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kasan: clean up kasan_cache_create

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Reorganize the code to avoid nested if/else checks to improve the
readability.

Also drop the confusing comments about KMALLOC_MAX_SIZE checks: they are
relevant for both SLUB and SLAB (originally, the comments likely confused
KMALLOC_MAX_SIZE with KMALLOC_MAX_CACHE_SIZE).

Link: https://lkml.kernel.org/r/20231221183540.168428-1-andrey.konovalov@linux.dev
Fixes: a5989d4ed4 ("kasan: improve free meta storage in Generic KASAN")
Signed-off-by: Andrey Konovalov <andreyknvl@google.com>
Reviewed-by: Marco Elver <elver@google.com>
Cc: Alexander Potapenko <glider@google.com>
Cc: Andrey Ryabinin <ryabinin.a.a@gmail.com>
Cc: Dmitry Vyukov <dvyukov@google.com>
Cc: Juntong Deng <juntong.deng@outlook.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
This commit is contained in:
Andrey Konovalov 2023-12-21 19:35:37 +01:00 committed by Andrew Morton
parent 4e397274e1
commit f6940e8adc
1 changed files with 39 additions and 28 deletions
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57
mm/kasan/generic.c
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@ -382,16 +382,11 @@ void kasan_cache_create(struct kmem_cache *cache, unsigned int *size,
ok_size = *size;
/* Add alloc meta into redzone. */
/* Add alloc meta into the redzone. */
cache->kasan_info.alloc_meta_offset = *size;
*size += sizeof(struct kasan_alloc_meta);
/*
* If alloc meta doesn't fit, don't add it.
* This can only happen with SLAB, as it has KMALLOC_MAX_SIZE equal
* to KMALLOC_MAX_CACHE_SIZE and doesn't fall back to page_alloc for
* larger sizes.
*/
/* If alloc meta doesn't fit, don't add it. */
if (*size > KMALLOC_MAX_SIZE) {
cache->kasan_info.alloc_meta_offset = 0;
*size = ok_size;
@ -402,36 +397,52 @@ void kasan_cache_create(struct kmem_cache *cache, unsigned int *size,
orig_alloc_meta_offset = cache->kasan_info.alloc_meta_offset;
/*
* Add free meta into redzone when it's not possible to store
* Store free meta in the redzone when it's not possible to store
* it in the object. This is the case when:
* 1. Object is SLAB_TYPESAFE_BY_RCU, which means that it can
* be touched after it was freed, or
* 2. Object has a constructor, which means it's expected to
* retain its content until the next allocation, or
* 3. Object is too small and SLUB DEBUG is enabled. Avoid
* free meta that exceeds the object size corrupts the
* SLUB DEBUG metadata.
* Otherwise cache->kasan_info.free_meta_offset = 0 is implied.
* If the object is smaller than the free meta and SLUB DEBUG
* is not enabled, it is still possible to store part of the
* free meta in the object.
* retain its content until the next allocation.
*/
if ((cache->flags & SLAB_TYPESAFE_BY_RCU) || cache->ctor) {
cache->kasan_info.free_meta_offset = *size;
*size += sizeof(struct kasan_free_meta);
} else if (cache->object_size < sizeof(struct kasan_free_meta)) {
if (__slub_debug_enabled()) {
cache->kasan_info.free_meta_offset = *size;
*size += sizeof(struct kasan_free_meta);
} else {
goto free_meta_added;
}
/*
* Otherwise, if the object is large enough to contain free meta,
* store it within the object.
*/
if (sizeof(struct kasan_free_meta) <= cache->object_size) {
/* cache->kasan_info.free_meta_offset = 0 is implied. */
goto free_meta_added;
}
/*
* For smaller objects, store the beginning of free meta within the
* object and the end in the redzone. And thus shift the location of
* alloc meta to free up space for free meta.
* This is only possible when slub_debug is disabled, as otherwise
* the end of free meta will overlap with slub_debug metadata.
*/
if (!__slub_debug_enabled()) {
rem_free_meta_size = sizeof(struct kasan_free_meta) -
cache->object_size;
*size += rem_free_meta_size;
if (cache->kasan_info.alloc_meta_offset != 0)
cache->kasan_info.alloc_meta_offset += rem_free_meta_size;
}
goto free_meta_added;
}
/*
* If the object is small and slub_debug is enabled, store free meta
* in the redzone after alloc meta.
*/
cache->kasan_info.free_meta_offset = *size;
*size += sizeof(struct kasan_free_meta);
free_meta_added:
/* If free meta doesn't fit, don't add it. */
if (*size > KMALLOC_MAX_SIZE) {
cache->kasan_info.free_meta_offset = KASAN_NO_FREE_META;
@ -441,7 +452,7 @@ void kasan_cache_create(struct kmem_cache *cache, unsigned int *size,
/* Calculate size with optimal redzone. */
optimal_size = cache->object_size + optimal_redzone(cache->object_size);
/* Limit it with KMALLOC_MAX_SIZE (relevant for SLAB only). */
/* Limit it with KMALLOC_MAX_SIZE. */
if (optimal_size > KMALLOC_MAX_SIZE)
optimal_size = KMALLOC_MAX_SIZE;
/* Use optimal size if the size with added metas is not large enough. */