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authorPeter Collingbourne <pcc@google.com>2023-03-10 05:29:14 +0100
committerAndrew Morton <akpm@linux-foundation.org>2023-03-29 01:20:16 +0200
commit0a54864f8dfb64b64c84c9db6ff70e0e93690a33 (patch)
tree00de1c53f4138a72acfca6559c7e66cc3ae54e3b /mm/page_alloc.c
parentio-mapping: don't disable preempt on RT in io_mapping_map_atomic_wc(). (diff)
downloadlinux-0a54864f8dfb64b64c84c9db6ff70e0e93690a33.tar.xz
linux-0a54864f8dfb64b64c84c9db6ff70e0e93690a33.zip
kasan: remove PG_skip_kasan_poison flag
Code inspection reveals that PG_skip_kasan_poison is redundant with kasantag, because the former is intended to be set iff the latter is the match-all tag. It can also be observed that it's basically pointless to poison pages which have kasantag=0, because any pages with this tag would have been pointed to by pointers with match-all tags, so poisoning the pages would have little to no effect in terms of bug detection. Therefore, change the condition in should_skip_kasan_poison() to check kasantag instead, and remove PG_skip_kasan_poison and associated flags. Link: https://lkml.kernel.org/r/20230310042914.3805818-3-pcc@google.com Link: https://linux-review.googlesource.com/id/I57f825f2eaeaf7e8389d6cf4597c8a5821359838 Signed-off-by: Peter Collingbourne <pcc@google.com> Reviewed-by: Andrey Konovalov <andreyknvl@gmail.com> Cc: Andrey Ryabinin <ryabinin.a.a@gmail.com> Cc: Catalin Marinas <catalin.marinas@arm.com> Cc: Evgenii Stepanov <eugenis@google.com> Cc: Vincenzo Frascino <vincenzo.frascino@arm.com> Cc: Will Deacon <will@kernel.org> Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Diffstat (limited to 'mm/page_alloc.c')
-rw-r--r--mm/page_alloc.c81
1 files changed, 30 insertions, 51 deletions
diff --git a/mm/page_alloc.c b/mm/page_alloc.c
index a109444e9f44..3737f9d58f5f 100644
--- a/mm/page_alloc.c
+++ b/mm/page_alloc.c
@@ -112,17 +112,6 @@ 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_HIGH_FRACTION (8)
@@ -1370,13 +1359,19 @@ out:
/*
* Skip KASAN memory poisoning when either:
*
- * 1. Deferred memory initialization has not yet completed,
- * see the explanation below.
- * 2. Skipping poisoning is requested via FPI_SKIP_KASAN_POISON,
- * see the comment next to it.
- * 3. Skipping poisoning is requested via __GFP_SKIP_KASAN_POISON,
- * see the comment next to it.
- * 4. The allocation is excluded from being checked due to sampling,
+ * 1. For generic KASAN: deferred memory initialization has not yet completed.
+ * Tag-based KASAN modes skip pages freed via deferred memory initialization
+ * using page tags instead (see below).
+ * 2. For tag-based KASAN modes: the page has a match-all KASAN tag, indicating
+ * that error detection is disabled for accesses via the page address.
+ *
+ * Pages will have match-all tags in the following circumstances:
+ *
+ * 1. Pages are being initialized for the first time, including during deferred
+ * memory init; see the call to page_kasan_tag_reset in __init_single_page.
+ * 2. The allocation was not unpoisoned due to __GFP_SKIP_KASAN, with the
+ * exception of pages unpoisoned by kasan_unpoison_vmalloc.
+ * 3. The allocation was excluded from being checked due to sampling,
* see the call to kasan_unpoison_pages.
*
* Poisoning pages during deferred memory init will greatly lengthen the
@@ -1392,10 +1387,10 @@ out:
*/
static inline bool should_skip_kasan_poison(struct page *page, fpi_t fpi_flags)
{
- return deferred_pages_enabled() ||
- (!IS_ENABLED(CONFIG_KASAN_GENERIC) &&
- (fpi_flags & FPI_SKIP_KASAN_POISON)) ||
- PageSkipKASanPoison(page);
+ if (IS_ENABLED(CONFIG_KASAN_GENERIC))
+ return deferred_pages_enabled();
+
+ return page_kasan_tag(page) == 0xff;
}
static void kernel_init_pages(struct page *page, int numpages)
@@ -1730,7 +1725,7 @@ 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 | FPI_SKIP_KASAN_POISON);
+ __free_pages_ok(page, order, FPI_TO_TAIL);
}
#ifdef CONFIG_NUMA
@@ -2396,9 +2391,9 @@ static inline bool should_skip_kasan_unpoison(gfp_t flags)
/*
* With hardware tag-based KASAN enabled, skip if this has been
- * requested via __GFP_SKIP_KASAN_UNPOISON.
+ * requested via __GFP_SKIP_KASAN.
*/
- return flags & __GFP_SKIP_KASAN_UNPOISON;
+ return flags & __GFP_SKIP_KASAN;
}
static inline bool should_skip_init(gfp_t flags)
@@ -2417,7 +2412,6 @@ inline void post_alloc_hook(struct page *page, unsigned int order,
bool init = !want_init_on_free() && want_init_on_alloc(gfp_flags) &&
!should_skip_init(gfp_flags);
bool zero_tags = init && (gfp_flags & __GFP_ZEROTAGS);
- bool reset_tags = true;
int i;
set_page_private(page, 0);
@@ -2451,37 +2445,22 @@ inline void post_alloc_hook(struct page *page, unsigned int order,
/* Take note that memory was initialized by the loop above. */
init = false;
}
- if (!should_skip_kasan_unpoison(gfp_flags)) {
- /* Try unpoisoning (or setting tags) and initializing memory. */
- if (kasan_unpoison_pages(page, order, init)) {
- /* Take note that memory was initialized by KASAN. */
- if (kasan_has_integrated_init())
- init = false;
- /* Take note that memory tags were set by KASAN. */
- reset_tags = false;
- } else {
- /*
- * KASAN decided to exclude this allocation from being
- * (un)poisoned due to sampling. Make KASAN skip
- * poisoning when the allocation is freed.
- */
- SetPageSkipKASanPoison(page);
- }
- }
- /*
- * If memory tags have not been set by KASAN, reset the page tags to
- * ensure page_address() dereferencing does not fault.
- */
- if (reset_tags) {
+ if (!should_skip_kasan_unpoison(gfp_flags) &&
+ kasan_unpoison_pages(page, order, init)) {
+ /* Take note that memory was initialized by KASAN. */
+ if (kasan_has_integrated_init())
+ init = false;
+ } else {
+ /*
+ * If memory tags have not been set by KASAN, reset the page
+ * tags to ensure page_address() dereferencing does not fault.
+ */
for (i = 0; i != 1 << order; ++i)
page_kasan_tag_reset(page + i);
}
/* If memory is still not initialized, initialize it now. */
if (init)
kernel_init_pages(page, 1 << order);
- /* Propagate __GFP_SKIP_KASAN_POISON to page flags. */
- if (kasan_hw_tags_enabled() && (gfp_flags & __GFP_SKIP_KASAN_POISON))
- SetPageSkipKASanPoison(page);
set_page_owner(page, order, gfp_flags);
page_table_check_alloc(page, order);