mirror of https://gitee.com/openkylin/linux.git
185 lines
5.4 KiB
C
185 lines
5.4 KiB
C
/*
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* Copyright (C) 2016 Linaro Ltd <ard.biesheuvel@linaro.org>
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*
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* This program is free software; you can redistribute it and/or modify
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* it under the terms of the GNU General Public License version 2 as
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* published by the Free Software Foundation.
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*/
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#include <linux/cache.h>
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#include <linux/crc32.h>
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#include <linux/init.h>
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#include <linux/libfdt.h>
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#include <linux/mm_types.h>
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#include <linux/sched.h>
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#include <linux/types.h>
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#include <asm/fixmap.h>
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#include <asm/kernel-pgtable.h>
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#include <asm/memory.h>
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#include <asm/mmu.h>
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#include <asm/pgtable.h>
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#include <asm/sections.h>
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u64 __ro_after_init module_alloc_base;
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u16 __initdata memstart_offset_seed;
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static __init u64 get_kaslr_seed(void *fdt)
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{
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int node, len;
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fdt64_t *prop;
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u64 ret;
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node = fdt_path_offset(fdt, "/chosen");
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if (node < 0)
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return 0;
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prop = fdt_getprop_w(fdt, node, "kaslr-seed", &len);
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if (!prop || len != sizeof(u64))
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return 0;
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ret = fdt64_to_cpu(*prop);
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*prop = 0;
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return ret;
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}
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static __init const u8 *get_cmdline(void *fdt)
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{
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static __initconst const u8 default_cmdline[] = CONFIG_CMDLINE;
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if (!IS_ENABLED(CONFIG_CMDLINE_FORCE)) {
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int node;
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const u8 *prop;
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node = fdt_path_offset(fdt, "/chosen");
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if (node < 0)
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goto out;
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prop = fdt_getprop(fdt, node, "bootargs", NULL);
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if (!prop)
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goto out;
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return prop;
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}
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out:
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return default_cmdline;
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}
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extern void *__init __fixmap_remap_fdt(phys_addr_t dt_phys, int *size,
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pgprot_t prot);
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/*
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* This routine will be executed with the kernel mapped at its default virtual
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* address, and if it returns successfully, the kernel will be remapped, and
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* start_kernel() will be executed from a randomized virtual offset. The
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* relocation will result in all absolute references (e.g., static variables
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* containing function pointers) to be reinitialized, and zero-initialized
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* .bss variables will be reset to 0.
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*/
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u64 __init kaslr_early_init(u64 dt_phys)
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{
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void *fdt;
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u64 seed, offset, mask, module_range;
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const u8 *cmdline, *str;
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int size;
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/*
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* Set a reasonable default for module_alloc_base in case
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* we end up running with module randomization disabled.
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*/
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module_alloc_base = (u64)_etext - MODULES_VSIZE;
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/*
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* Try to map the FDT early. If this fails, we simply bail,
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* and proceed with KASLR disabled. We will make another
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* attempt at mapping the FDT in setup_machine()
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*/
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early_fixmap_init();
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fdt = __fixmap_remap_fdt(dt_phys, &size, PAGE_KERNEL);
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if (!fdt)
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return 0;
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/*
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* Retrieve (and wipe) the seed from the FDT
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*/
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seed = get_kaslr_seed(fdt);
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if (!seed)
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return 0;
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/*
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* Check if 'nokaslr' appears on the command line, and
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* return 0 if that is the case.
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*/
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cmdline = get_cmdline(fdt);
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str = strstr(cmdline, "nokaslr");
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if (str == cmdline || (str > cmdline && *(str - 1) == ' '))
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return 0;
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/*
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* OK, so we are proceeding with KASLR enabled. Calculate a suitable
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* kernel image offset from the seed. Let's place the kernel in the
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* lower half of the VMALLOC area (VA_BITS - 2).
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* Even if we could randomize at page granularity for 16k and 64k pages,
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* let's always round to 2 MB so we don't interfere with the ability to
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* map using contiguous PTEs
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*/
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mask = ((1UL << (VA_BITS - 2)) - 1) & ~(SZ_2M - 1);
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offset = seed & mask;
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/* use the top 16 bits to randomize the linear region */
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memstart_offset_seed = seed >> 48;
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/*
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* The kernel Image should not extend across a 1GB/32MB/512MB alignment
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* boundary (for 4KB/16KB/64KB granule kernels, respectively). If this
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* happens, round down the KASLR offset by (1 << SWAPPER_TABLE_SHIFT).
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*
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* NOTE: The references to _text and _end below will already take the
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* modulo offset (the physical displacement modulo 2 MB) into
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* account, given that the physical placement is controlled by
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* the loader, and will not change as a result of the virtual
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* mapping we choose.
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*/
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if ((((u64)_text + offset) >> SWAPPER_TABLE_SHIFT) !=
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(((u64)_end + offset) >> SWAPPER_TABLE_SHIFT))
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offset = round_down(offset, 1 << SWAPPER_TABLE_SHIFT);
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if (IS_ENABLED(CONFIG_KASAN))
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/*
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* KASAN does not expect the module region to intersect the
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* vmalloc region, since shadow memory is allocated for each
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* module at load time, whereas the vmalloc region is shadowed
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* by KASAN zero pages. So keep modules out of the vmalloc
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* region if KASAN is enabled.
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*/
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return offset;
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if (IS_ENABLED(CONFIG_RANDOMIZE_MODULE_REGION_FULL)) {
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/*
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* Randomize the module region independently from the core
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* kernel. This prevents modules from leaking any information
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* about the address of the kernel itself, but results in
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* branches between modules and the core kernel that are
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* resolved via PLTs. (Branches between modules will be
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* resolved normally.)
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*/
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module_range = VMALLOC_END - VMALLOC_START - MODULES_VSIZE;
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module_alloc_base = VMALLOC_START;
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} else {
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/*
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* Randomize the module region by setting module_alloc_base to
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* a PAGE_SIZE multiple in the range [_etext - MODULES_VSIZE,
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* _stext) . This guarantees that the resulting region still
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* covers [_stext, _etext], and that all relative branches can
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* be resolved without veneers.
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*/
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module_range = MODULES_VSIZE - (u64)(_etext - _stext);
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module_alloc_base = (u64)_etext + offset - MODULES_VSIZE;
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}
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/* use the lower 21 bits to randomize the base of the module region */
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module_alloc_base += (module_range * (seed & ((1 << 21) - 1))) >> 21;
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module_alloc_base &= PAGE_MASK;
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return offset;
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}
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