linux-kernel - [PATCH v6 24/27] x86/mm: Make the x86 GOT read-only

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Message-Id: <20190131192533.34130-25-thgarnie@chromium.org>
Date:   Thu, 31 Jan 2019 11:24:31 -0800
From:   Thomas Garnier <thgarnie@...omium.org>
To:     kernel-hardening@...ts.openwall.com
Cc:     kristen@...ux.intel.com, Thomas Garnier <thgarnie@...omium.org>,
        Arnd Bergmann <arnd@...db.de>, linux-arch@...r.kernel.org,
        linux-kernel@...r.kernel.org
Subject: [PATCH v6 24/27] x86/mm: Make the x86 GOT read-only

The GOT is changed during early boot when relocations are applied. Make
it read-only directly. This table exists only for PIE binary.

Position Independent Executable (PIE) support will allow to extend the
KASLR randomization range below 0xffffffff80000000.

Signed-off-by: Thomas Garnier <thgarnie@...omium.org>
---
 include/asm-generic/vmlinux.lds.h | 12 ++++++++++++
 1 file changed, 12 insertions(+)

diff --git a/include/asm-generic/vmlinux.lds.h b/include/asm-generic/vmlinux.lds.h
index 3d7a6a9c2370..0a038594c878 100644
--- a/include/asm-generic/vmlinux.lds.h
+++ b/include/asm-generic/vmlinux.lds.h
@@ -323,6 +323,17 @@
 	__end_ro_after_init = .;
 #endif
 
+#ifdef CONFIG_X86_PIE
+#define RO_GOT_X86							\
+	.got        : AT(ADDR(.got) - LOAD_OFFSET) {			\
+		__start_got = .;					\
+		*(.got);						\
+		__end_got = .;						\
+	}
+#else
+#define RO_GOT_X86
+#endif
+
 /*
  * Read only Data
  */
@@ -379,6 +390,7 @@
 		__end_builtin_fw = .;					\
 	}								\
 									\
+	RO_GOT_X86							\
 	TRACEDATA							\
 									\
 	/* Kernel symbol table: Normal symbols */			\
-- 
2.20.1.495.gaa96b0ce6b-goog