[PATCH v6 17/44] init: kmsan: call KMSAN initialization routines

Alexander Potapenko
2022-09-05T12:28:48Z

kmsan_init_shadow() scans the mappings created at boot time and creates
metadata pages for those mappings.

When the memblock allocator returns pages to pagealloc, we reserve 2/3
of those pages and use them as metadata for the remaining 1/3. Once KMSAN
starts, every page allocated by pagealloc has its associated shadow and
origin pages.

kmsan_initialize() initializes the bookkeeping for init_task and enables
KMSAN.

Signed-off-by: Alexander Potapenko <glider@google.com>
---
v2:
-- move mm/kmsan/init.c and kmsan_memblock_free_pages() to this patch
-- print a warning that KMSAN is a debugging tool (per Greg K-H's
request)

v4:
-- change sizeof(type) to sizeof(*ptr)
-- replace occurrences of |var| with @var
-- swap init: and kmsan: in the subject

v5:
-- address Marco Elver's comments
-- don't export initialization routines
-- use modern style for-loops
-- better name for struct page_pair
-- delete duplicate function prototypes

Link: https://linux-review.googlesource.com/id/I7bc53706141275914326df2345881ffe0cdd16bd
---
include/linux/kmsan.h | 36 +++++++
init/main.c | 3 +
mm/kmsan/Makefile | 3 +-
mm/kmsan/init.c | 235 ++++++++++++++++++++++++++++++++++++++++++
mm/kmsan/kmsan.h | 3 +
mm/kmsan/shadow.c | 34 ++++++
mm/page_alloc.c | 4 +
7 files changed, 317 insertions(+), 1 deletion(-)
create mode 100644 mm/kmsan/init.c

diff --git a/include/linux/kmsan.h b/include/linux/kmsan.h
index 354aee6f7b1a2..e00de976ee438 100644
--- a/include/linux/kmsan.h
+++ b/include/linux/kmsan.h
@@ -31,6 +31,28 @@ void kmsan_task_create(struct task_struct *task);
*/
void kmsan_task_exit(struct task_struct *task);

+/**
+ * kmsan_init_shadow() - Initialize KMSAN shadow at boot time.
+ *
+ * Allocate and initialize KMSAN metadata for early allocations.
+ */
+void __init kmsan_init_shadow(void);
+
+/**
+ * kmsan_init_runtime() - Initialize KMSAN state and enable KMSAN.
+ */
+void __init kmsan_init_runtime(void);
+
+/**
+ * kmsan_memblock_free_pages() - handle freeing of memblock pages.
+ * @page: struct page to free.
+ * @order: order of @page.
+ *
+ * Freed pages are either returned to buddy allocator or held back to be used
+ * as metadata pages.
+ */
+bool __init kmsan_memblock_free_pages(struct page *page, unsigned int order);
+
/**
* kmsan_alloc_page() - Notify KMSAN about an alloc_pages() call.
* @page: struct page pointer returned by alloc_pages().
@@ -152,6 +174,20 @@ void kmsan_iounmap_page_range(unsigned long start, unsigned long end);

#else

+static inline void kmsan_init_shadow(void)
+{
+}
+
+static inline void kmsan_init_runtime(void)
+{
+}
+
+static inline bool kmsan_memblock_free_pages(struct page *page,
+ unsigned int order)
+{
+ return true;
+}
+
static inline void kmsan_task_create(struct task_struct *task)
{
}
diff --git a/init/main.c b/init/main.c
index 1fe7942f5d4a8..3afed7bf9f683 100644
--- a/init/main.c
+++ b/init/main.c
@@ -34,6 +34,7 @@
#include <linux/percpu.h>
#include <linux/kmod.h>
#include <linux/kprobes.h>
+#include <linux/kmsan.h>
#include <linux/vmalloc.h>
#include <linux/kernel_stat.h>
#include <linux/start_kernel.h>
@@ -836,6 +837,7 @@ static void __init mm_init(void)
init_mem_debugging_and_hardening();
kfence_alloc_pool();
report_meminit();
+ kmsan_init_shadow();
stack_depot_early_init();
mem_init();
mem_init_print_info();
@@ -853,6 +855,7 @@ static void __init mm_init(void)
init_espfix_bsp();
/* Should be run after espfix64 is set up. */
pti_init();
+ kmsan_init_runtime();
}

#ifdef CONFIG_RANDOMIZE_KSTACK_OFFSET
diff --git a/mm/kmsan/Makefile b/mm/kmsan/Makefile
index 550ad8625e4f9..401acb1a491ce 100644
--- a/mm/kmsan/Makefile
+++ b/mm/kmsan/Makefile
@@ -3,7 +3,7 @@
# Makefile for KernelMemorySanitizer (KMSAN).
#
#
-obj-y := core.o instrumentation.o hooks.o report.o shadow.o
+obj-y := core.o instrumentation.o init.o hooks.o report.o shadow.o

KMSAN_SANITIZE := n
KCOV_INSTRUMENT := n
@@ -18,6 +18,7 @@ CFLAGS_REMOVE.o = $(CC_FLAGS_FTRACE)

CFLAGS_core.o := $(CC_FLAGS_KMSAN_RUNTIME)
CFLAGS_hooks.o := $(CC_FLAGS_KMSAN_RUNTIME)
+CFLAGS_init.o := $(CC_FLAGS_KMSAN_RUNTIME)
CFLAGS_instrumentation.o := $(CC_FLAGS_KMSAN_RUNTIME)
CFLAGS_report.o := $(CC_FLAGS_KMSAN_RUNTIME)
CFLAGS_shadow.o := $(CC_FLAGS_KMSAN_RUNTIME)
diff --git a/mm/kmsan/init.c b/mm/kmsan/init.c
new file mode 100644
index 0000000000000..7fb794242fad0
--- /dev/null
+++ b/mm/kmsan/init.c
@@ -0,0 +1,235 @@
+// SPDX-License-Identifier: GPL-2.0
+/*
+ * KMSAN initialization routines.
+ *
+ * Copyright (C) 2017-2021 Google LLC
+ * Author: Alexander Potapenko <glider@google.com>
+ *
+ */
+
+#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) || !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 = roundup(sizeof(pg_data_t), PAGE_SIZE);
+ 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[MAX_ORDER] __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_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);
+ }
+}
+
+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_ORDER - 1;
+ for (int i = MAX_ORDER - 1; 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;
+}
diff --git a/mm/kmsan/kmsan.h b/mm/kmsan/kmsan.h
index 04954b83c5d65..e064b4601af9d 100644
--- a/mm/kmsan/kmsan.h
+++ b/mm/kmsan/kmsan.h
@@ -66,6 +66,7 @@ struct shadow_origin_ptr {
struct shadow_origin_ptr kmsan_get_shadow_origin_ptr(void *addr, u64 size,
bool store);
void *kmsan_get_metadata(void *addr, bool is_origin);
+void __init kmsan_init_alloc_meta_for_range(void *start, void *end);

enum kmsan_bug_reason {
REASON_ANY,
@@ -186,6 +187,8 @@ void kmsan_internal_check_memory(void *addr, size_t size, const void *user_addr,
int reason);

struct page *kmsan_vmalloc_to_page_or_null(void *vaddr);
+void kmsan_setup_meta(struct page *page, struct page *shadow,
+ struct page *origin, int order);

/*
* kmsan_internal_is_module_addr() and kmsan_internal_is_vmalloc_addr() are
diff --git a/mm/kmsan/shadow.c b/mm/kmsan/shadow.c
index 8c81a059beea6..6e90a806a7045 100644
--- a/mm/kmsan/shadow.c
+++ b/mm/kmsan/shadow.c
@@ -258,3 +258,37 @@ void kmsan_vmap_pages_range_noflush(unsigned long start, unsigned long end,
kfree(s_pages);
kfree(o_pages);
}
+
+/* Allocate metadata for pages allocated at boot time. */
+void __init kmsan_init_alloc_meta_for_range(void *start, void *end)
+{
+ struct page *shadow_p, *origin_p;
+ void *shadow, *origin;
+ struct page *page;
+ u64 size;
+
+ 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 (u64 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;
+ }
+}
+
+void kmsan_setup_meta(struct page *page, struct page *shadow,
+ struct page *origin, int order)
+{
+ for (int i = 0; i < (1 << order); i++) {
+ set_no_shadow_origin_page(&shadow[i]);
+ set_no_shadow_origin_page(&origin[i]);
+ shadow_page_for(&page[i]) = &shadow[i];
+ origin_page_for(&page[i]) = &origin[i];
+ }
+}
diff --git a/mm/page_alloc.c b/mm/page_alloc.c
index d488dab76a6e8..b28093e3bb42a 100644
--- a/mm/page_alloc.c
+++ b/mm/page_alloc.c
@@ -1806,6 +1806,10 @@ void __init memblock_free_pages(struct page *page, unsigned long pfn,
{
if (early_page_uninitialised(pfn))
return;
+ if (!kmsan_memblock_free_pages(page, order)) {
+ /* KMSAN will take care of these pages. */
+ return;
+ }
__free_pages_core(page, order);
}

--
2.37.2.789.g6183377224-goog