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kmsan_shadow.c
381 lines (331 loc) · 10.4 KB
/
kmsan_shadow.c
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// SPDX-License-Identifier: GPL-2.0
/*
* KMSAN shadow implementation.
*
* Copyright (C) 2017-2019 Google LLC
* Author: Alexander Potapenko <glider@google.com>
*
* This program is free software; you can redistribute it and/or modify
* it under the terms of the GNU General Public License version 2 as
* published by the Free Software Foundation.
*
*/
#include <asm/cpu_entry_area.h>
#include <asm/page.h>
#include <asm/pgtable_64_types.h>
#include <asm/tlbflush.h>
#include <linux/memblock.h>
#include <linux/mm_types.h>
#include <linux/percpu-defs.h>
#include <linux/slab.h>
#include <linux/smp.h>
#include <linux/stddef.h>
#include "kmsan.h"
#include "kmsan_shadow.h"
#define shadow_page_for(page) ((page)->shadow)
#define origin_page_for(page) ((page)->origin)
#define shadow_ptr_for(page) (page_address((page)->shadow))
#define origin_ptr_for(page) (page_address((page)->origin))
#define has_shadow_page(page) (!!((page)->shadow))
#define has_origin_page(page) (!!((page)->origin))
#define set_no_shadow_origin_page(page) \
do { \
(page)->shadow = NULL; \
(page)->origin = NULL; \
} while (0) /**/
DEFINE_PER_CPU(char[CPU_ENTRY_AREA_SIZE], cpu_entry_area_shadow);
DEFINE_PER_CPU(char[CPU_ENTRY_AREA_SIZE], cpu_entry_area_origin);
/*
* Dummy load and store pages to be used when the real metadata is unavailable.
* There are separate pages for loads and stores, so that every load returns a
* zero, and every store doesn't affect other loads.
*/
char dummy_load_page[PAGE_SIZE] __aligned(PAGE_SIZE);
char dummy_store_page[PAGE_SIZE] __aligned(PAGE_SIZE);
/*
* Taken from arch/x86/mm/physaddr.h to avoid using an instrumented version.
*/
static int kmsan_phys_addr_valid(unsigned long addr)
{
#ifdef CONFIG_PHYS_ADDR_T_64BIT
return !(addr >> boot_cpu_data.x86_phys_bits);
#else
return 1;
#endif
}
/*
* Taken from arch/x86/mm/physaddr.c to avoid using an instrumented version.
*/
static bool kmsan_virt_addr_valid(void *addr)
{
unsigned long x = (unsigned long)addr;
unsigned long y = x - __START_KERNEL_map;
/* use the carry flag to determine if x was < __START_KERNEL_map */
if (unlikely(x > y)) {
x = y + phys_base;
if (y >= KERNEL_IMAGE_SIZE)
return false;
} else {
x = y + (__START_KERNEL_map - PAGE_OFFSET);
/* carry flag will be set if starting x was >= PAGE_OFFSET */
if ((x > y) || !kmsan_phys_addr_valid(x))
return false;
}
return pfn_valid(x >> PAGE_SHIFT);
}
static unsigned long vmalloc_meta(void *addr, bool is_origin)
{
unsigned long addr64 = (unsigned long)addr, off;
BUG_ON(is_origin && !IS_ALIGNED(addr64, ORIGIN_SIZE));
if (kmsan_internal_is_vmalloc_addr(addr))
return addr64 + (is_origin ? KMSAN_VMALLOC_ORIGIN_OFFSET
: KMSAN_VMALLOC_SHADOW_OFFSET);
if (kmsan_internal_is_module_addr(addr)) {
off = addr64 - MODULES_VADDR;
return off + (is_origin ? KMSAN_MODULES_ORIGIN_START
: KMSAN_MODULES_SHADOW_START);
}
return 0;
}
static void *get_cea_meta_or_null(void *addr, bool is_origin)
{
int cpu = smp_processor_id();
int off;
char *metadata_array;
if (((u64)addr < CPU_ENTRY_AREA_BASE) ||
((u64)addr >= (CPU_ENTRY_AREA_BASE + CPU_ENTRY_AREA_MAP_SIZE)))
return NULL;
off = (char *)addr - (char *)get_cpu_entry_area(cpu);
if ((off < 0) || (off >= CPU_ENTRY_AREA_SIZE))
return NULL;
metadata_array = is_origin ? cpu_entry_area_origin :
cpu_entry_area_shadow;
return &per_cpu(metadata_array[off], cpu);
}
static struct page *virt_to_page_or_null(void *vaddr)
{
if (kmsan_virt_addr_valid(vaddr))
return virt_to_page(vaddr);
else
return NULL;
}
struct shadow_origin_ptr kmsan_get_shadow_origin_ptr(void *address, u64 size,
bool store)
{
struct shadow_origin_ptr ret;
void *shadow;
if (size > PAGE_SIZE)
panic("size too big in %s(%px, %d, %d)\n",
__func__, address, size, store);
if (!kmsan_ready || kmsan_in_runtime())
goto return_dummy;
BUG_ON(!metadata_is_contiguous(address, size, META_SHADOW));
shadow = kmsan_get_metadata(address, size, META_SHADOW);
if (!shadow)
goto return_dummy;
ret.s = shadow;
ret.o = kmsan_get_metadata(address, size, META_ORIGIN);
return ret;
return_dummy:
if (store) {
ret.s = dummy_store_page;
ret.o = dummy_store_page;
} else {
ret.s = dummy_load_page;
ret.o = dummy_load_page;
}
return ret;
}
/*
* Obtain the shadow or origin pointer for the given address, or NULL if there's
* none. The caller must check the return value for being non-NULL if needed.
* The return value of this function should not depend on whether we're in the
* runtime or not.
*/
void *kmsan_get_metadata(void *address, size_t size, bool is_origin)
{
struct page *page;
void *ret;
u64 addr = (u64)address, pad, off;
if (is_origin && !IS_ALIGNED(addr, ORIGIN_SIZE)) {
pad = addr % ORIGIN_SIZE;
addr -= pad;
size += pad;
}
address = (void *)addr;
if (kmsan_internal_is_vmalloc_addr(address) ||
kmsan_internal_is_module_addr(address))
return (void *)vmalloc_meta(address, is_origin);
ret = get_cea_meta_or_null(address, is_origin);
if (ret)
return ret;
page = virt_to_page_or_null(address);
if (!page)
return NULL;
if (!has_shadow_page(page) || !has_origin_page(page))
return NULL;
off = addr % PAGE_SIZE;
ret = (is_origin ? origin_ptr_for(page) : shadow_ptr_for(page)) + off;
return ret;
}
/* Allocate metadata for pages allocated at boot time. */
void __init kmsan_init_alloc_meta_for_range(void *start, void *end)
{
u64 addr, size;
struct page *page;
void *shadow, *origin;
struct page *shadow_p, *origin_p;
start = (void *)ALIGN_DOWN((u64)start, PAGE_SIZE);
size = ALIGN((u64)end - (u64)start, PAGE_SIZE);
shadow = memblock_alloc(size, PAGE_SIZE);
origin = memblock_alloc(size, PAGE_SIZE);
for (addr = 0; addr < size; addr += PAGE_SIZE) {
page = virt_to_page_or_null((char *)start + addr);
shadow_p = virt_to_page_or_null((char *)shadow + addr);
set_no_shadow_origin_page(shadow_p);
shadow_page_for(page) = shadow_p;
origin_p = virt_to_page_or_null((char *)origin + addr);
set_no_shadow_origin_page(origin_p);
origin_page_for(page) = origin_p;
}
}
/* Called from mm/memory.c */
void kmsan_copy_page_meta(struct page *dst, struct page *src)
{
unsigned long irq_flags;
if (!kmsan_ready || kmsan_in_runtime())
return;
if (!has_shadow_page(src)) {
kmsan_internal_unpoison_shadow(page_address(dst), PAGE_SIZE,
/*checked*/false);
return;
}
if (!has_shadow_page(dst))
return;
irq_flags = kmsan_enter_runtime();
__memcpy(shadow_ptr_for(dst), shadow_ptr_for(src),
PAGE_SIZE);
BUG_ON(!has_origin_page(src) || !has_origin_page(dst));
__memcpy(origin_ptr_for(dst), origin_ptr_for(src),
PAGE_SIZE);
kmsan_leave_runtime(irq_flags);
}
EXPORT_SYMBOL(kmsan_copy_page_meta);
/*
* Helper function to allocate page metadata.
* TODO(glider): merge into kmsan_alloc_page().
* */
static int kmsan_internal_alloc_meta_for_pages(struct page *page,
unsigned int order,
gfp_t flags, int node)
{
struct page *shadow = shadow_page_for(page), *origin = origin_page_for(page);
int pages = 1 << order;
int i;
bool initialized = (flags & __GFP_ZERO) || !kmsan_ready;
depot_stack_handle_t handle;
if (!initialized) {
__memset(page_address(shadow), -1, PAGE_SIZE * pages);
handle = kmsan_save_stack_with_flags(flags, /*extra_bits*/0);
/*
* Addresses are page-aligned, pages are contiguous, so it's ok
* to just fill the origin pages with |handle|.
*/
for (i = 0; i < PAGE_SIZE * pages / sizeof(handle); i++)
((depot_stack_handle_t *)page_address(origin))[i] =
handle;
} else {
__memset(page_address(shadow), 0, PAGE_SIZE * pages);
__memset(page_address(origin), 0, PAGE_SIZE * pages);
}
return 0;
}
/* Called from mm/page_alloc.c */
int kmsan_alloc_page(struct page *page, unsigned int order, gfp_t flags)
{
unsigned long irq_flags;
int ret;
if (kmsan_in_runtime())
return 0;
irq_flags = kmsan_enter_runtime();
ret = kmsan_internal_alloc_meta_for_pages(page, order, flags, -1);
kmsan_leave_runtime(irq_flags);
return ret;
}
/* Called from mm/page_alloc.c */
void kmsan_free_page(struct page *page, unsigned int order)
{
return; // really nothing to do here. Could rewrite shadow instead.
}
EXPORT_SYMBOL(kmsan_free_page);
/* Called from mm/vmalloc.c */
void kmsan_vmap_page_range_noflush(unsigned long start, unsigned long end,
pgprot_t prot, struct page **pages)
{
int nr, i, mapped;
struct page **s_pages, **o_pages;
unsigned long shadow_start, shadow_end, origin_start, origin_end;
if (!kmsan_ready || kmsan_in_runtime())
return;
shadow_start = vmalloc_meta((void *)start, META_SHADOW);
if (!shadow_start)
return;
BUG_ON(start >= end);
nr = (end - start) / PAGE_SIZE;
s_pages = kcalloc(nr, sizeof(struct page *), GFP_KERNEL);
o_pages = kcalloc(nr, sizeof(struct page *), GFP_KERNEL);
if (!s_pages || !o_pages)
goto ret;
for (i = 0; i < nr; i++) {
s_pages[i] = shadow_page_for(pages[i]);
o_pages[i] = origin_page_for(pages[i]);
}
prot = __pgprot(pgprot_val(prot) | _PAGE_NX);
prot = PAGE_KERNEL;
shadow_end = vmalloc_meta((void *)end, META_SHADOW);
origin_start = vmalloc_meta((void *)start, META_ORIGIN);
origin_end = vmalloc_meta((void *)end, META_ORIGIN);
mapped = __vmap_page_range_noflush(shadow_start, shadow_end,
prot, s_pages);
BUG_ON(mapped != nr);
flush_tlb_kernel_range(shadow_start, shadow_end);
mapped = __vmap_page_range_noflush(origin_start, origin_end,
prot, o_pages);
BUG_ON(mapped != nr);
flush_tlb_kernel_range(origin_start, origin_end);
ret:
kfree(s_pages);
kfree(o_pages);
}
struct page *saved_shadow = NULL, *saved_origin = NULL;
/*
* Eager metadata allocation. When the memblock allocator is freeing pages to
* pagealloc, we use 2/3 of them as metadata for the remaining 1/3.
* Most of the time memblock_free_pages() is called with order=10, see
* __free_pages_memory(). Therefore right now we just leak pages with different
* order (their total number is about 3*1024).
*/
bool kmsan_memblock_free_pages(struct page *page, unsigned int order)
{
int i, pages = 1 << order;
if (order != 10)
/* Leaking these pages. */
return false;
if (!saved_shadow) {
saved_shadow = page;
return false;
}
if (!saved_origin) {
saved_origin = page;
return false;
}
for (i = 0; i < pages; i++) {
set_no_shadow_origin_page(&saved_shadow[i]);
set_no_shadow_origin_page(&saved_origin[i]);
shadow_page_for(&page[i]) = &saved_shadow[i];
origin_page_for(&page[i]) = &saved_origin[i];
}
saved_shadow = NULL;
saved_origin = NULL;
return true;
}