summaryrefslogtreecommitdiff
path: root/arch/arm64/kernel/kaslr.c
diff options
context:
space:
mode:
Diffstat (limited to 'arch/arm64/kernel/kaslr.c')
-rw-r--r--arch/arm64/kernel/kaslr.c203
1 files changed, 20 insertions, 183 deletions
diff --git a/arch/arm64/kernel/kaslr.c b/arch/arm64/kernel/kaslr.c
index 2a11a962e571..12c7f3c8ba76 100644
--- a/arch/arm64/kernel/kaslr.c
+++ b/arch/arm64/kernel/kaslr.c
@@ -4,205 +4,42 @@
*/
#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/printk.h>
-#include <asm/cacheflush.h>
-#include <asm/fixmap.h>
-#include <asm/kernel-pgtable.h>
+#include <asm/cpufeature.h>
#include <asm/memory.h>
-#include <asm/mmu.h>
-#include <asm/pgtable.h>
-#include <asm/sections.h>
-enum kaslr_status {
- KASLR_ENABLED,
- KASLR_DISABLED_CMDLINE,
- KASLR_DISABLED_NO_SEED,
- KASLR_DISABLED_FDT_REMAP,
-};
-
-static enum kaslr_status __initdata kaslr_status;
-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;
-}
+bool __ro_after_init __kaslr_is_enabled = false;
-static __init const u8 *kaslr_get_cmdline(void *fdt)
+void __init kaslr_init(void)
{
- 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;
-}
-
-/*
- * 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)
-{
- void *fdt;
- u64 seed, offset, mask, module_range;
- const u8 *cmdline, *str;
- int size;
-
- /*
- * 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;
- __flush_dcache_area(&module_alloc_base, sizeof(module_alloc_base));
-
- /*
- * 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) {
- kaslr_status = KASLR_DISABLED_FDT_REMAP;
- return 0;
- }
-
- /*
- * Retrieve (and wipe) the seed from the FDT
- */
- seed = get_kaslr_seed(fdt);
-
- /*
- * Check if 'nokaslr' appears on the command line, and
- * return 0 if that is the case.
- */
- cmdline = kaslr_get_cmdline(fdt);
- str = strstr(cmdline, "nokaslr");
- if (str == cmdline || (str > cmdline && *(str - 1) == ' ')) {
- kaslr_status = KASLR_DISABLED_CMDLINE;
- return 0;
- }
-
- if (!seed) {
- kaslr_status = KASLR_DISABLED_NO_SEED;
- return 0;
+ if (cpuid_feature_extract_unsigned_field(arm64_sw_feature_override.val &
+ arm64_sw_feature_override.mask,
+ ARM64_SW_FEATURE_OVERRIDE_NOKASLR)) {
+ pr_info("KASLR disabled on command line\n");
+ return;
}
/*
- * OK, so we are proceeding with KASLR enabled. Calculate a suitable
- * kernel image offset from the seed. Let's place the kernel in the
- * middle half of the VMALLOC area (VA_BITS_MIN - 2), and stay clear of
- * the lower and upper quarters to avoid colliding with other
- * allocations.
- * 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
+ * The KASLR offset modulo MIN_KIMG_ALIGN is taken from the physical
+ * placement of the image rather than from the seed, so a displacement
+ * of less than MIN_KIMG_ALIGN means that no seed was provided.
*/
- mask = ((1UL << (VA_BITS_MIN - 2)) - 1) & ~(SZ_2M - 1);
- offset = BIT(VA_BITS_MIN - 3) + (seed & mask);
-
- /* use the top 16 bits to randomize the linear region */
- memstart_offset_seed = seed >> 48;
-
- 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, and put the kernel well within
- * 4 GB of the module region.
- */
- return offset % SZ_2G;
-
- 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 + offset - 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.
- */
- module_range = MODULES_VSIZE - (u64)(_etext - _stext);
- module_alloc_base = (u64)_etext + offset - MODULES_VSIZE;
+ if (kaslr_offset() < MIN_KIMG_ALIGN) {
+ pr_warn("KASLR disabled due to lack of seed\n");
+ return;
}
- /* 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;
-
- __flush_dcache_area(&module_alloc_base, sizeof(module_alloc_base));
- __flush_dcache_area(&memstart_offset_seed, sizeof(memstart_offset_seed));
-
- return offset;
+ pr_info("KASLR enabled\n");
+ __kaslr_is_enabled = true;
}
-static int __init kaslr_init(void)
+static int __init parse_nokaslr(char *unused)
{
- switch (kaslr_status) {
- case KASLR_ENABLED:
- pr_info("KASLR enabled\n");
- break;
- case KASLR_DISABLED_CMDLINE:
- pr_info("KASLR disabled on command line\n");
- break;
- case KASLR_DISABLED_NO_SEED:
- pr_warn("KASLR disabled due to lack of seed\n");
- break;
- case KASLR_DISABLED_FDT_REMAP:
- pr_warn("KASLR disabled due to FDT remapping failure\n");
- break;
- }
-
+ /* nokaslr param handling is done by early cpufeature code */
return 0;
}
-core_initcall(kaslr_init)
+early_param("nokaslr", parse_nokaslr);