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From: Song Liu <song@kernel.org>
To: <linux-kernel@vger.kernel.org>
Cc: <kernel-team@meta.com>, Song Liu <song@kernel.org>,
	Kees Cook <keescook@chromium.org>, <x86@kernel.org>
Subject: [PATCH] x86/vmlinux: Fix linker fill bytes for ld.lld
Date: Wed, 6 Sep 2023 10:52:15 -0700	[thread overview]
Message-ID: <20230906175215.2236033-1-song@kernel.org> (raw)

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@chromium.org>
Cc: x86@kernel.org
Signed-off-by: Song Liu <song@kernel.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


             reply	other threads:[~2023-09-06 17:52 UTC|newest]

Thread overview: 7+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2023-09-06 17:52 Song Liu [this message]
2023-09-06 18:06 ` [PATCH] x86/vmlinux: Fix linker fill bytes for ld.lld Kees Cook
2023-09-06 18:16   ` Song Liu
2023-09-06 18:27     ` Fangrui Song
2023-09-06 19:58 ` Peter Zijlstra
2023-09-06 20:02   ` Song Liu
2023-09-06 21:57 ` [tip: x86/urgent] x86/build: Fix linker fill bytes quirk/incompatibility " tip-bot2 for Song Liu

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