// SPDX-License-Identifier: GPL-2.0-only
/*
 * Copyright (C) 2016 Linaro Ltd <ard.biesheuvel@linaro.org>
 */

#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 <asm/cacheflush.h>
#include <asm/fixmap.h>
#include <asm/kernel-pgtable.h>
#include <asm/memory.h>
#include <asm/mmu.h>
#include <asm/sections.h>
#include <asm/setup.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;
}

struct arm64_ftr_override kaslr_feature_override __initdata;

/*
 * 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(void)
{
        void *fdt;
        u64 seed, offset, mask, module_range;
        unsigned long raw;

        /*
         * 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;
        dcache_clean_inval_poc((unsigned long)&module_alloc_base,
                            (unsigned long)&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()
         */
        fdt = get_early_fdt_ptr();
        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.
         */
        if (kaslr_feature_override.val & kaslr_feature_override.mask & 0xf) {
                kaslr_status = KASLR_DISABLED_CMDLINE;
                return 0;
        }

        /*
         * Mix in any entropy obtainable architecturally if enabled
         * and supported.
         */

        if (arch_get_random_seed_long_early(&raw))
                seed ^= raw;

        if (!seed) {
                kaslr_status = KASLR_DISABLED_NO_SEED;
                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
         * 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
         */
        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_VMALLOC) &&
            (IS_ENABLED(CONFIG_KASAN_GENERIC) ||
             IS_ENABLED(CONFIG_KASAN_SW_TAGS)))
                /*
                 * 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 is shadowed by KASAN zero pages. So keep modules
                 * out of the vmalloc region if KASAN is enabled without
                 * KASAN_VMALLOC, 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 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;

        dcache_clean_inval_poc((unsigned long)&module_alloc_base,
                            (unsigned long)&module_alloc_base +
                                    sizeof(module_alloc_base));
        dcache_clean_inval_poc((unsigned long)&memstart_offset_seed,
                            (unsigned long)&memstart_offset_seed +
                                    sizeof(memstart_offset_seed));

        return offset;
}

static int __init kaslr_init(void)
{
        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;
        }

        return 0;
}
core_initcall(kaslr_init)