linux-kernel - [PATCH] x86/vmlinux: Fix linker fill bytes for ld.lld

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Date:   Wed, 6 Sep 2023 10:52:15 -0700
From:   Song Liu <song@...nel.org>
To:     <linux-kernel@...r.kernel.org>
CC:     <kernel-team@...a.com>, Song Liu <song@...nel.org>,
        Kees Cook <keescook@...omium.org>, <x86@...nel.org>
Subject: [PATCH] x86/vmlinux: Fix linker fill bytes for ld.lld

With ":text =0xcccc", ld.lld fills unused text area with 0xcccc0000.
Example objdump -D output:

ffffffff82b04203:       00 00                   add    %al,(%rax)
ffffffff82b04205:       cc                      int3
ffffffff82b04206:       cc                      int3
ffffffff82b04207:       00 00                   add    %al,(%rax)
ffffffff82b04209:       cc                      int3
ffffffff82b0420a:       cc                      int3

Replace it with ":text =0xcccccccc", so we get the following instead:

ffffffff82b04203:       cc                      int3
ffffffff82b04204:       cc                      int3
ffffffff82b04205:       cc                      int3
ffffffff82b04206:       cc                      int3
ffffffff82b04207:       cc                      int3
ffffffff82b04208:       cc                      int3

gcc/ld doesn't seem to have the same issue. The generated code stays the
same for gcc/ld.

Cc: Kees Cook <keescook@...omium.org>
Cc: x86@...nel.org
Signed-off-by: Song Liu <song@...nel.org>
---
 arch/x86/kernel/vmlinux.lds.S | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/arch/x86/kernel/vmlinux.lds.S b/arch/x86/kernel/vmlinux.lds.S
index 83d41c2601d7..41d56fb9bf92 100644
--- a/arch/x86/kernel/vmlinux.lds.S
+++ b/arch/x86/kernel/vmlinux.lds.S
@@ -156,7 +156,7 @@ SECTIONS
 		ALIGN_ENTRY_TEXT_END
 		*(.gnu.warning)
 
-	} :text =0xcccc
+	} :text =0xcccccccc
 
 	/* End of text section, which should occupy whole number of pages */
 	_etext = .;
-- 
2.34.1