This adds support for emitting PLTs at module load time for relative
branches that are out of range. This is a prerequisite for KASLR, which
may place the kernel and the modules anywhere in the vmalloc area,
making it more likely that branch target offsets exceed the maximum
range of +/- 128 MB.

Signed-off-by: Ard Biesheuvel <redacted>
---
 arch/arm64/Kconfig              |   9 ++
 arch/arm64/Makefile             |   6 +-
 arch/arm64/include/asm/module.h |  11 ++
 arch/arm64/kernel/Makefile      |   1 +
 arch/arm64/kernel/module-plts.c | 137 ++++++++++++++++++++
 arch/arm64/kernel/module.c      |  12 ++
 arch/arm64/kernel/module.lds    |   4 +
 7 files changed, 179 insertions(+), 1 deletion(-)

diff --git a/arch/arm64/Kconfig b/arch/arm64/Kconfig
index ffa3c549a4ba..778df20bf623 100644
--- a/arch/arm64/Kconfig
+++ b/arch/arm64/Kconfig

@@ -363,6 +363,7 @@ config ARM64_ERRATUM_843419
 	bool "Cortex-A53: 843419: A load or store might access an incorrect address"
 	depends on MODULES
 	default y
+	select ARM64_MODULE_CMODEL_LARGE
 	help
 	  This option builds kernel modules using the large memory model in
 	  order to avoid the use of the ADRP instruction, which can cause

@@ -702,6 +703,14 @@ config ARM64_LSE_ATOMICS
 
 endmenu
 
+config ARM64_MODULE_CMODEL_LARGE
+	bool
+
+config ARM64_MODULE_PLTS
+	bool
+	select ARM64_MODULE_CMODEL_LARGE
+	select HAVE_MOD_ARCH_SPECIFIC
+
 endmenu
 
 menu "Boot options"

diff --git a/arch/arm64/Makefile b/arch/arm64/Makefile
index cd822d8454c0..db462980c6be 100644
--- a/arch/arm64/Makefile
+++ b/arch/arm64/Makefile

@@ -41,10 +41,14 @@ endif
 
 CHECKFLAGS	+= -D__aarch64__
 
-ifeq ($(CONFIG_ARM64_ERRATUM_843419), y)
+ifeq ($(CONFIG_ARM64_MODULE_CMODEL_LARGE), y)
 KBUILD_CFLAGS_MODULE	+= -mcmodel=large
 endif
 
+ifeq ($(CONFIG_ARM64_MODULE_PLTS),y)
+KBUILD_LDFLAGS_MODULE	+= -T $(srctree)/arch/arm64/kernel/module.lds
+endif
+
 # Default value
 head-y		:= arch/arm64/kernel/head.o
 

diff --git a/arch/arm64/include/asm/module.h b/arch/arm64/include/asm/module.h
index e80e232b730e..7b8cd3dc9d8e 100644
--- a/arch/arm64/include/asm/module.h
+++ b/arch/arm64/include/asm/module.h

@@ -20,4 +20,15 @@
 
 #define MODULE_ARCH_VERMAGIC	"aarch64"
 
+#ifdef CONFIG_ARM64_MODULE_PLTS
+struct mod_arch_specific {
+	struct elf64_shdr	*core_plt;
+	struct elf64_shdr	*init_plt;
+	int			core_plt_count;
+	int			init_plt_count;
+};
+#endif
+
+u64 get_module_plt(struct module *mod, void *loc, u64 val);
+
 #endif /* __ASM_MODULE_H */

diff --git a/arch/arm64/kernel/Makefile b/arch/arm64/kernel/Makefile
index 474691f8b13a..f42b0fff607f 100644
--- a/arch/arm64/kernel/Makefile
+++ b/arch/arm64/kernel/Makefile

@@ -30,6 +30,7 @@ arm64-obj-$(CONFIG_COMPAT)		+= sys32.o kuser32.o signal32.o 	\
 					   ../../arm/kernel/opcodes.o
 arm64-obj-$(CONFIG_FUNCTION_TRACER)	+= ftrace.o entry-ftrace.o
 arm64-obj-$(CONFIG_MODULES)		+= arm64ksyms.o module.o
+arm64-obj-$(CONFIG_ARM64_MODULE_PLTS)	+= module-plts.o
 arm64-obj-$(CONFIG_PERF_EVENTS)		+= perf_regs.o perf_callchain.o
 arm64-obj-$(CONFIG_HW_PERF_EVENTS)	+= perf_event.o
 arm64-obj-$(CONFIG_HAVE_HW_BREAKPOINT)	+= hw_breakpoint.o

diff --git a/arch/arm64/kernel/module-plts.c b/arch/arm64/kernel/module-plts.c
new file mode 100644
index 000000000000..4a8ef9ea01ee
--- /dev/null
+++ b/arch/arm64/kernel/module-plts.c

@@ -0,0 +1,137 @@
+/*
+ * Copyright (C) 2014-2015 Linaro Ltd. <ard.biesheuvel@linaro.org>
+ *
+ * This program is free software; you can redistribute it and/or modify
+ * it under the terms of the GNU General Public License version 2 as
+ * published by the Free Software Foundation.
+ */
+
+#include <linux/elf.h>
+#include <linux/kernel.h>
+#include <linux/module.h>
+
+struct plt_entry {
+	__le32	mov0;	/* movn	x16, #0x....			*/
+	__le32	mov1;	/* movk	x16, #0x...., lsl #16		*/
+	__le32	mov2;	/* movk	x16, #0x...., lsl #32		*/
+	__le32	br;	/* br	x16				*/
+} __aligned(8);

+
+		if (strstr(secstrings + s->sh_name, ".init"))
+			init_plts += count_plts(dstsec->sh_addr, rels, numrels);
+		else
+			core_plts += count_plts(dstsec->sh_addr, rels, numrels);
+	}
+
+	mod->arch.core_plt->sh_type = SHT_NOBITS;
+	mod->arch.core_plt->sh_flags = SHF_EXECINSTR | SHF_ALLOC;
+	mod->arch.core_plt->sh_addralign = L1_CACHE_BYTES;
+	mod->arch.core_plt->sh_size = core_plts * sizeof(struct plt_entry);
+	mod->arch.core_plt_count = 0;
+
+	mod->arch.init_plt->sh_type = SHT_NOBITS;
+	mod->arch.init_plt->sh_flags = SHF_EXECINSTR | SHF_ALLOC;
+	mod->arch.init_plt->sh_addralign = L1_CACHE_BYTES;
+	mod->arch.init_plt->sh_size = init_plts * sizeof(struct plt_entry);
+	mod->arch.init_plt_count = 0;
+	pr_debug("%s: core.plt=%lld, init.plt=%lld\n", __func__,
+		 mod->arch.core_plt->sh_size, mod->arch.init_plt->sh_size);
+	return 0;
+}

diff --git a/arch/arm64/kernel/module.c b/arch/arm64/kernel/module.c
index 93e970231ca9..3a298b0e21bb 100644
--- a/arch/arm64/kernel/module.c
+++ b/arch/arm64/kernel/module.c

@@ -38,6 +38,11 @@ void *module_alloc(unsigned long size)
 				GFP_KERNEL, PAGE_KERNEL_EXEC, 0,
 				NUMA_NO_NODE, __builtin_return_address(0));
 
+	if (!p && IS_ENABLED(CONFIG_ARM64_MODULE_PLTS))
+		p = __vmalloc_node_range(size, MODULE_ALIGN, VMALLOC_START,
+				VMALLOC_END, GFP_KERNEL, PAGE_KERNEL_EXEC, 0,
+				NUMA_NO_NODE, __builtin_return_address(0));
+
 	if (p && (kasan_module_alloc(p, size) < 0)) {
 		vfree(p);
 		return NULL;

@@ -361,6 +366,13 @@ int apply_relocate_add(Elf64_Shdr *sechdrs,
 		case R_AARCH64_CALL26:
 			ovf = reloc_insn_imm(RELOC_OP_PREL, loc, val, 2, 26,
 					     AARCH64_INSN_IMM_26);
+
+			if (IS_ENABLED(CONFIG_ARM64_MODULE_PLTS) &&
+			    ovf == -ERANGE) {
+				val = get_module_plt(me, loc, val);
+				ovf = reloc_insn_imm(RELOC_OP_PREL, loc, val, 2,
+						     26, AARCH64_INSN_IMM_26);
+			}
 			break;
 
 		default:

diff --git a/arch/arm64/kernel/module.lds b/arch/arm64/kernel/module.lds
new file mode 100644
index 000000000000..3682fa107918
--- /dev/null
+++ b/arch/arm64/kernel/module.lds

@@ -0,0 +1,4 @@
+SECTIONS {
+        .core.plt : { BYTE(0) }
+        .init.plt : { BYTE(0) }
+}

-- 
2.5.0