1 files changed, 32 insertions, 123 deletions

diff --git a/arch/arm64/kernel/kaslr.c b/arch/arm64/kernel/kaslr.c
index 47080c49cc7e..325455d16dbc 100644
--- a/arch/arm64/kernel/kaslr.c
+++ b/arch/arm64/kernel/kaslr.c
@@ -1,9 +1,6 @@
+// SPDX-License-Identifier: GPL-2.0-only
 /*
  * Copyright (C) 2016 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/cache.h>
@@ -13,74 +10,25 @@
 #include <linux/mm_types.h>
 #include <linux/sched.h>
 #include <linux/types.h>
+#include <linux/pgtable.h>
+#include <linux/random.h>
 
 #include <asm/fixmap.h>
 #include <asm/kernel-pgtable.h>
 #include <asm/memory.h>
 #include <asm/mmu.h>
-#include <asm/pgtable.h>
 #include <asm/sections.h>
+#include <asm/setup.h>
 
 u64 __ro_after_init module_alloc_base;
 u16 __initdata memstart_offset_seed;
 
-static __init u64 get_kaslr_seed(void *fdt)
-{
-	int node, len;
-	fdt64_t *prop;
-	u64 ret;
-
-	node = fdt_path_offset(fdt, "/chosen");
-	if (node < 0)
-		return 0;
-
-	prop = fdt_getprop_w(fdt, node, "kaslr-seed", &len);
-	if (!prop || len != sizeof(u64))
-		return 0;
-
-	ret = fdt64_to_cpu(*prop);
-	*prop = 0;
-	return ret;
-}
-
-static __init const u8 *get_cmdline(void *fdt)
-{
-	static __initconst const u8 default_cmdline[] = CONFIG_CMDLINE;
-
-	if (!IS_ENABLED(CONFIG_CMDLINE_FORCE)) {
-		int node;
-		const u8 *prop;
-
-		node = fdt_path_offset(fdt, "/chosen");
-		if (node < 0)
-			goto out;
-
-		prop = fdt_getprop(fdt, node, "bootargs", NULL);
-		if (!prop)
-			goto out;
-		return prop;
-	}
-out:
-	return default_cmdline;
-}
+struct arm64_ftr_override kaslr_feature_override __initdata;
 
-extern void *__init __fixmap_remap_fdt(phys_addr_t dt_phys, int *size,
-				       pgprot_t prot);
-
-/*
- * This routine will be executed with the kernel mapped at its default virtual
- * address, and if it returns successfully, the kernel will be remapped, and
- * start_kernel() will be executed from a randomized virtual offset. The
- * relocation will result in all absolute references (e.g., static variables
- * containing function pointers) to be reinitialized, and zero-initialized
- * .bss variables will be reset to 0.
- */
-u64 __init kaslr_early_init(u64 dt_phys)
+static int __init kaslr_init(void)
 {
-	void *fdt;
-	u64 seed, offset, mask, module_range;
-	const u8 *cmdline, *str;
-	int size;
+	u64 module_range;
+	u32 seed;
 
 	/*
 	 * Set a reasonable default for module_alloc_base in case
@@ -88,97 +36,58 @@ u64 __init kaslr_early_init(u64 dt_phys)
 	 */
 	module_alloc_base = (u64)_etext - MODULES_VSIZE;
 
-	/*
-	 * Try to map the FDT early. If this fails, we simply bail,
-	 * and proceed with KASLR disabled. We will make another
-	 * attempt at mapping the FDT in setup_machine()
-	 */
-	early_fixmap_init();
-	fdt = __fixmap_remap_fdt(dt_phys, &size, PAGE_KERNEL);
-	if (!fdt)
-		return 0;
-
-	/*
-	 * Retrieve (and wipe) the seed from the FDT
-	 */
-	seed = get_kaslr_seed(fdt);
-	if (!seed)
+	if (kaslr_feature_override.val & kaslr_feature_override.mask & 0xf) {
+		pr_info("KASLR disabled on command line\n");
 		return 0;
+	}
 
-	/*
-	 * Check if 'nokaslr' appears on the command line, and
-	 * return 0 if that is the case.
-	 */
-	cmdline = get_cmdline(fdt);
-	str = strstr(cmdline, "nokaslr");
-	if (str == cmdline || (str > cmdline && *(str - 1) == ' '))
+	if (!kaslr_offset()) {
+		pr_warn("KASLR disabled due to lack of seed\n");
 		return 0;
+	}
 
-	/*
-	 * OK, so we are proceeding with KASLR enabled. Calculate a suitable
-	 * kernel image offset from the seed. Let's place the kernel in the
-	 * lower half of the VMALLOC area (VA_BITS - 2).
-	 * Even if we could randomize at page granularity for 16k and 64k pages,
-	 * let's always round to 2 MB so we don't interfere with the ability to
-	 * map using contiguous PTEs
-	 */
-	mask = ((1UL << (VA_BITS - 2)) - 1) & ~(SZ_2M - 1);
-	offset = seed & mask;
-
-	/* use the top 16 bits to randomize the linear region */
-	memstart_offset_seed = seed >> 48;
+	pr_info("KASLR enabled\n");
 
 	/*
-	 * The kernel Image should not extend across a 1GB/32MB/512MB alignment
-	 * boundary (for 4KB/16KB/64KB granule kernels, respectively). If this
-	 * happens, round down the KASLR offset by (1 << SWAPPER_TABLE_SHIFT).
-	 *
-	 * NOTE: The references to _text and _end below will already take the
-	 *       modulo offset (the physical displacement modulo 2 MB) into
-	 *       account, given that the physical placement is controlled by
-	 *       the loader, and will not change as a result of the virtual
-	 *       mapping we choose.
+	 * KASAN without KASAN_VMALLOC does not expect the module region to
+	 * intersect the vmalloc region, since shadow memory is allocated for
+	 * each module at load time, whereas the vmalloc region will already be
+	 * shadowed by KASAN zero pages.
 	 */
-	if ((((u64)_text + offset) >> SWAPPER_TABLE_SHIFT) !=
-	    (((u64)_end + offset) >> SWAPPER_TABLE_SHIFT))
-		offset = round_down(offset, 1 << SWAPPER_TABLE_SHIFT);
+	BUILD_BUG_ON((IS_ENABLED(CONFIG_KASAN_GENERIC) ||
+	              IS_ENABLED(CONFIG_KASAN_SW_TAGS)) &&
+		     !IS_ENABLED(CONFIG_KASAN_VMALLOC));
 
-	if (IS_ENABLED(CONFIG_KASAN))
-		/*
-		 * KASAN does not expect the module region to intersect the
-		 * vmalloc region, since shadow memory is allocated for each
-		 * module at load time, whereas the vmalloc region is shadowed
-		 * by KASAN zero pages. So keep modules out of the vmalloc
-		 * region if KASAN is enabled.
-		 */
-		return offset;
+	seed = get_random_u32();
 
 	if (IS_ENABLED(CONFIG_RANDOMIZE_MODULE_REGION_FULL)) {
 		/*
-		 * Randomize the module region independently from the core
-		 * kernel. This prevents modules from leaking any information
+		 * 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 = VMALLOC_END - VMALLOC_START - MODULES_VSIZE;
-		module_alloc_base = VMALLOC_START;
+		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.
+		 * 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);
-		module_alloc_base = (u64)_etext + offset - MODULES_VSIZE;
 	}
 
 	/* 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 offset;
+	return 0;
 }
+subsys_initcall(kaslr_init)