// SPDX-License-Identifier: GPL-2.0
/*
* KMSAN runtime library.
*
* Copyright (C) 2017-2022 Google LLC
* Author: Alexander Potapenko <[email protected]>
*
*/
#include <asm/page.h>
#include <linux/compiler.h>
#include <linux/export.h>
#include <linux/highmem.h>
#include <linux/interrupt.h>
#include <linux/kernel.h>
#include <linux/kmsan_types.h>
#include <linux/memory.h>
#include <linux/mm.h>
#include <linux/mm_types.h>
#include <linux/mmzone.h>
#include <linux/percpu-defs.h>
#include <linux/preempt.h>
#include <linux/slab.h>
#include <linux/stackdepot.h>
#include <linux/stacktrace.h>
#include <linux/types.h>
#include <linux/vmalloc.h>
#include "../slab.h"
#include "kmsan.h"
bool kmsan_enabled __read_mostly;
/*
* Per-CPU KMSAN context to be used in interrupts, where current->kmsan is
* unavaliable.
*/
DEFINE_PER_CPU(struct kmsan_ctx, kmsan_percpu_ctx);
void kmsan_internal_task_create(struct task_struct *task)
{
struct kmsan_ctx *ctx = &task->kmsan_ctx;
struct thread_info *info = current_thread_info();
__memset(ctx, 0, sizeof(*ctx));
kmsan_internal_unpoison_memory(info, sizeof(*info), false);
}
void kmsan_internal_poison_memory(void *address, size_t size, gfp_t flags,
unsigned int poison_flags)
{
u32 extra_bits =
kmsan_extra_bits(/*depth*/ 0, poison_flags & KMSAN_POISON_FREE);
bool checked = poison_flags & KMSAN_POISON_CHECK;
depot_stack_handle_t handle;
handle = kmsan_save_stack_with_flags(flags, extra_bits);
kmsan_internal_set_shadow_origin(address, size, -1, handle, checked);
}
void kmsan_internal_unpoison_memory(void *address, size_t size, bool checked)
{
kmsan_internal_set_shadow_origin(address, size, 0, 0, checked);
}
depot_stack_handle_t kmsan_save_stack_with_flags(gfp_t flags,
unsigned int extra)
{
unsigned long entries[KMSAN_STACK_DEPTH];
unsigned int nr_entries;
depot_stack_handle_t handle;
nr_entries = stack_trace_save(entries, KMSAN_STACK_DEPTH, 0);
/* Don't sleep. */
flags &= ~(__GFP_DIRECT_RECLAIM | __GFP_KSWAPD_RECLAIM);
handle = stack_depot_save(entries, nr_entries, flags);
return stack_depot_set_extra_bits(handle, extra);
}
/* Copy the metadata following the memmove() behavior. */
void kmsan_internal_memmove_metadata(void *dst, void *src, size_t n)
{
depot_stack_handle_t prev_old_origin = 0, prev_new_origin = 0;
int i, iter, step, src_off, dst_off, oiter_src, oiter_dst;
depot_stack_handle_t old_origin = 0, new_origin = 0;
depot_stack_handle_t *origin_src, *origin_dst;
u8 *shadow_src, *shadow_dst;
u32 *align_shadow_dst;
bool backwards;
shadow_dst = kmsan_get_metadata(dst, KMSAN_META_SHADOW);
if (!shadow_dst)
return;
KMSAN_WARN_ON(!kmsan_metadata_is_contiguous(dst, n));
align_shadow_dst =
(u32 *)ALIGN_DOWN((u64)shadow_dst, KMSAN_ORIGIN_SIZE);
shadow_src = kmsan_get_metadata(src, KMSAN_META_SHADOW);
if (!shadow_src) {
/* @src is untracked: mark @dst as initialized. */
kmsan_internal_unpoison_memory(dst, n, /*checked*/ false);
return;
}
KMSAN_WARN_ON(!kmsan_metadata_is_contiguous(src, n));
origin_dst = kmsan_get_metadata(dst, KMSAN_META_ORIGIN);
origin_src = kmsan_get_metadata(src, KMSAN_META_ORIGIN);
KMSAN_WARN_ON(!origin_dst || !origin_src);
backwards = dst > src;
step = backwards ? -1 : 1;
iter = backwards ? n - 1 : 0;
src_off = (u64)src % KMSAN_ORIGIN_SIZE;
dst_off = (u64)dst % KMSAN_ORIGIN_SIZE;
/* Copy shadow bytes one by one, updating the origins if necessary. */
for (i = 0; i < n; i++, iter += step) {
oiter_src = (iter + src_off) / KMSAN_ORIGIN_SIZE;
oiter_dst = (iter + dst_off) / KMSAN_ORIGIN_SIZE;
if (!shadow_src[iter]) {
shadow_dst[iter] = 0;
if (!align_shadow_dst[oiter_dst])
origin_dst[oiter_dst] = 0;
continue;
}
shadow_dst[iter] = shadow_src[iter];
old_origin = origin_src[oiter_src];
if (old_origin == prev_old_origin)
new_origin = prev_new_origin;
else {
/*
* kmsan_internal_chain_origin() may return
* NULL, but we don't want to lose the previous
* origin value.
*/
new_origin = kmsan_internal_chain_origin(old_origin);
if (!new_origin)
new_origin = old_origin;
}
origin_dst[oiter_dst] = new_origin;
prev_new_origin = new_origin;
prev_old_origin = old_origin;
}
}
depot_stack_handle_t kmsan_internal_chain_origin(depot_stack_handle_t id)
{
unsigned long entries[3];
u32 extra_bits;
int depth;
bool uaf;
depot_stack_handle_t handle;
if (!id)
return id;
/*
* Make sure we have enough spare bits in @id to hold the UAF bit and
* the chain depth.
*/
BUILD_BUG_ON(
(1 << STACK_DEPOT_EXTRA_BITS) <= (KMSAN_MAX_ORIGIN_DEPTH << 1));
extra_bits = stack_depot_get_extra_bits(id);
depth = kmsan_depth_from_eb(extra_bits);
uaf = kmsan_uaf_from_eb(extra_bits);
/*
* Stop chaining origins once the depth reached KMSAN_MAX_ORIGIN_DEPTH.
* This mostly happens in the case structures with uninitialized padding
* are copied around many times. Origin chains for such structures are
* usually periodic, and it does not make sense to fully store them.
*/
if (depth == KMSAN_MAX_ORIGIN_DEPTH)
return id;
depth++;
extra_bits = kmsan_extra_bits(depth, uaf);
entries[0] = KMSAN_CHAIN_MAGIC_ORIGIN;
entries[1] = kmsan_save_stack_with_flags(__GFP_HIGH, 0);
entries[2] = id;
/*
* @entries is a local var in non-instrumented code, so KMSAN does not
* know it is initialized. Explicitly unpoison it to avoid false
* positives when stack_depot_save() passes it to instrumented code.
*/
kmsan_internal_unpoison_memory(entries, sizeof(entries), false);
handle = stack_depot_save(entries, ARRAY_SIZE(entries), __GFP_HIGH);
return stack_depot_set_extra_bits(handle, extra_bits);
}
void kmsan_internal_set_shadow_origin(void *addr, size_t size, int b,
u32 origin, bool checked)
{
u64 address = (u64)addr;
u32 *shadow_start, *origin_start;
size_t pad = 0;
KMSAN_WARN_ON(!kmsan_metadata_is_contiguous(addr, size));
shadow_start = kmsan_get_metadata(addr, KMSAN_META_SHADOW);
if (!shadow_start) {
/*
* kmsan_metadata_is_contiguous() is true, so either all shadow
* and origin pages are NULL, or all are non-NULL.
*/
if (checked) {
pr_err("%s: not memsetting %ld bytes starting at %px, because the shadow is NULL\n",
__func__, size, addr);
KMSAN_WARN_ON(true);
}
return;
}
__memset(shadow_start, b, size);
if (!IS_ALIGNED(address, KMSAN_ORIGIN_SIZE)) {
pad = address % KMSAN_ORIGIN_SIZE;
address -= pad;
size += pad;
}
size = ALIGN(size, KMSAN_ORIGIN_SIZE);
origin_start =
(u32 *)kmsan_get_metadata((void *)address, KMSAN_META_ORIGIN);
/*
* If the new origin is non-zero, assume that the shadow byte is also non-zero,
* and unconditionally overwrite the old origin slot.
* If the new origin is zero, overwrite the old origin slot iff the
* corresponding shadow slot is zero.
*/
for (int i = 0; i < size / KMSAN_ORIGIN_SIZE; i++) {
if (origin || !shadow_start[i])
origin_start[i] = origin;
}
}
struct page *kmsan_vmalloc_to_page_or_null(void *vaddr)
{
struct page *page;
if (!kmsan_internal_is_vmalloc_addr(vaddr) &&
!kmsan_internal_is_module_addr(vaddr))
return NULL;
page = vmalloc_to_page(vaddr);
if (pfn_valid(page_to_pfn(page)))
return page;
else
return NULL;
}
void kmsan_internal_check_memory(void *addr, size_t size,
const void __user *user_addr, int reason)
{
depot_stack_handle_t cur_origin = 0, new_origin = 0;
unsigned long addr64 = (unsigned long)addr;
depot_stack_handle_t *origin = NULL;
unsigned char *shadow = NULL;
int cur_off_start = -1;
int chunk_size;
size_t pos = 0;
if (!size)
return;
KMSAN_WARN_ON(!kmsan_metadata_is_contiguous(addr, size));
while (pos < size) {
chunk_size = min(size - pos,
PAGE_SIZE - ((addr64 + pos) % PAGE_SIZE));
shadow = kmsan_get_metadata((void *)(addr64 + pos),
KMSAN_META_SHADOW);
if (!shadow) {
/*
* This page is untracked. If there were uninitialized
* bytes before, report them.
*/
if (cur_origin) {
kmsan_enter_runtime();
kmsan_report(cur_origin, addr, size,
cur_off_start, pos - 1, user_addr,
reason);
kmsan_leave_runtime();
}
cur_origin = 0;
cur_off_start = -1;
pos += chunk_size;
continue;
}
for (int i = 0; i < chunk_size; i++) {
if (!shadow[i]) {
/*
* This byte is unpoisoned. If there were
* poisoned bytes before, report them.
*/
if (cur_origin) {
kmsan_enter_runtime();
kmsan_report(cur_origin, addr, size,
cur_off_start, pos + i - 1,
user_addr, reason);
kmsan_leave_runtime();
}
cur_origin = 0;
cur_off_start = -1;
continue;
}
origin = kmsan_get_metadata((void *)(addr64 + pos + i),
KMSAN_META_ORIGIN);
KMSAN_WARN_ON(!origin);
new_origin = *origin;
/*
* Encountered new origin - report the previous
* uninitialized range.
*/
if (cur_origin != new_origin) {
if (cur_origin) {
kmsan_enter_runtime();
kmsan_report(cur_origin, addr, size,
cur_off_start, pos + i - 1,
user_addr, reason);
kmsan_leave_runtime();
}
cur_origin = new_origin;
cur_off_start = pos + i;
}
}
pos += chunk_size;
}
KMSAN_WARN_ON(pos != size);
if (cur_origin) {
kmsan_enter_runtime();
kmsan_report(cur_origin, addr, size, cur_off_start, pos - 1,
user_addr, reason);
kmsan_leave_runtime();
}
}
bool kmsan_metadata_is_contiguous(void *addr, size_t size)
{
char *cur_shadow = NULL, *next_shadow = NULL, *cur_origin = NULL,
*next_origin = NULL;
u64 cur_addr = (u64)addr, next_addr = cur_addr + PAGE_SIZE;
depot_stack_handle_t *origin_p;
bool all_untracked = false;
if (!size)
return true;
/* The whole range belongs to the same page. */
if (ALIGN_DOWN(cur_addr + size - 1, PAGE_SIZE) ==
ALIGN_DOWN(cur_addr, PAGE_SIZE))
return true;
cur_shadow = kmsan_get_metadata((void *)cur_addr, /*is_origin*/ false);
if (!cur_shadow)
all_untracked = true;
cur_origin = kmsan_get_metadata((void *)cur_addr, /*is_origin*/ true);
if (all_untracked && cur_origin)
goto report;
for (; next_addr < (u64)addr + size;
cur_addr = next_addr, cur_shadow = next_shadow,
cur_origin = next_origin, next_addr += PAGE_SIZE) {
next_shadow = kmsan_get_metadata((void *)next_addr, false);
next_origin = kmsan_get_metadata((void *)next_addr, true);
if (all_untracked) {
if (next_shadow || next_origin)
goto report;
if (!next_shadow && !next_origin)
continue;
}
if (((u64)cur_shadow == ((u64)next_shadow - PAGE_SIZE)) &&
((u64)cur_origin == ((u64)next_origin - PAGE_SIZE)))
continue;
goto report;
}
return true;
report:
pr_err("%s: attempting to access two shadow page ranges.\n", __func__);
pr_err("Access of size %ld at %px.\n", size, addr);
pr_err("Addresses belonging to different ranges: %px and %px\n",
(void *)cur_addr, (void *)next_addr);
pr_err("page[0].shadow: %px, page[1].shadow: %px\n", cur_shadow,
next_shadow);
pr_err("page[0].origin: %px, page[1].origin: %px\n", cur_origin,
next_origin);
origin_p = kmsan_get_metadata(addr, KMSAN_META_ORIGIN);
if (origin_p) {
pr_err("Origin: %08x\n", *origin_p);
kmsan_print_origin(*origin_p);
} else {
pr_err("Origin: unavailable\n");
}
return false;
}
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