linux-kernel - [tip: x86/urgent] x86/build: Fix linker fill bytes quirk/incompatibility for ld.lld

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Message-ID: <169403743756.27769.4802517361429397352.tip-bot2@tip-bot2>
Date:   Wed, 06 Sep 2023 21:57:17 -0000
From:   "tip-bot2 for Song Liu" <tip-bot2@...utronix.de>
To:     linux-tip-commits@...r.kernel.org
Cc:     Song Liu <song@...nel.org>, Ingo Molnar <mingo@...nel.org>,
        Kees Cook <keescook@...omium.org>,
        "Peter Zijlstra (Intel)" <peterz@...radead.org>, x86@...nel.org,
        linux-kernel@...r.kernel.org
Subject: [tip: x86/urgent] x86/build: Fix linker fill bytes
 quirk/incompatibility for ld.lld

The following commit has been merged into the x86/urgent branch of tip:

Commit-ID:     65e710899fd19f435f40268f3a92dfaa11f14470
Gitweb:        https://git.kernel.org/tip/65e710899fd19f435f40268f3a92dfaa11f14470
Author:        Song Liu <song@...nel.org>
AuthorDate:    Wed, 06 Sep 2023 10:52:15 -07:00
Committer:     Ingo Molnar <mingo@...nel.org>
CommitterDate: Wed, 06 Sep 2023 23:49:12 +02:00

x86/build: Fix linker fill bytes quirk/incompatibility 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.

Signed-off-by: Song Liu <song@...nel.org>
Signed-off-by: Ingo Molnar <mingo@...nel.org>
Reviewed-by: Kees Cook <keescook@...omium.org>
Acked-by: Peter Zijlstra (Intel) <peterz@...radead.org>
Fixes: 7705dc855797 ("x86/vmlinux: Use INT3 instead of NOP for linker fill bytes")
Link: https://lore.kernel.org/r/20230906175215.2236033-1-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 83d41c2..f15fb71 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 = .;