From: Andrey Konovalov <andreyknvl@xxxxxxxxxx> Subject: kasan, page_alloc: allow skipping unpoisoning for HW_TAGS Add a new GFP flag __GFP_SKIP_KASAN_UNPOISON that allows skipping KASAN poisoning for page_alloc allocations. The flag is only effective with HW_TAGS KASAN. This flag will be used by vmalloc code for page_alloc allocations backing vmalloc() mappings in a following patch. The reason to skip KASAN poisoning for these pages in page_alloc is because vmalloc code will be poisoning them instead. Also reword the comment for __GFP_SKIP_KASAN_POISON. Link: https://lkml.kernel.org/r/35c97d77a704f6ff971dd3bfe4be95855744108e.1643047180.git.andreyknvl@xxxxxxxxxx Signed-off-by: Andrey Konovalov <andreyknvl@xxxxxxxxxx> Acked-by: Marco Elver <elver@xxxxxxxxxx> Cc: Alexander Potapenko <glider@xxxxxxxxxx> Cc: Andrey Ryabinin <ryabinin.a.a@xxxxxxxxx> Cc: Catalin Marinas <catalin.marinas@xxxxxxx> Cc: Dmitry Vyukov <dvyukov@xxxxxxxxxx> Cc: Evgenii Stepanov <eugenis@xxxxxxxxxx> Cc: Mark Rutland <mark.rutland@xxxxxxx> Cc: Peter Collingbourne <pcc@xxxxxxxxxx> Cc: Vincenzo Frascino <vincenzo.frascino@xxxxxxx> Cc: Will Deacon <will@xxxxxxxxxx> Signed-off-by: Andrew Morton <akpm@xxxxxxxxxxxxxxxxxxxx> --- include/linux/gfp.h | 21 +++++++++++++-------- include/trace/events/mmflags.h | 5 +++-- mm/page_alloc.c | 31 ++++++++++++++++++++++--------- 3 files changed, 38 insertions(+), 19 deletions(-) --- a/include/linux/gfp.h~kasan-page_alloc-allow-skipping-unpoisoning-for-hw_tags +++ a/include/linux/gfp.h @@ -55,12 +55,14 @@ struct vm_area_struct; #define ___GFP_ACCOUNT 0x400000u #define ___GFP_ZEROTAGS 0x800000u #ifdef CONFIG_KASAN_HW_TAGS -#define ___GFP_SKIP_KASAN_POISON 0x1000000u +#define ___GFP_SKIP_KASAN_UNPOISON 0x1000000u +#define ___GFP_SKIP_KASAN_POISON 0x2000000u #else +#define ___GFP_SKIP_KASAN_UNPOISON 0 #define ___GFP_SKIP_KASAN_POISON 0 #endif #ifdef CONFIG_LOCKDEP -#define ___GFP_NOLOCKDEP 0x2000000u +#define ___GFP_NOLOCKDEP 0x4000000u #else #define ___GFP_NOLOCKDEP 0 #endif @@ -241,22 +243,25 @@ struct vm_area_struct; * intended for optimization: setting memory tags at the same time as zeroing * memory has minimal additional performace impact. * - * %__GFP_SKIP_KASAN_POISON returns a page which does not need to be poisoned - * on deallocation. Typically used for userspace pages. Currently only has an - * effect in HW tags mode. + * %__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. */ #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_KASAN_POISON ((__force gfp_t)___GFP_SKIP_KASAN_POISON) +#define __GFP_SKIP_KASAN_UNPOISON ((__force gfp_t)___GFP_SKIP_KASAN_UNPOISON) +#define __GFP_SKIP_KASAN_POISON ((__force gfp_t)___GFP_SKIP_KASAN_POISON) /* Disable lockdep for GFP context tracking */ #define __GFP_NOLOCKDEP ((__force gfp_t)___GFP_NOLOCKDEP) /* Room for N __GFP_FOO bits */ -#define __GFP_BITS_SHIFT (24 + \ - IS_ENABLED(CONFIG_KASAN_HW_TAGS) + \ +#define __GFP_BITS_SHIFT (24 + \ + 2 * IS_ENABLED(CONFIG_KASAN_HW_TAGS) + \ IS_ENABLED(CONFIG_LOCKDEP)) #define __GFP_BITS_MASK ((__force gfp_t)((1 << __GFP_BITS_SHIFT) - 1)) --- a/include/trace/events/mmflags.h~kasan-page_alloc-allow-skipping-unpoisoning-for-hw_tags +++ a/include/trace/events/mmflags.h @@ -52,8 +52,9 @@ {(unsigned long)__GFP_ZEROTAGS, "__GFP_ZEROTAGS"} \ #ifdef CONFIG_KASAN_HW_TAGS -#define __def_gfpflag_names_kasan \ - , {(unsigned long)__GFP_SKIP_KASAN_POISON, "__GFP_SKIP_KASAN_POISON"} +#define __def_gfpflag_names_kasan , \ + {(unsigned long)__GFP_SKIP_KASAN_POISON, "__GFP_SKIP_KASAN_POISON"}, \ + {(unsigned long)__GFP_SKIP_KASAN_UNPOISON, "__GFP_SKIP_KASAN_UNPOISON"} #else #define __def_gfpflag_names_kasan #endif --- a/mm/page_alloc.c~kasan-page_alloc-allow-skipping-unpoisoning-for-hw_tags +++ a/mm/page_alloc.c @@ -2343,6 +2343,26 @@ static inline bool check_new_pcp(struct } #endif /* CONFIG_DEBUG_VM */ +static inline bool should_skip_kasan_unpoison(gfp_t flags, bool init_tags) +{ + /* Don't skip if a software KASAN mode is enabled. */ + if (IS_ENABLED(CONFIG_KASAN_GENERIC) || + IS_ENABLED(CONFIG_KASAN_SW_TAGS)) + return false; + + /* Skip, if hardware tag-based KASAN is not enabled. */ + if (!kasan_hw_tags_enabled()) + return true; + + /* + * With hardware tag-based KASAN enabled, skip if either: + * + * 1. Memory tags have already been cleared via tag_clear_highpage(). + * 2. Skipping has been requested via __GFP_SKIP_KASAN_UNPOISON. + */ + return init_tags || (flags & __GFP_SKIP_KASAN_UNPOISON); +} + inline void post_alloc_hook(struct page *page, unsigned int order, gfp_t gfp_flags) { @@ -2382,15 +2402,8 @@ inline void post_alloc_hook(struct page /* Note that memory is already initialized by the loop above. */ init = false; } - /* - * If either a software KASAN mode is enabled, or, - * in the case of hardware tag-based KASAN, - * if memory tags have not been cleared via tag_clear_highpage(). - */ - if (IS_ENABLED(CONFIG_KASAN_GENERIC) || - IS_ENABLED(CONFIG_KASAN_SW_TAGS) || - kasan_hw_tags_enabled() && !init_tags) { - /* Mark shadow memory or set memory tags. */ + if (!should_skip_kasan_unpoison(gfp_flags, init_tags)) { + /* Unpoison shadow memory or set memory tags. */ kasan_unpoison_pages(page, order, init); /* Note that memory is already initialized by KASAN. */ _
