On Tue, Feb 28, 2023 at 12:48 PM Andrey Konovalov <andreyknvl@xxxxxxxxx> wrote: > > On Tue, Feb 28, 2023 at 7:32 AM Peter Collingbourne <pcc@xxxxxxxxxx> wrote: > > > > 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@xxxxxxxxxx> > > Link: https://linux-review.googlesource.com/id/I57f825f2eaeaf7e8389d6cf4597c8a5821359838 > > --- > > 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 | 28 +++++------- > > include/linux/page-flags.h | 9 ---- > > include/trace/events/mmflags.h | 12 +----- > > mm/kasan/hw_tags.c | 2 +- > > mm/page_alloc.c | 79 +++++++++++++--------------------- > > mm/vmalloc.c | 2 +- > > 6 files changed, 44 insertions(+), 88 deletions(-) > > > > diff --git a/include/linux/gfp_types.h b/include/linux/gfp_types.h > > index 5088637fe5c2..9bd45cdd19ac 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 +232,22 @@ 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 and > > + * poisoning on page deallocation. Typically used for userspace and vmalloc > > + * pages. Only effective in HW_TAGS mode. > > This is not entirely correct: for vmalloc pages, this flag doesn't > result in poisoning being skipped, as the memory is unpoisoned and > page tags are assigned by kasan_unpoison_vmalloc. I see. I somehow missed that vmalloc was setting the tag itself. > How about something like this: > > %__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. Yes, that sounds reasonable. Done in v3. > > */ > > #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 +330,7 @@ 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 a7e3a3405520..74f81a52e7e1 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 9db52bc4ce19..232bc8efc98e 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 > > @@ -96,12 +95,6 @@ > > #define IF_HAVE_PG_ARCH_X(flag,string) > > #endif > > > > -#ifdef CONFIG_KASAN_HW_TAGS > > -#define IF_HAVE_PG_SKIP_KASAN_POISON(flag,string) ,{1UL << flag, string} > > -#else > > -#define IF_HAVE_PG_SKIP_KASAN_POISON(flag,string) > > -#endif > > - > > #define __def_pageflag_names \ > > {1UL << PG_locked, "locked" }, \ > > {1UL << PG_waiters, "waiters" }, \ > > @@ -130,8 +123,7 @@ IF_HAVE_PG_HWPOISON(PG_hwpoison, "hwpoison" ) \ > > IF_HAVE_PG_IDLE(PG_young, "young" ) \ > > IF_HAVE_PG_IDLE(PG_idle, "idle" ) \ > > IF_HAVE_PG_ARCH_X(PG_arch_2, "arch_2" ) \ > > -IF_HAVE_PG_ARCH_X(PG_arch_3, "arch_3" ) \ > > -IF_HAVE_PG_SKIP_KASAN_POISON(PG_skip_kasan_poison, "skip_kasan_poison") > > +IF_HAVE_PG_ARCH_X(PG_arch_3, "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 7136c36c5d01..960e0edd413d 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) > > @@ -1355,13 +1344,19 @@ 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, > > + * 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: the page has a match-all KASAN tag, indicating > > For tag-based KASAN modes: ... Done in v3. > > + * that error detection is disabled for accesses via the page address. > > + * > > + * Pages will have match-all tags in the following circumstances: > > + * > > + * 1. Skipping poisoning is requested via __GFP_SKIP_KASAN, > > * see the comment next to it. > > According to the vmalloc thing I mentioned above, let's reword this to: > > The allocation was not unpoisoned due to __GFP_SKIP_KASAN, with the > exception of pages unpoisoned by kasan_unpoison_vmalloc. Done in v3. > > - * 4. The allocation is excluded from being checked due to sampling, > > + * 2. 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. > > Let's put this item first in the list. > > > + * 3. The allocation is excluded from being checked due to sampling, Done in v3. > "is" -> "was" possibly sounds better with "was" in #1. Done in v3. Peter
