linux-kernel - [PATCH] x86/build: Move _etext to actual end of .text

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Message-ID: <20190423183827.GA4012@beast>
Date:   Tue, 23 Apr 2019 11:38:27 -0700
From:   Kees Cook <keescook@...omium.org>
To:     Borislav Petkov <bp@...e.de>
Cc:     Sami Tolvanen <samitolvanen@...gle.com>,
        linux-kernel@...r.kernel.org, x86@...nel.org
Subject: [PATCH] x86/build: Move _etext to actual end of .text

When building x86 with Clang LTO and CFI, CFI jump regions are
automatically added to the end of the .text section late in linking. As a
result, the _etext position was being labelled before the appended jump
regions, causing confusion about where the boundaries of the executable
region actually are in the running kernel, and broke at least the fault
injection code. This moves the _etext mark to outside (and immediately
after) the .text area, as it already the case on other architectures
(e.g. arm64, arm).

Reported-and-tested-by: Sami Tolvanen <samitolvanen@...gle.com>
Signed-off-by: Kees Cook <keescook@...omium.org>
---
 arch/x86/kernel/vmlinux.lds.S | 6 +++---
 1 file changed, 3 insertions(+), 3 deletions(-)

diff --git a/arch/x86/kernel/vmlinux.lds.S b/arch/x86/kernel/vmlinux.lds.S
index bad8c51fee6e..de94da2366e7 100644
--- a/arch/x86/kernel/vmlinux.lds.S
+++ b/arch/x86/kernel/vmlinux.lds.S
@@ -141,11 +141,11 @@ SECTIONS
 		*(.text.__x86.indirect_thunk)
 		__indirect_thunk_end = .;
 #endif
-
-		/* End of text section */
-		_etext = .;
 	} :text = 0x9090

+	/* End of text section */
+	_etext = .;
+
 	NOTES :text :note

 	EXCEPTION_TABLE(16) :text = 0x9090
-- 
2.17.1

-- 
Kees Cook