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List:       linux-kernel
Subject:    [PATCH v5 29/36] x86/build: Enforce an empty .got.plt section
From:       Kees Cook <keescook () chromium ! org>
Date:       2020-07-31 23:08:13
Message-ID: 20200731230820.1742553-30-keescook () chromium ! org
[Download RAW message or body]

The .got.plt section should always be zero (or filled only with the
linker-generated lazy dispatch entry). Enforce this with an assert and
mark the section as NOLOAD. This is more sensitive than just blindly
discarding the section.

Signed-off-by: Kees Cook <keescook@chromium.org>
---
 arch/x86/kernel/vmlinux.lds.S | 14 +++++++++++++-
 1 file changed, 13 insertions(+), 1 deletion(-)

diff --git a/arch/x86/kernel/vmlinux.lds.S b/arch/x86/kernel/vmlinux.lds.S
index 0cc035cb15f1..7faffe7414d6 100644
--- a/arch/x86/kernel/vmlinux.lds.S
+++ b/arch/x86/kernel/vmlinux.lds.S
@@ -414,8 +414,20 @@ SECTIONS
 	ELF_DETAILS
 
 	DISCARDS
-}
 
+	/*
+	 * Make sure that the .got.plt is either completely empty or it
+	 * contains only the lazy dispatch entries.
+	 */
+	.got.plt (NOLOAD) : { *(.got.plt) }
+	ASSERT(SIZEOF(.got.plt) == 0 ||
+#ifdef CONFIG_X86_64
+	       SIZEOF(.got.plt) == 0x18,
+#else
+	       SIZEOF(.got.plt) == 0xc,
+#endif
+	       "Unexpected GOT/PLT entries detected!")
+}
 
 #ifdef CONFIG_X86_32
 /*
-- 
2.25.1

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