linux-hardening - [PATCH v2 17/23] x86/boot: Reduce size of the DOS stub

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 PHC
Open Source and information security mailing list archives

Hash Suite: Windows password security audit tool. GUI, reports in PDF.

[<prev] [next>] [<thread-prev] [thread-next>] [day] [month] [year] [list]

Date:   Tue, 25 Oct 2022 17:12:55 +0300
From:   Evgeniy Baskov <baskov@...ras.ru>
To:     Ard Biesheuvel <ardb@...nel.org>
Cc:     Evgeniy Baskov <baskov@...ras.ru>, Borislav Petkov <bp@...en8.de>,
        Andy Lutomirski <luto@...nel.org>,
        Dave Hansen <dave.hansen@...ux.intel.com>,
        Ingo Molnar <mingo@...hat.com>,
        Peter Zijlstra <peterz@...radead.org>,
        Thomas Gleixner <tglx@...utronix.de>,
        Alexey Khoroshilov <khoroshilov@...ras.ru>,
        Peter Jones <pjones@...hat.com>, lvc-project@...uxtesting.org,
        x86@...nel.org, linux-efi@...r.kernel.org,
        linux-kernel@...r.kernel.org, linux-hardening@...r.kernel.org
Subject: [PATCH v2 17/23] x86/boot: Reduce size of the DOS stub

This is required to fit more sections in PE section tables,
since its size is restricted by zero page located at specific offset
after the PE header.

Signed-off-by: Evgeniy Baskov <baskov@...ras.ru>
---
 arch/x86/boot/header.S | 14 ++++++--------
 1 file changed, 6 insertions(+), 8 deletions(-)

diff --git a/arch/x86/boot/header.S b/arch/x86/boot/header.S
index f912d7770130..e4de831b2f64 100644
--- a/arch/x86/boot/header.S
+++ b/arch/x86/boot/header.S
@@ -59,17 +59,16 @@ start2:
 	cld
 
 	movw	$bugger_off_msg, %si
+	movw	$bugger_off_msg_size, %cx
 
 msg_loop:
 	lodsb
-	andb	%al, %al
-	jz	bs_die
 	movb	$0xe, %ah
 	movw	$7, %bx
 	int	$0x10
-	jmp	msg_loop
+	decw	%cx
+	jnz	msg_loop
 
-bs_die:
 	# Allow the user to press a key, then reboot
 	xorw	%ax, %ax
 	int	$0x16
@@ -89,10 +88,9 @@ bs_die:
 
 	.section ".bsdata", "a"
 bugger_off_msg:
-	.ascii	"Use a boot loader.\r\n"
-	.ascii	"\n"
-	.ascii	"Remove disk and press any key to reboot...\r\n"
-	.byte	0
+	.ascii	"Use a boot loader. "
+	.ascii	"Press a key to reboot"
+	.set	bugger_off_msg_size, . - bugger_off_msg
 
 #ifdef CONFIG_EFI_STUB
 pe_header:
-- 
2.37.4