linux/arch/x86/mm/kaslr.c

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x86/mm: Implement ASLR for kernel memory regions Randomizes the virtual address space of kernel memory regions for x86_64. This first patch adds the infrastructure and does not randomize any region. The following patches will randomize the physical memory mapping, vmalloc and vmemmap regions. This security feature mitigates exploits relying on predictable kernel addresses. These addresses can be used to disclose the kernel modules base addresses or corrupt specific structures to elevate privileges bypassing the current implementation of KASLR. This feature can be enabled with the CONFIG_RANDOMIZE_MEMORY option. The order of each memory region is not changed. The feature looks at the available space for the regions based on different configuration options and randomizes the base and space between each. The size of the physical memory mapping is the available physical memory. No performance impact was detected while testing the feature. Entropy is generated using the KASLR early boot functions now shared in the lib directory (originally written by Kees Cook). Randomization is done on PGD & PUD page table levels to increase possible addresses. The physical memory mapping code was adapted to support PUD level virtual addresses. This implementation on the best configuration provides 30,000 possible virtual addresses in average for each memory region. An additional low memory page is used to ensure each CPU can start with a PGD aligned virtual address (for realmode). x86/dump_pagetable was updated to correctly display each region. Updated documentation on x86_64 memory layout accordingly. Performance data, after all patches in the series: Kernbench shows almost no difference (-+ less than 1%): Before: Average Optimal load -j 12 Run (std deviation): Elapsed Time 102.63 (1.2695) User Time 1034.89 (1.18115) System Time 87.056 (0.456416) Percent CPU 1092.9 (13.892) Context Switches 199805 (3455.33) Sleeps 97907.8 (900.636) After: Average Optimal load -j 12 Run (std deviation): Elapsed Time 102.489 (1.10636) User Time 1034.86 (1.36053) System Time 87.764 (0.49345) Percent CPU 1095 (12.7715) Context Switches 199036 (4298.1) Sleeps 97681.6 (1031.11) Hackbench shows 0% difference on average (hackbench 90 repeated 10 times): attemp,before,after 1,0.076,0.069 2,0.072,0.069 3,0.066,0.066 4,0.066,0.068 5,0.066,0.067 6,0.066,0.069 7,0.067,0.066 8,0.063,0.067 9,0.067,0.065 10,0.068,0.071 average,0.0677,0.0677 Signed-off-by: Thomas Garnier <thgarnie@google.com> Signed-off-by: Kees Cook <keescook@chromium.org> Cc: Alexander Kuleshov <kuleshovmail@gmail.com> Cc: Alexander Popov <alpopov@ptsecurity.com> Cc: Andrew Morton <akpm@linux-foundation.org> Cc: Andy Lutomirski <luto@kernel.org> Cc: Aneesh Kumar K.V <aneesh.kumar@linux.vnet.ibm.com> Cc: Baoquan He <bhe@redhat.com> Cc: Boris Ostrovsky <boris.ostrovsky@oracle.com> Cc: Borislav Petkov <bp@alien8.de> Cc: Borislav Petkov <bp@suse.de> Cc: Brian Gerst <brgerst@gmail.com> Cc: Christian Borntraeger <borntraeger@de.ibm.com> Cc: Dan Williams <dan.j.williams@intel.com> Cc: Dave Hansen <dave.hansen@linux.intel.com> Cc: Dave Young <dyoung@redhat.com> Cc: Denys Vlasenko <dvlasenk@redhat.com> Cc: Dmitry Vyukov <dvyukov@google.com> Cc: H. Peter Anvin <hpa@zytor.com> Cc: Jan Beulich <JBeulich@suse.com> Cc: Joerg Roedel <jroedel@suse.de> Cc: Jonathan Corbet <corbet@lwn.net> Cc: Josh Poimboeuf <jpoimboe@redhat.com> Cc: Juergen Gross <jgross@suse.com> Cc: Kirill A. Shutemov <kirill.shutemov@linux.intel.com> Cc: Linus Torvalds <torvalds@linux-foundation.org> Cc: Lv Zheng <lv.zheng@intel.com> Cc: Mark Salter <msalter@redhat.com> Cc: Martin Schwidefsky <schwidefsky@de.ibm.com> Cc: Matt Fleming <matt@codeblueprint.co.uk> Cc: Peter Zijlstra <peterz@infradead.org> Cc: Stephen Smalley <sds@tycho.nsa.gov> Cc: Thomas Gleixner <tglx@linutronix.de> Cc: Toshi Kani <toshi.kani@hpe.com> Cc: Xiao Guangrong <guangrong.xiao@linux.intel.com> Cc: Yinghai Lu <yinghai@kernel.org> Cc: kernel-hardening@lists.openwall.com Cc: linux-doc@vger.kernel.org Link: http://lkml.kernel.org/r/1466556426-32664-6-git-send-email-keescook@chromium.org Signed-off-by: Ingo Molnar <mingo@kernel.org>
2016-06-22 08:47:02 +08:00
/*
* This file implements KASLR memory randomization for x86_64. It randomizes
* the virtual address space of kernel memory regions (physical memory
* mapping, vmalloc & vmemmap) for x86_64. This security feature mitigates
* exploits relying on predictable kernel addresses.
*
* Entropy is generated using the KASLR early boot functions now shared in
* the lib directory (originally written by Kees Cook). Randomization is
* done on PGD & PUD page table levels to increase possible addresses. The
* physical memory mapping code was adapted to support PUD level virtual
* addresses. This implementation on the best configuration provides 30,000
* possible virtual addresses in average for each memory region. An additional
* low memory page is used to ensure each CPU can start with a PGD aligned
* virtual address (for realmode).
*
* The order of each memory region is not changed. The feature looks at
* the available space for the regions based on different configuration
* options and randomizes the base and space between each. The size of the
* physical memory mapping is the available physical memory.
*/
#include <linux/kernel.h>
#include <linux/init.h>
#include <linux/random.h>
#include <asm/pgalloc.h>
#include <asm/pgtable.h>
#include <asm/setup.h>
#include <asm/kaslr.h>
#include "mm_internal.h"
#define TB_SHIFT 40
/*
* Virtual address start and end range for randomization. The end changes base
* on configuration to have the highest amount of space for randomization.
* It increases the possible random position for each randomized region.
*
* You need to add an if/def entry if you introduce a new memory region
* compatible with KASLR. Your entry must be in logical order with memory
* layout. For example, ESPFIX is before EFI because its virtual address is
* before. You also need to add a BUILD_BUG_ON in kernel_randomize_memory to
* ensure that this order is correct and won't be changed.
*/
static const unsigned long vaddr_start;
static const unsigned long vaddr_end;
/*
* Memory regions randomized by KASLR (except modules that use a separate logic
* earlier during boot). The list is ordered based on virtual addresses. This
* order is kept after randomization.
*/
static __initdata struct kaslr_memory_region {
unsigned long *base;
unsigned long size_tb;
} kaslr_regions[] = {
};
/* Get size in bytes used by the memory region */
static inline unsigned long get_padding(struct kaslr_memory_region *region)
{
return (region->size_tb << TB_SHIFT);
}
/*
* Apply no randomization if KASLR was disabled at boot or if KASAN
* is enabled. KASAN shadow mappings rely on regions being PGD aligned.
*/
static inline bool kaslr_memory_enabled(void)
{
return kaslr_enabled() && !config_enabled(CONFIG_KASAN);
}
/* Initialize base and padding for each memory region randomized with KASLR */
void __init kernel_randomize_memory(void)
{
size_t i;
unsigned long vaddr = vaddr_start;
unsigned long rand;
struct rnd_state rand_state;
unsigned long remain_entropy;
if (!kaslr_memory_enabled())
return;
/* Calculate entropy available between regions */
remain_entropy = vaddr_end - vaddr_start;
for (i = 0; i < ARRAY_SIZE(kaslr_regions); i++)
remain_entropy -= get_padding(&kaslr_regions[i]);
prandom_seed_state(&rand_state, kaslr_get_random_long("Memory"));
for (i = 0; i < ARRAY_SIZE(kaslr_regions); i++) {
unsigned long entropy;
/*
* Select a random virtual address using the extra entropy
* available.
*/
entropy = remain_entropy / (ARRAY_SIZE(kaslr_regions) - i);
prandom_bytes_state(&rand_state, &rand, sizeof(rand));
entropy = (rand % (entropy + 1)) & PUD_MASK;
vaddr += entropy;
*kaslr_regions[i].base = vaddr;
/*
* Jump the region and add a minimum padding based on
* randomization alignment.
*/
vaddr += get_padding(&kaslr_regions[i]);
vaddr = round_up(vaddr + 1, PUD_SIZE);
remain_entropy -= entropy;
}
}
/*
* Create PGD aligned trampoline table to allow real mode initialization
* of additional CPUs. Consume only 1 low memory page.
*/
void __meminit init_trampoline(void)
{
unsigned long paddr, paddr_next;
pgd_t *pgd;
pud_t *pud_page, *pud_page_tramp;
int i;
if (!kaslr_memory_enabled()) {
init_trampoline_default();
return;
}
pud_page_tramp = alloc_low_page();
paddr = 0;
pgd = pgd_offset_k((unsigned long)__va(paddr));
pud_page = (pud_t *) pgd_page_vaddr(*pgd);
for (i = pud_index(paddr); i < PTRS_PER_PUD; i++, paddr = paddr_next) {
pud_t *pud, *pud_tramp;
unsigned long vaddr = (unsigned long)__va(paddr);
pud_tramp = pud_page_tramp + pud_index(paddr);
pud = pud_page + pud_index(vaddr);
paddr_next = (paddr & PUD_MASK) + PUD_SIZE;
*pud_tramp = *pud;
}
set_pgd(&trampoline_pgd_entry,
__pgd(_KERNPG_TABLE | __pa(pud_page_tramp)));
}