| Message ID | 20230224065128.505605-1-pcc@google.com (mailing list archive) |
|---|---|
| State | New |
| Headers | show |
| Series | kasan: remove PG_skip_kasan_poison flag | expand |
On Fri, Feb 24, 2023 at 7:51 AM Peter Collingbourne <pcc@google.com> 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@google.com> > Link: https://linux-review.googlesource.com/id/I57f825f2eaeaf7e8389d6cf4597c8a5821359838 > --- > I sent this independently of > https://lore.kernel.org/all/20230224061550.177541-1-pcc@google.com/ > 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. 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". > } > > 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. > > set_page_owner(page, order, gfp_flags); > page_table_check_alloc(page, order); > -- > 2.39.2.637.g21b0678d19-goog >
On Sun, Feb 26, 2023 at 4:20 PM Andrey Konovalov <andreyknvl@gmail.com> wrote: > > On Fri, Feb 24, 2023 at 7:51 AM Peter Collingbourne <pcc@google.com> 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@google.com> > > Link: https://linux-review.googlesource.com/id/I57f825f2eaeaf7e8389d6cf4597c8a5821359838 > > --- > > I sent this independently of > > https://lore.kernel.org/all/20230224061550.177541-1-pcc@google.com/ > > 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
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; } 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); set_page_owner(page, order, gfp_flags); page_table_check_alloc(page, order);
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. Signed-off-by: Peter Collingbourne <pcc@google.com> Link: https://linux-review.googlesource.com/id/I57f825f2eaeaf7e8389d6cf4597c8a5821359838 --- I sent this independently of https://lore.kernel.org/all/20230224061550.177541-1-pcc@google.com/ 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(-)