[PATCH v4 2/2] kasan: remove PG_skip_kasan_poison flag
Peter Collingbourne
pcc at google.com
Thu Mar 9 20:29:14 PST 2023
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.
Signed-off-by: Peter Collingbourne <pcc at google.com>
Link: https://linux-review.googlesource.com/id/I57f825f2eaeaf7e8389d6cf4597c8a5821359838
Reviewed-by: Andrey Konovalov <andreyknvl at gmail.com>
---
v4:
- rebased to linux-next
v3:
- update comments
v2:
- also remove GFP_SKIP_KASAN_POISON and FPI_SKIP_KASAN_POISON
- rename GFP_SKIP_KASAN_UNPOISON to GFP_SKIP_KASAN
- update comments
- simplify control flow by removing reset_tags
include/linux/gfp_types.h | 30 ++++++-------
include/linux/page-flags.h | 9 ----
include/trace/events/mmflags.h | 13 +-----
mm/kasan/hw_tags.c | 2 +-
mm/page_alloc.c | 81 +++++++++++++---------------------
mm/vmalloc.c | 2 +-
6 files changed, 47 insertions(+), 90 deletions(-)
diff --git a/include/linux/gfp_types.h b/include/linux/gfp_types.h
index 5088637fe5c2..6583a58670c5 100644
--- a/include/linux/gfp_types.h
+++ b/include/linux/gfp_types.h
@@ -47,16 +47,14 @@ typedef unsigned int __bitwise gfp_t;
#define ___GFP_ACCOUNT 0x400000u
#define ___GFP_ZEROTAGS 0x800000u
#ifdef CONFIG_KASAN_HW_TAGS
-#define ___GFP_SKIP_ZERO 0x1000000u
-#define ___GFP_SKIP_KASAN_UNPOISON 0x2000000u
-#define ___GFP_SKIP_KASAN_POISON 0x4000000u
+#define ___GFP_SKIP_ZERO 0x1000000u
+#define ___GFP_SKIP_KASAN 0x2000000u
#else
-#define ___GFP_SKIP_ZERO 0
-#define ___GFP_SKIP_KASAN_UNPOISON 0
-#define ___GFP_SKIP_KASAN_POISON 0
+#define ___GFP_SKIP_ZERO 0
+#define ___GFP_SKIP_KASAN 0
#endif
#ifdef CONFIG_LOCKDEP
-#define ___GFP_NOLOCKDEP 0x8000000u
+#define ___GFP_NOLOCKDEP 0x4000000u
#else
#define ___GFP_NOLOCKDEP 0
#endif
@@ -234,25 +232,24 @@ typedef unsigned int __bitwise gfp_t;
* memory tags at the same time as zeroing memory has minimal additional
* performace impact.
*
- * %__GFP_SKIP_KASAN_UNPOISON makes KASAN skip unpoisoning on page allocation.
- * Only effective in HW_TAGS mode.
- *
- * %__GFP_SKIP_KASAN_POISON makes KASAN skip poisoning on page deallocation.
- * Typically, used for userspace pages. Only effective in HW_TAGS mode.
+ * %__GFP_SKIP_KASAN makes KASAN skip unpoisoning on page allocation.
+ * Used for userspace and vmalloc pages; the latter are unpoisoned by
+ * kasan_unpoison_vmalloc instead. For userspace pages, results in
+ * poisoning being skipped as well, see should_skip_kasan_poison for
+ * details. Only effective in HW_TAGS mode.
*/
#define __GFP_NOWARN ((__force gfp_t)___GFP_NOWARN)
#define __GFP_COMP ((__force gfp_t)___GFP_COMP)
#define __GFP_ZERO ((__force gfp_t)___GFP_ZERO)
#define __GFP_ZEROTAGS ((__force gfp_t)___GFP_ZEROTAGS)
#define __GFP_SKIP_ZERO ((__force gfp_t)___GFP_SKIP_ZERO)
-#define __GFP_SKIP_KASAN_UNPOISON ((__force gfp_t)___GFP_SKIP_KASAN_UNPOISON)
-#define __GFP_SKIP_KASAN_POISON ((__force gfp_t)___GFP_SKIP_KASAN_POISON)
+#define __GFP_SKIP_KASAN ((__force gfp_t)___GFP_SKIP_KASAN)
/* Disable lockdep for GFP context tracking */
#define __GFP_NOLOCKDEP ((__force gfp_t)___GFP_NOLOCKDEP)
/* Room for N __GFP_FOO bits */
-#define __GFP_BITS_SHIFT (27 + IS_ENABLED(CONFIG_LOCKDEP))
+#define __GFP_BITS_SHIFT (26 + IS_ENABLED(CONFIG_LOCKDEP))
#define __GFP_BITS_MASK ((__force gfp_t)((1 << __GFP_BITS_SHIFT) - 1))
/**
@@ -335,8 +332,7 @@ typedef unsigned int __bitwise gfp_t;
#define GFP_DMA __GFP_DMA
#define GFP_DMA32 __GFP_DMA32
#define GFP_HIGHUSER (GFP_USER | __GFP_HIGHMEM)
-#define GFP_HIGHUSER_MOVABLE (GFP_HIGHUSER | __GFP_MOVABLE | \
- __GFP_SKIP_KASAN_POISON | __GFP_SKIP_KASAN_UNPOISON)
+#define GFP_HIGHUSER_MOVABLE (GFP_HIGHUSER | __GFP_MOVABLE | __GFP_SKIP_KASAN)
#define GFP_TRANSHUGE_LIGHT ((GFP_HIGHUSER_MOVABLE | __GFP_COMP | \
__GFP_NOMEMALLOC | __GFP_NOWARN) & ~__GFP_RECLAIM)
#define GFP_TRANSHUGE (GFP_TRANSHUGE_LIGHT | __GFP_DIRECT_RECLAIM)
diff --git a/include/linux/page-flags.h b/include/linux/page-flags.h
index 57287102c5bd..dcda20c47b8f 100644
--- a/include/linux/page-flags.h
+++ b/include/linux/page-flags.h
@@ -135,9 +135,6 @@ enum pageflags {
#ifdef CONFIG_ARCH_USES_PG_ARCH_X
PG_arch_2,
PG_arch_3,
-#endif
-#ifdef CONFIG_KASAN_HW_TAGS
- PG_skip_kasan_poison,
#endif
__NR_PAGEFLAGS,
@@ -594,12 +591,6 @@ TESTCLEARFLAG(Young, young, PF_ANY)
PAGEFLAG(Idle, idle, PF_ANY)
#endif
-#ifdef CONFIG_KASAN_HW_TAGS
-PAGEFLAG(SkipKASanPoison, skip_kasan_poison, PF_HEAD)
-#else
-PAGEFLAG_FALSE(SkipKASanPoison, skip_kasan_poison)
-#endif
-
/*
* PageReported() is used to track reported free pages within the Buddy
* allocator. We can use the non-atomic version of the test and set
diff --git a/include/trace/events/mmflags.h b/include/trace/events/mmflags.h
index b28218b7998e..b63e7c0fbbe5 100644
--- a/include/trace/events/mmflags.h
+++ b/include/trace/events/mmflags.h
@@ -55,8 +55,7 @@
#ifdef CONFIG_KASAN_HW_TAGS
#define __def_gfpflag_names_kasan , \
gfpflag_string(__GFP_SKIP_ZERO), \
- gfpflag_string(__GFP_SKIP_KASAN_POISON), \
- gfpflag_string(__GFP_SKIP_KASAN_UNPOISON)
+ gfpflag_string(__GFP_SKIP_KASAN)
#else
#define __def_gfpflag_names_kasan
#endif
@@ -96,13 +95,6 @@
#define IF_HAVE_PG_ARCH_X(_name)
#endif
-#ifdef CONFIG_KASAN_HW_TAGS
-#define IF_HAVE_PG_SKIP_KASAN_POISON(_name) \
- ,{1UL << PG_##_name, __stringify(_name)}
-#else
-#define IF_HAVE_PG_SKIP_KASAN_POISON(_name)
-#endif
-
#define DEF_PAGEFLAG_NAME(_name) { 1UL << PG_##_name, __stringify(_name) }
#define __def_pageflag_names \
@@ -133,8 +125,7 @@ IF_HAVE_PG_HWPOISON(hwpoison) \
IF_HAVE_PG_IDLE(idle) \
IF_HAVE_PG_IDLE(young) \
IF_HAVE_PG_ARCH_X(arch_2) \
-IF_HAVE_PG_ARCH_X(arch_3) \
-IF_HAVE_PG_SKIP_KASAN_POISON(skip_kasan_poison)
+IF_HAVE_PG_ARCH_X(arch_3)
#define show_page_flags(flags) \
(flags) ? __print_flags(flags, "|", \
diff --git a/mm/kasan/hw_tags.c b/mm/kasan/hw_tags.c
index d1bcb0205327..bb4f56e5bdec 100644
--- a/mm/kasan/hw_tags.c
+++ b/mm/kasan/hw_tags.c
@@ -318,7 +318,7 @@ void *__kasan_unpoison_vmalloc(const void *start, unsigned long size,
* Thus, for VM_ALLOC mappings, hardware tag-based KASAN only tags
* the first virtual mapping, which is created by vmalloc().
* Tagging the page_alloc memory backing that vmalloc() allocation is
- * skipped, see ___GFP_SKIP_KASAN_UNPOISON.
+ * skipped, see ___GFP_SKIP_KASAN.
*
* For non-VM_ALLOC allocations, page_alloc memory is tagged as usual.
*/
diff --git a/mm/page_alloc.c b/mm/page_alloc.c
index c58ebf21ce63..680a4d76460e 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 @@ static int free_tail_pages_check(struct page *head_page, struct page *page)
/*
* 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 @@ static int free_tail_pages_check(struct page *head_page, struct page *page)
*/
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);
diff --git a/mm/vmalloc.c b/mm/vmalloc.c
index bef6cf2b4d46..5e60e9792cbf 100644
--- a/mm/vmalloc.c
+++ b/mm/vmalloc.c
@@ -3188,7 +3188,7 @@ void *__vmalloc_node_range(unsigned long size, unsigned long align,
* pages backing VM_ALLOC mapping. Memory is instead
* poisoned and zeroed by kasan_unpoison_vmalloc().
*/
- gfp_mask |= __GFP_SKIP_KASAN_UNPOISON | __GFP_SKIP_ZERO;
+ gfp_mask |= __GFP_SKIP_KASAN | __GFP_SKIP_ZERO;
}
/* Take note that the mapping is PAGE_KERNEL. */
--
2.40.0.rc1.284.g88254d51c5-goog
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