor <natechancellor@gmail.com>
Cc: Peter Zijlstra <peterz@infradead.org>
Cc: Sai Praneeth Prakhya <sai.praneeth.prakhya@intel.com>
Cc: Sedat Dilek <sedat.dilek@gmail.com>
Cc: Thomas Gleixner <tglx@linutronix.de>
Cc: linux-efi@vger.kernel.org
Link: http://lkml.kernel.org/r/20181129171230.18699-12-ard.biesheuvel@linaro.org
Signed-off-by: Ingo Molnar <mingo@kernel.org>
Signed-off-by: Sasha Levin <sashal@kernel.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 5fdacb322ceb..c3e6be110b7d 100644
--- a/arch/x86/platform/efi/early_printk.c
+++ b/arch/x86/platform/efi/early_printk.c
@@ -179,7 +179,7 @@ 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