linux-kernel - [PATCH 2.6.23-rc1] APM detection logic bug fix

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-next>] [day] [month] [year] [list]

Message-Id: <200707232225.l6NMPxrq009114@harpo.it.uu.se>
Date:	Tue, 24 Jul 2007 00:25:59 +0200 (MEST)
From:	Mikael Pettersson <mikpe@...uu.se>
To:	linux-kernel@...r.kernel.org
Cc:	"H. Peter Anvin" <hpa@...or.com>
Subject: [PATCH 2.6.23-rc1] APM detection logic bug fix

Starting with kernel 2.6.23-rc1, the i386 APM driver fails
on several of my machines with the message:

apm: BIOS not found

This happens because of a bug in the i386 boot code rewrite
from assembler to C. The original assembly code had the
following code in its APM BIOS presence test (boot/setup.S):

	andw	$0x02, %cx			# Is 32 bit supported?
	je	done_apm_bios			# No 32-bit, no (good) APM BIOS

That is, the code bails out if bit 2 is zero.

In the new C version, this is coded as (boot/apm.c):

	if (cx & 0x02)		/* 32 bits supported? */
		return -1;

Here we see that the test has been accidentally inverted.

The fix is to negate the test. I've verified that this
allows the APM driver to work again on my affected machines.

Signed-off-by: Mikael Pettersson <mikpe@...uu.se>

diff -rupN linux-2.6.23-rc1/arch/i386/boot/apm.c linux-2.6.23-rc1.apm-detect-fix/arch/i386/boot/apm.c
--- linux-2.6.23-rc1/arch/i386/boot/apm.c	2007-07-23 02:32:03.000000000 +0200
+++ linux-2.6.23-rc1.apm-detect-fix/arch/i386/boot/apm.c	2007-07-23 23:51:17.000000000 +0200
@@ -40,7 +40,7 @@ int query_apm_bios(void)
 	if (bx != 0x504d)	/* "PM" signature */
 		return -1;

-	if (cx & 0x02)		/* 32 bits supported? */
+	if (!(cx & 0x02))		/* 32 bits supported? */
 		return -1;

 	/* Disconnect first, just in case */
-
To unsubscribe from this list: send the line "unsubscribe linux-kernel" in
the body of a message to majordomo@...r.kernel.org
More majordomo info at  http://vger.kernel.org/majordomo-info.html
Please read the FAQ at  http://www.tux.org/lkml/