arm64: module: move module randomization to module.c

When CONFIG_RANDOMIZE_BASE=y, module_alloc_base is a variable which is
configured by kaslr_module_init() in kaslr.c, and otherwise it is an
expression defined in module.h.

As kaslr_module_init() is no longer tightly coupled with the KASLR
initialization code, we can centralize this in module.c.

This patch moves kaslr_module_init() to module.c, making
module_alloc_base a static variable, and removing redundant includes from
kaslr.c. For the defintion of struct arm64_ftr_override we must include
<asm/cpufeature.h>, which was previously included transitively via
another header.

There should be no functional change as a result of this patch.

Signed-off-by: Mark Rutland <mark.rutland@arm.com>
Reviewed-by: Ard Biesheuvel <ardb@kernel.org>
Cc: Will Deacon <will@kernel.org>
Tested-by: Shanker Donthineni <sdonthineni@nvidia.com>
Link: https://lore.kernel.org/r/20230530110328.2213762-5-mark.rutland@arm.com
Signed-off-by: Catalin Marinas <catalin.marinas@arm.com>

Author: mrutland-arm

arch/arm64/include/asm/module.h

@@ -30,12 +30,6 @@ u64 module_emit_plt_entry(struct module *mod, Elf64_Shdr *sechdrs,
 u64 module_emit_veneer_for_adrp(struct module *mod, Elf64_Shdr *sechdrs,
 				void *loc, u64 val);
 
-#ifdef CONFIG_RANDOMIZE_BASE
-extern u64 module_alloc_base;
-#else
-#define module_alloc_base	((u64)_etext - MODULES_VSIZE)
-#endif
-
 struct plt_entry {
 	/*
 	 * A program that conforms to the AArch64 Procedure Call Standard

arch/arm64/kernel/kaslr.c

@@ -4,23 +4,12 @@
  */
 
 #include <linux/cache.h>
-#include <linux/crc32.h>
 #include <linux/init.h>
-#include <linux/libfdt.h>
-#include <linux/mm_types.h>
-#include <linux/sched.h>
-#include <linux/types.h>
-#include <linux/pgtable.h>
-#include <linux/random.h>
+#include <linux/printk.h>
 
-#include <asm/fixmap.h>
-#include <asm/kernel-pgtable.h>
+#include <asm/cpufeature.h>
 #include <asm/memory.h>
-#include <asm/mmu.h>
-#include <asm/sections.h>
-#include <asm/setup.h>
 
-u64 __ro_after_init module_alloc_base;
 u16 __initdata memstart_offset_seed;
 
 struct arm64_ftr_override kaslr_feature_override __initdata;
@@ -47,48 +36,3 @@ void __init kaslr_init(void)
 	pr_info("KASLR enabled\n");
 	__kaslr_is_enabled = true;
 }
-
-int kaslr_module_init(void)
-{
-	u64 module_range;
-	u32 seed;
-
-	/*
-	 * Set a reasonable default for module_alloc_base in case
-	 * we end up running with module randomization disabled.
-	 */
-	module_alloc_base = (u64)_etext - MODULES_VSIZE;
-
-	seed = get_random_u32();
-
-	if (IS_ENABLED(CONFIG_RANDOMIZE_MODULE_REGION_FULL)) {
-		/*
-		 * Randomize the module region over a 2 GB window covering the
-		 * kernel. This reduces the risk of modules leaking information
-		 * about the address of the kernel itself, but results in
-		 * branches between modules and the core kernel that are
-		 * resolved via PLTs. (Branches between modules will be
-		 * resolved normally.)
-		 */
-		module_range = SZ_2G - (u64)(_end - _stext);
-		module_alloc_base = max((u64)_end - SZ_2G, (u64)MODULES_VADDR);
-	} else {
-		/*
-		 * Randomize the module region by setting module_alloc_base to
-		 * a PAGE_SIZE multiple in the range [_etext - MODULES_VSIZE,
-		 * _stext) . This guarantees that the resulting region still
-		 * covers [_stext, _etext], and that all relative branches can
-		 * be resolved without veneers unless this region is exhausted
-		 * and we fall back to a larger 2GB window in module_alloc()
-		 * when ARM64_MODULE_PLTS is enabled.
-		 */
-		module_range = MODULES_VSIZE - (u64)(_etext - _stext);
-	}
-
-	/* use the lower 21 bits to randomize the base of the module region */
-	module_alloc_base += (module_range * (seed & ((1 << 21) - 1))) >> 21;
-	module_alloc_base &= PAGE_MASK;
-
-	return 0;
-}
-subsys_initcall(kaslr_module_init)

arch/arm64/kernel/module.c

@@ -15,13 +15,61 @@
 #include <linux/kernel.h>
 #include <linux/mm.h>
 #include <linux/moduleloader.h>
+#include <linux/random.h>
 #include <linux/scs.h>
 #include <linux/vmalloc.h>
+
 #include <asm/alternative.h>
 #include <asm/insn.h>
 #include <asm/scs.h>
 #include <asm/sections.h>
 
+static u64 __ro_after_init module_alloc_base = (u64)_etext - MODULES_VSIZE;
+
+#ifdef CONFIG_RANDOMIZE_BASE
+static int __init kaslr_module_init(void)
+{
+	u64 module_range;
+	u32 seed;
+
+	if (!kaslr_enabled())
+		return 0;
+
+	seed = get_random_u32();
+
+	if (IS_ENABLED(CONFIG_RANDOMIZE_MODULE_REGION_FULL)) {
+		/*
+		 * Randomize the module region over a 2 GB window covering the
+		 * kernel. This reduces the risk of modules leaking information
+		 * about the address of the kernel itself, but results in
+		 * branches between modules and the core kernel that are
+		 * resolved via PLTs. (Branches between modules will be
+		 * resolved normally.)
+		 */
+		module_range = SZ_2G - (u64)(_end - _stext);
+		module_alloc_base = max((u64)_end - SZ_2G, (u64)MODULES_VADDR);
+	} else {
+		/*
+		 * Randomize the module region by setting module_alloc_base to
+		 * a PAGE_SIZE multiple in the range [_etext - MODULES_VSIZE,
+		 * _stext) . This guarantees that the resulting region still
+		 * covers [_stext, _etext], and that all relative branches can
+		 * be resolved without veneers unless this region is exhausted
+		 * and we fall back to a larger 2GB window in module_alloc()
+		 * when ARM64_MODULE_PLTS is enabled.
+		 */
+		module_range = MODULES_VSIZE - (u64)(_etext - _stext);
+	}
+
+	/* use the lower 21 bits to randomize the base of the module region */
+	module_alloc_base += (module_range * (seed & ((1 << 21) - 1))) >> 21;
+	module_alloc_base &= PAGE_MASK;
+
+	return 0;
+}
+subsys_initcall(kaslr_module_init)
+#endif
+
 void *module_alloc(unsigned long size)
 {
 	u64 module_alloc_end = module_alloc_base + MODULES_VSIZE;