// SPDX-License-Identifier: GPL-2.0
/*
* KMSAN initialization routines.
*
* Copyright (C) 2017-2021 Google LLC
* Author: Alexander Potapenko <[email protected]>
*
*/
#include "kmsan.h"
#include <asm/sections.h>
#include <linux/mm.h>
#include <linux/memblock.h>
#include "../internal.h"
#define NUM_FUTURE_RANGES 128
struct start_end_pair {
u64 start, end;
};
static struct start_end_pair start_end_pairs[NUM_FUTURE_RANGES] __initdata;
static int future_index __initdata;
/*
* Record a range of memory for which the metadata pages will be created once
* the page allocator becomes available.
*/
static void __init kmsan_record_future_shadow_range(void *start, void *end)
{
u64 nstart = (u64)start, nend = (u64)end, cstart, cend;
bool merged = false;
KMSAN_WARN_ON(future_index == NUM_FUTURE_RANGES);
KMSAN_WARN_ON((nstart >= nend) ||
/* Virtual address 0 is valid on s390. */
(!IS_ENABLED(CONFIG_S390) && !nstart) ||
!nend);
nstart = ALIGN_DOWN(nstart, PAGE_SIZE);
nend = ALIGN(nend, PAGE_SIZE);
/*
* Scan the existing ranges to see if any of them overlaps with
* [start, end). In that case, merge the two ranges instead of
* creating a new one.
* The number of ranges is less than 20, so there is no need to organize
* them into a more intelligent data structure.
*/
for (int i = 0; i < future_index; i++) {
cstart = start_end_pairs[i].start;
cend = start_end_pairs[i].end;
if ((cstart < nstart && cend < nstart) ||
(cstart > nend && cend > nend))
/* ranges are disjoint - do not merge */
continue;
start_end_pairs[i].start = min(nstart, cstart);
start_end_pairs[i].end = max(nend, cend);
merged = true;
break;
}
if (merged)
return;
start_end_pairs[future_index].start = nstart;
start_end_pairs[future_index].end = nend;
future_index++;
}
/*
* Initialize the shadow for existing mappings during kernel initialization.
* These include kernel text/data sections, NODE_DATA and future ranges
* registered while creating other data (e.g. percpu).
*
* Allocations via memblock can be only done before slab is initialized.
*/
void __init kmsan_init_shadow(void)
{
const size_t nd_size = sizeof(pg_data_t);
phys_addr_t p_start, p_end;
u64 loop;
int nid;
for_each_reserved_mem_range(loop, &p_start, &p_end)
kmsan_record_future_shadow_range(phys_to_virt(p_start),
phys_to_virt(p_end));
/* Allocate shadow for .data */
kmsan_record_future_shadow_range(_sdata, _edata);
for_each_online_node(nid)
kmsan_record_future_shadow_range(
NODE_DATA(nid), (char *)NODE_DATA(nid) + nd_size);
for (int i = 0; i < future_index; i++)
kmsan_init_alloc_meta_for_range(
(void *)start_end_pairs[i].start,
(void *)start_end_pairs[i].end);
}
struct metadata_page_pair {
struct page *shadow, *origin;
};
static struct metadata_page_pair held_back[NR_PAGE_ORDERS] __initdata;
/*
* 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.
* We store the pointers to the returned blocks of pages in held_back[] grouped
* by their order: when kmsan_memblock_free_pages() is called for the first
* time with a certain order, it is reserved as a shadow block, for the second
* time - as an origin block. On the third time the incoming block receives its
* shadow and origin ranges from the previously saved shadow and origin blocks,
* after which held_back[order] can be used again.
*
* At the very end there may be leftover blocks in held_back[]. They are
* collected later by kmsan_memblock_discard().
*/
bool kmsan_memblock_free_pages(struct page *page, unsigned int order)
{
struct page *shadow, *origin;
if (!held_back[order].shadow) {
held_back[order].shadow = page;
return false;
}
if (!held_back[order].origin) {
held_back[order].origin = page;
return false;
}
shadow = held_back[order].shadow;
origin = held_back[order].origin;
kmsan_setup_meta(page, shadow, origin, order);
held_back[order].shadow = NULL;
held_back[order].origin = NULL;
return true;
}
#define MAX_BLOCKS 8
struct smallstack {
struct page *items[MAX_BLOCKS];
int index;
int order;
};
static struct smallstack collect = {
.index = 0,
.order = MAX_PAGE_ORDER,
};
static void smallstack_push(struct smallstack *stack, struct page *pages)
{
KMSAN_WARN_ON(stack->index == MAX_BLOCKS);
stack->items[stack->index] = pages;
stack->index++;
}
#undef MAX_BLOCKS
static struct page *smallstack_pop(struct smallstack *stack)
{
struct page *ret;
KMSAN_WARN_ON(stack->index == 0);
stack->index--;
ret = stack->items[stack->index];
stack->items[stack->index] = NULL;
return ret;
}
static void do_collection(void)
{
struct page *page, *shadow, *origin;
while (collect.index >= 3) {
page = smallstack_pop(&collect);
shadow = smallstack_pop(&collect);
origin = smallstack_pop(&collect);
kmsan_setup_meta(page, shadow, origin, collect.order);
__free_pages_core(page, collect.order, MEMINIT_EARLY);
}
}
static void collect_split(void)
{
struct smallstack tmp = {
.order = collect.order - 1,
.index = 0,
};
struct page *page;
if (!collect.order)
return;
while (collect.index) {
page = smallstack_pop(&collect);
smallstack_push(&tmp, &page[0]);
smallstack_push(&tmp, &page[1 << tmp.order]);
}
__memcpy(&collect, &tmp, sizeof(tmp));
}
/*
* Memblock is about to go away. Split the page blocks left over in held_back[]
* and return 1/3 of that memory to the system.
*/
static void kmsan_memblock_discard(void)
{
/*
* For each order=N:
* - push held_back[N].shadow and .origin to @collect;
* - while there are >= 3 elements in @collect, do garbage collection:
* - pop 3 ranges from @collect;
* - use two of them as shadow and origin for the third one;
* - repeat;
* - split each remaining element from @collect into 2 ranges of
* order=N-1,
* - repeat.
*/
collect.order = MAX_PAGE_ORDER;
for (int i = MAX_PAGE_ORDER; i >= 0; i--) {
if (held_back[i].shadow)
smallstack_push(&collect, held_back[i].shadow);
if (held_back[i].origin)
smallstack_push(&collect, held_back[i].origin);
held_back[i].shadow = NULL;
held_back[i].origin = NULL;
do_collection();
collect_split();
}
}
void __init kmsan_init_runtime(void)
{
/* Assuming current is init_task */
kmsan_internal_task_create(current);
kmsan_memblock_discard();
pr_info("Starting KernelMemorySanitizer\n");
pr_info("ATTENTION: KMSAN is a debugging tool! Do not use it on production machines!\n");
kmsan_enabled = true;
}
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