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From:   Evgeniy Baskov <baskov@ispras.ru>
To:     Ard Biesheuvel <ardb@kernel.org>
Cc:     Evgeniy Baskov <baskov@ispras.ru>, Borislav Petkov <bp@alien8.de>,
        Andy Lutomirski <luto@kernel.org>,
        Dave Hansen <dave.hansen@linux.intel.com>,
        Ingo Molnar <mingo@redhat.com>,
        Peter Zijlstra <peterz@infradead.org>,
        Thomas Gleixner <tglx@linutronix.de>,
        Alexey Khoroshilov <khoroshilov@ispras.ru>,
        Peter Jones <pjones@redhat.com>,
        "Limonciello, Mario" <mario.limonciello@amd.com>,
        joeyli <jlee@suse.com>, lvc-project@linuxtesting.org,
        x86@kernel.org, linux-efi@vger.kernel.org,
        linux-kernel@vger.kernel.org, linux-hardening@vger.kernel.org
Subject: [PATCH v4 17/26] x86/boot: Reduce size of the DOS stub
Date:   Thu, 15 Dec 2022 15:38:08 +0300
Message-Id: <cb62472011a0c4151276b6a05b83b60b1bf6f352.1671098103.git.baskov@ispras.ru>
In-Reply-To: <cover.1671098103.git.baskov@ispras.ru>
References: <cover.1671098103.git.baskov@ispras.ru>
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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.

Tested-by: Mario Limonciello <mario.limonciello@amd.com>
Tested-by: Peter Jones <pjones@redhat.com>
Signed-off-by: Evgeniy Baskov <baskov@ispras.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 9338c68e7413..9fec80bc504b 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
@@ -90,10 +89,9 @@ 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