During boot, all non-reserved memblock memory is exposed to page_alloc
via memblock_free_pages->__free_pages_core(). This results in
kasan_free_pages() being called, which poisons that memory.
Poisoning all that memory lengthens boot time. The most noticeable effect
is observed with the HW_TAGS mode. A boot-time impact may potentially also
affect systems with large amount of RAM.
This patch changes the tag-based modes to not poison the memory during
the memblock->page_alloc transition.
An exception is made for KASAN_GENERIC. Since it marks all new memory as
accessible, not poisoning the memory released from memblock will lead to
KASAN missing invalid boot-time accesses to that memory.
With KASAN_SW_TAGS, as it uses the invalid 0xFE tag as the default tag
for all memory, it won't miss bad boot-time accesses even if the poisoning
of memblock memory is removed.
With KASAN_HW_TAGS, the default memory tags values are unspecified.
Therefore, if memblock poisoning is removed, this KASAN mode will miss
the mentioned type of boot-time bugs with a 1/16 probability. This is
taken as an acceptable trafe-off.
Internally, the poisoning is removed as follows. __free_pages_core() is
used when exposing fresh memory during system boot and when onlining
memory during hotplug. This patch adds a new FPI_SKIP_KASAN_POISON flag
and passes it to __free_pages_ok() through free_pages_prepare() from
__free_pages_core(). If FPI_SKIP_KASAN_POISON is set, kasan_free_pages()
is not called.
All memory allocated normally when the boot is over keeps getting
poisoned as usual.
Reviewed-by: Catalin Marinas <catalin.marinas@xxxxxxx>
Signed-off-by: Andrey Konovalov <andreyknvl@xxxxxxxxxx>
---
Changes v1->v2:
- Only drop memblock poisoning for tag-based KASAN modes.
---
mm/page_alloc.c | 45 ++++++++++++++++++++++++++++++++++-----------
1 file changed, 34 insertions(+), 11 deletions(-)
diff --git a/mm/page_alloc.c b/mm/page_alloc.c
index 0b55c9c95364..c89e7b107514 100644
--- a/mm/page_alloc.c
+++ b/mm/page_alloc.c
@@ -108,6 +108,17 @@ typedef int __bitwise fpi_t;
*/
#define FPI_TO_TAIL ((__force fpi_t)BIT(1))
+/*
+ * Don't poison memory with KASAN (only for the tag-based modes).
+ * During boot, all non-reserved memblock memory is exposed to page_alloc.
+ * Poisoning all that memory lengthens boot time, especially on systems with
+ * large amount of RAM. This flag is used to skip that poisoning.
+ * This is only done for the tag-based KASAN modes, as those are able to
+ * detect memory corruptions with the memory tags assigned by default.
+ * All memory allocated normally after boot gets poisoned as usual.
+ */
+#define FPI_SKIP_KASAN_POISON ((__force fpi_t)BIT(2))
+
/* prevent >1 _updater_ of zone percpu pageset ->high and ->batch fields */
static DEFINE_MUTEX(pcp_batch_high_lock);
#define MIN_PERCPU_PAGELIST_FRACTION (8)
@@ -384,10 +395,15 @@ static DEFINE_STATIC_KEY_TRUE(deferred_pages);
* on-demand allocation and then freed again before the deferred pages
* initialization is done, but this is not likely to happen.
*/
-static inline void kasan_free_nondeferred_pages(struct page *page, int order)
+static inline void kasan_free_nondeferred_pages(struct page *page, int order,
+ fpi_t fpi_flags)
{
- if (!static_branch_unlikely(&deferred_pages))
- kasan_free_pages(page, order);
+ if (static_branch_unlikely(&deferred_pages))
+ return;
+ if (!IS_ENABLED(CONFIG_KASAN_GENERIC) &&
+ (fpi_flags & FPI_SKIP_KASAN_POISON))
+ return;
+ kasan_free_pages(page, order);
}
/* Returns true if the struct page for the pfn is uninitialised */
@@ -438,7 +454,14 @@ defer_init(int nid, unsigned long pfn, unsigned long end_pfn)
return false;
}
#else
-#define kasan_free_nondeferred_pages(p, o) kasan_free_pages(p, o)
+static inline void kasan_free_nondeferred_pages(struct page *page, int order,
+ fpi_t fpi_flags)
+{
+ if (!IS_ENABLED(CONFIG_KASAN_GENERIC) &&
+ (fpi_flags & FPI_SKIP_KASAN_POISON))
+ return;
+ kasan_free_pages(page, order);
+}
static inline bool early_page_uninitialised(unsigned long pfn)
{
@@ -1216,7 +1239,7 @@ static void kernel_init_free_pages(struct page *page, int numpages)
}
static __always_inline bool free_pages_prepare(struct page *page,
- unsigned int order, bool check_free)
+ unsigned int order, bool check_free, fpi_t fpi_flags)
{
int bad = 0;
@@ -1290,7 +1313,7 @@ static __always_inline bool free_pages_prepare(struct page *page,
debug_pagealloc_unmap_pages(page, 1 << order);
- kasan_free_nondeferred_pages(page, order);
+ kasan_free_nondeferred_pages(page, order, fpi_flags);
return true;
}
@@ -1303,7 +1326,7 @@ static __always_inline bool free_pages_prepare(struct page *page,
*/
static bool free_pcp_prepare(struct page *page)
{
- return free_pages_prepare(page, 0, true);
+ return free_pages_prepare(page, 0, true, FPI_NONE);
}
static bool bulkfree_pcp_prepare(struct page *page)
@@ -1323,9 +1346,9 @@ static bool bulkfree_pcp_prepare(struct page *page)
static bool free_pcp_prepare(struct page *page)
{
if (debug_pagealloc_enabled_static())
- return free_pages_prepare(page, 0, true);
+ return free_pages_prepare(page, 0, true, FPI_NONE);
else
- return free_pages_prepare(page, 0, false);
+ return free_pages_prepare(page, 0, false, FPI_NONE);
}
static bool bulkfree_pcp_prepare(struct page *page)
@@ -1533,7 +1556,7 @@ static void __free_pages_ok(struct page *page, unsigned int order,
int migratetype;
unsigned long pfn = page_to_pfn(page);
- if (!free_pages_prepare(page, order, true))
+ if (!free_pages_prepare(page, order, true, fpi_flags))
return;
migratetype = get_pfnblock_migratetype(page, pfn);
@@ -1570,7 +1593,7 @@ void __free_pages_core(struct page *page, unsigned int order)
* Bypass PCP and place fresh pages right to the tail, primarily
* relevant for memory onlining.
*/
- __free_pages_ok(page, order, FPI_TO_TAIL);
+ __free_pages_ok(page, order, FPI_TO_TAIL | FPI_SKIP_KASAN_POISON);
}
#ifdef CONFIG_NEED_MULTIPLE_NODES
--
2.30.0.617.g56c4b15f3c-goog
