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88107d330d
There are three cases for the trampoline initialization: * 32-bit does nothing * 64-bit with kaslr disabled simply copies a PGD entry from the direct map to the trampoline PGD * 64-bit with kaslr enabled maps the real mode trampoline at PUD level These cases are currently differentiated by a bunch of ifdefs inside asm/include/pgtable.h and the case of 64-bits with kaslr on uses pgd_index() helper. Replacing the ifdefs with a static function in arch/x86/mm/init.c gives clearer code and allows moving pgd_index() to the generic implementation in include/linux/pgtable.h [rppt@linux.ibm.com: take CONFIG_RANDOMIZE_MEMORY into account in kaslr_enabled()] Link: http://lkml.kernel.org/r/20200525104045.GB13212@linux.ibm.com Signed-off-by: Mike Rapoport <rppt@linux.ibm.com> Signed-off-by: Andrew Morton <akpm@linux-foundation.org> Cc: Arnd Bergmann <arnd@arndb.de> Cc: Borislav Petkov <bp@alien8.de> Cc: Brian Cain <bcain@codeaurora.org> Cc: Catalin Marinas <catalin.marinas@arm.com> Cc: Chris Zankel <chris@zankel.net> Cc: "David S. Miller" <davem@davemloft.net> Cc: Geert Uytterhoeven <geert@linux-m68k.org> Cc: Greentime Hu <green.hu@gmail.com> Cc: Greg Ungerer <gerg@linux-m68k.org> Cc: Guan Xuetao <gxt@pku.edu.cn> Cc: Guo Ren <guoren@kernel.org> Cc: Heiko Carstens <heiko.carstens@de.ibm.com> Cc: Helge Deller <deller@gmx.de> Cc: Ingo Molnar <mingo@redhat.com> Cc: Ley Foon Tan <ley.foon.tan@intel.com> Cc: Mark Salter <msalter@redhat.com> Cc: Matthew Wilcox <willy@infradead.org> Cc: Matt Turner <mattst88@gmail.com> Cc: Max Filippov <jcmvbkbc@gmail.com> Cc: Michael Ellerman <mpe@ellerman.id.au> Cc: Michal Simek <monstr@monstr.eu> Cc: Nick Hu <nickhu@andestech.com> Cc: Paul Walmsley <paul.walmsley@sifive.com> Cc: Richard Weinberger <richard@nod.at> Cc: Rich Felker <dalias@libc.org> Cc: Russell King <linux@armlinux.org.uk> Cc: Stafford Horne <shorne@gmail.com> Cc: Thomas Bogendoerfer <tsbogend@alpha.franken.de> Cc: Thomas Gleixner <tglx@linutronix.de> Cc: Tony Luck <tony.luck@intel.com> Cc: Vincent Chen <deanbo422@gmail.com> Cc: Vineet Gupta <vgupta@synopsys.com> Cc: Will Deacon <will@kernel.org> Cc: Yoshinori Sato <ysato@users.sourceforge.jp> Link: http://lkml.kernel.org/r/20200514170327.31389-8-rppt@kernel.org Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
182 lines
5.6 KiB
C
182 lines
5.6 KiB
C
// SPDX-License-Identifier: GPL-2.0
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/*
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* This file implements KASLR memory randomization for x86_64. It randomizes
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* the virtual address space of kernel memory regions (physical memory
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* mapping, vmalloc & vmemmap) for x86_64. This security feature mitigates
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* exploits relying on predictable kernel addresses.
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*
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* Entropy is generated using the KASLR early boot functions now shared in
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* the lib directory (originally written by Kees Cook). Randomization is
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* done on PGD & P4D/PUD page table levels to increase possible addresses.
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* The physical memory mapping code was adapted to support P4D/PUD level
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* virtual addresses. This implementation on the best configuration provides
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* 30,000 possible virtual addresses in average for each memory region.
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* An additional low memory page is used to ensure each CPU can start with
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* a PGD aligned virtual address (for realmode).
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*
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* The order of each memory region is not changed. The feature looks at
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* the available space for the regions based on different configuration
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* options and randomizes the base and space between each. The size of the
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* physical memory mapping is the available physical memory.
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*/
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#include <linux/kernel.h>
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#include <linux/init.h>
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#include <linux/random.h>
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#include <linux/memblock.h>
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#include <linux/pgtable.h>
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#include <asm/pgalloc.h>
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#include <asm/setup.h>
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#include <asm/kaslr.h>
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#include "mm_internal.h"
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#define TB_SHIFT 40
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/*
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* The end address could depend on more configuration options to make the
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* highest amount of space for randomization available, but that's too hard
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* to keep straight and caused issues already.
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*/
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static const unsigned long vaddr_end = CPU_ENTRY_AREA_BASE;
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/*
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* Memory regions randomized by KASLR (except modules that use a separate logic
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* earlier during boot). The list is ordered based on virtual addresses. This
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* order is kept after randomization.
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*/
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static __initdata struct kaslr_memory_region {
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unsigned long *base;
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unsigned long size_tb;
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} kaslr_regions[] = {
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{ &page_offset_base, 0 },
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{ &vmalloc_base, 0 },
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{ &vmemmap_base, 0 },
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};
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/* Get size in bytes used by the memory region */
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static inline unsigned long get_padding(struct kaslr_memory_region *region)
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{
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return (region->size_tb << TB_SHIFT);
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}
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/* Initialize base and padding for each memory region randomized with KASLR */
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void __init kernel_randomize_memory(void)
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{
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size_t i;
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unsigned long vaddr_start, vaddr;
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unsigned long rand, memory_tb;
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struct rnd_state rand_state;
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unsigned long remain_entropy;
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unsigned long vmemmap_size;
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vaddr_start = pgtable_l5_enabled() ? __PAGE_OFFSET_BASE_L5 : __PAGE_OFFSET_BASE_L4;
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vaddr = vaddr_start;
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/*
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* These BUILD_BUG_ON checks ensure the memory layout is consistent
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* with the vaddr_start/vaddr_end variables. These checks are very
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* limited....
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*/
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BUILD_BUG_ON(vaddr_start >= vaddr_end);
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BUILD_BUG_ON(vaddr_end != CPU_ENTRY_AREA_BASE);
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BUILD_BUG_ON(vaddr_end > __START_KERNEL_map);
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if (!kaslr_memory_enabled())
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return;
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kaslr_regions[0].size_tb = 1 << (MAX_PHYSMEM_BITS - TB_SHIFT);
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kaslr_regions[1].size_tb = VMALLOC_SIZE_TB;
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/*
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* Update Physical memory mapping to available and
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* add padding if needed (especially for memory hotplug support).
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*/
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BUG_ON(kaslr_regions[0].base != &page_offset_base);
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memory_tb = DIV_ROUND_UP(max_pfn << PAGE_SHIFT, 1UL << TB_SHIFT) +
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CONFIG_RANDOMIZE_MEMORY_PHYSICAL_PADDING;
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/* Adapt phyiscal memory region size based on available memory */
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if (memory_tb < kaslr_regions[0].size_tb)
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kaslr_regions[0].size_tb = memory_tb;
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/*
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* Calculate the vmemmap region size in TBs, aligned to a TB
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* boundary.
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*/
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vmemmap_size = (kaslr_regions[0].size_tb << (TB_SHIFT - PAGE_SHIFT)) *
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sizeof(struct page);
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kaslr_regions[2].size_tb = DIV_ROUND_UP(vmemmap_size, 1UL << TB_SHIFT);
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/* Calculate entropy available between regions */
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remain_entropy = vaddr_end - vaddr_start;
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for (i = 0; i < ARRAY_SIZE(kaslr_regions); i++)
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remain_entropy -= get_padding(&kaslr_regions[i]);
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prandom_seed_state(&rand_state, kaslr_get_random_long("Memory"));
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for (i = 0; i < ARRAY_SIZE(kaslr_regions); i++) {
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unsigned long entropy;
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/*
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* Select a random virtual address using the extra entropy
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* available.
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*/
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entropy = remain_entropy / (ARRAY_SIZE(kaslr_regions) - i);
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prandom_bytes_state(&rand_state, &rand, sizeof(rand));
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entropy = (rand % (entropy + 1)) & PUD_MASK;
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vaddr += entropy;
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*kaslr_regions[i].base = vaddr;
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/*
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* Jump the region and add a minimum padding based on
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* randomization alignment.
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*/
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vaddr += get_padding(&kaslr_regions[i]);
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vaddr = round_up(vaddr + 1, PUD_SIZE);
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remain_entropy -= entropy;
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}
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}
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void __meminit init_trampoline_kaslr(void)
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{
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pud_t *pud_page_tramp, *pud, *pud_tramp;
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p4d_t *p4d_page_tramp, *p4d, *p4d_tramp;
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unsigned long paddr, vaddr;
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pgd_t *pgd;
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pud_page_tramp = alloc_low_page();
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/*
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* There are two mappings for the low 1MB area, the direct mapping
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* and the 1:1 mapping for the real mode trampoline:
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*
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* Direct mapping: virt_addr = phys_addr + PAGE_OFFSET
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* 1:1 mapping: virt_addr = phys_addr
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*/
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paddr = 0;
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vaddr = (unsigned long)__va(paddr);
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pgd = pgd_offset_k(vaddr);
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p4d = p4d_offset(pgd, vaddr);
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pud = pud_offset(p4d, vaddr);
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pud_tramp = pud_page_tramp + pud_index(paddr);
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*pud_tramp = *pud;
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if (pgtable_l5_enabled()) {
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p4d_page_tramp = alloc_low_page();
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p4d_tramp = p4d_page_tramp + p4d_index(paddr);
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set_p4d(p4d_tramp,
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__p4d(_KERNPG_TABLE | __pa(pud_page_tramp)));
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set_pgd(&trampoline_pgd_entry,
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__pgd(_KERNPG_TABLE | __pa(p4d_page_tramp)));
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} else {
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set_pgd(&trampoline_pgd_entry,
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__pgd(_KERNPG_TABLE | __pa(pud_page_tramp)));
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}
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}
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