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Date: Tue, 15 Jan 2019 14:02:13 -0500
From: Ruslan Nikolaev <nruslan_devel@...oo.com>
To: kernel-hardening@...ts.openwall.com
Cc: thgarnie@...gle.com, x86@...nel.org, kstewart@...uxfoundation.org,
gregkh@...uxfoundation.org, keescook@...omium.org
Subject: [PATCH v1 05/06]: Retpoline thunks for PIC modules
Retpoline thunks for PIC modules
The patch is by Hassan Nadeem and Ruslan Nikolaev. This extends
the prior PIE kernel patch (by Thomas Garnier) to also support
position-independent modules that can be placed anywhere in the
48/64-bit address space (for better KASLR).
Signed-off-by: Ruslan Nikolaev <nruslan_devel@...oo.com>
---
Makefile | 3 +++
retpoline.S | 47 +++++++++++++++++++++++++++++++++++++++++++++++
2 files changed, 50 insertions(+)
diff -uprN a/arch/x86/module-lib/Makefile b/arch/x86/module-lib/Makefile
--- a/arch/x86/module-lib/Makefile 1969-12-31 19:00:00.000000000 -0500
+++ b/arch/x86/module-lib/Makefile 2019-01-15 11:32:46.721911879 -0500
@@ -0,0 +1,3 @@
+# SPDX-License-Identifier: GPL-2.0
+
+obj-$(CONFIG_RETPOLINE) += retpoline.o
\ No newline at end of file
diff -uprN a/arch/x86/module-lib/retpoline.S
b/arch/x86/module-lib/retpoline.S
--- a/arch/x86/module-lib/retpoline.S 1969-12-31 19:00:00.000000000 -0500
+++ b/arch/x86/module-lib/retpoline.S 2019-01-15 11:32:46.721911879 -0500
@@ -0,0 +1,47 @@
+/* SPDX-License-Identifier: GPL-2.0 */
+
+#include <linux/stringify.h>
+#include <linux/linkage.h>
+#include <asm/dwarf2.h>
+#include <asm/cpufeatures.h>
+#include <asm/alternative-asm.h>
+#include <asm/export.h>
+#include <asm/nospec-branch.h>
+
+.macro THUNK reg
+ .section .text.__x86.indirect_thunk
+
+ENTRY(__x86_indirect_thunk_\reg)
+ CFI_STARTPROC
+ JMP_NOSPEC %\reg
+ CFI_ENDPROC
+ENDPROC(__x86_indirect_thunk_\reg)
+.endm
+
+/*
+ * Despite being an assembler file we can't just use .irp here
+ * because __KSYM_DEPS__ only uses the C preprocessor and would
+ * only see one instance of "__x86_indirect_thunk_\reg" rather
+ * than one per register with the correct names. So we do it
+ * the simple and nasty way...
+ */
+#define GENERATE_THUNK(reg) THUNK reg
+
+GENERATE_THUNK(_ASM_AX)
+GENERATE_THUNK(_ASM_BX)
+GENERATE_THUNK(_ASM_CX)
+GENERATE_THUNK(_ASM_DX)
+GENERATE_THUNK(_ASM_SI)
+GENERATE_THUNK(_ASM_DI)
+GENERATE_THUNK(_ASM_BP)
+#ifdef CONFIG_64BIT
+GENERATE_THUNK(r8)
+GENERATE_THUNK(r9)
+GENERATE_THUNK(r10)
+GENERATE_THUNK(r11)
+GENERATE_THUNK(r12)
+GENERATE_THUNK(r13)
+GENERATE_THUNK(r14)
+GENERATE_THUNK(r15)
+#endif
+
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