On Sun, Feb 26, 2023 at 4:20 PM Andrey Konovalov <andreyknvl@xxxxxxxxx> wrote: > > On Fri, Feb 24, 2023 at 7:51 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. > > This seems reasonable. > > > Signed-off-by: Peter Collingbourne <pcc@xxxxxxxxxx> > > Link: https://linux-review.googlesource.com/id/I57f825f2eaeaf7e8389d6cf4597c8a5821359838 > > --- > > I sent this independently of > > https://lore.kernel.org/all/20230224061550.177541-1-pcc@xxxxxxxxxx/ > > because I initially thought that the patches were independent. > > But moments after sending it, I realized that this patch depends on > > that one, because without that patch, this patch will end up disabling > > page poisoning altogether! But it's too late to turn them into a series > > now; I'll do that for v2. > > > > include/linux/page-flags.h | 9 --------- > > include/trace/events/mmflags.h | 9 +-------- > > mm/page_alloc.c | 28 ++++++++-------------------- > > 3 files changed, 9 insertions(+), 37 deletions(-) > > > > 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..c448694fc7e9 100644 > > --- a/include/trace/events/mmflags.h > > +++ b/include/trace/events/mmflags.h > > @@ -96,12 +96,6 @@ > > #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 +124,7 @@ 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/page_alloc.c b/mm/page_alloc.c > > index 7136c36c5d01..2509b8bde8d5 100644 > > --- a/mm/page_alloc.c > > +++ b/mm/page_alloc.c > > @@ -1380,7 +1380,7 @@ 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); > > + page_kasan_tag(page) == 0xff; > > Please also update the comment above should_skip_kasan_poison. Done in v2. > I think we can drop #3 and #4 from that comment and instead add a more > generic #3: "Page tags have not been assigned, as unpoisoning has been > skipped". I realized that the page tag will also be unassigned when the page is first being initialized, so I decided to be more explicit in the comment here about the circumstances where this will happen. I also took the opportunity to remove the FPI_SKIP_KASAN_POISON flag, since I realized that it is now also redundant with the page tag. > > } > > > > static void kernel_init_pages(struct page *page, int numpages) > > @@ -2511,22 +2511,13 @@ 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 (!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; > > + /* Take note that memory tags were set by KASAN. */ > > + reset_tags = false; > > } > > /* > > * If memory tags have not been set by KASAN, reset the page tags to > > @@ -2539,9 +2530,6 @@ inline void post_alloc_hook(struct page *page, unsigned int order, > > /* 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); > > With this removed, __GFP_SKIP_KASAN_POISON is no longer used and can > be removed too. Done in v2. Since the remaining flag will skip both poisoning and unpoisoning, I decided to rename it to GFP_SKIP_KASAN. Peter
