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    SubjectRe: [PATCH v4 14/45] mm: kmsan: maintain KMSAN metadata for page operations
    On Tue, Jul 12, 2022 at 2:21 PM Marco Elver <elver@google.com> wrote:
    >
    > On Fri, 1 Jul 2022 at 16:23, Alexander Potapenko <glider@google.com> wrote:
    > >
    > > Insert KMSAN hooks that make the necessary bookkeeping changes:
    > > - poison page shadow and origins in alloc_pages()/free_page();
    > > - clear page shadow and origins in clear_page(), copy_user_highpage();
    > > - copy page metadata in copy_highpage(), wp_page_copy();
    > > - handle vmap()/vunmap()/iounmap();
    > >
    > > Signed-off-by: Alexander Potapenko <glider@google.com>
    > > ---
    > > v2:
    > > -- move page metadata hooks implementation here
    > > -- remove call to kmsan_memblock_free_pages()
    > >
    > > v3:
    > > -- use PAGE_SHIFT in kmsan_ioremap_page_range()
    > >
    > > v4:
    > > -- change sizeof(type) to sizeof(*ptr)
    > > -- replace occurrences of |var| with @var
    > > -- swap mm: and kmsan: in the subject
    > > -- drop __no_sanitize_memory from clear_page()
    > >
    > > Link: https://linux-review.googlesource.com/id/I6d4f53a0e7eab46fa29f0348f3095d9f2e326850
    > > ---
    > > arch/x86/include/asm/page_64.h | 12 ++++
    > > arch/x86/mm/ioremap.c | 3 +
    > > include/linux/highmem.h | 3 +
    > > include/linux/kmsan.h | 123 +++++++++++++++++++++++++++++++++
    > > mm/internal.h | 6 ++
    > > mm/kmsan/hooks.c | 87 +++++++++++++++++++++++
    > > mm/kmsan/shadow.c | 114 ++++++++++++++++++++++++++++++
    > > mm/memory.c | 2 +
    > > mm/page_alloc.c | 11 +++
    > > mm/vmalloc.c | 20 +++++-
    > > 10 files changed, 379 insertions(+), 2 deletions(-)
    > >
    > > diff --git a/arch/x86/include/asm/page_64.h b/arch/x86/include/asm/page_64.h
    > > index baa70451b8df5..227dd33eb4efb 100644
    > > --- a/arch/x86/include/asm/page_64.h
    > > +++ b/arch/x86/include/asm/page_64.h
    > > @@ -45,14 +45,26 @@ void clear_page_orig(void *page);
    > > void clear_page_rep(void *page);
    > > void clear_page_erms(void *page);
    > >
    > > +/* This is an assembly header, avoid including too much of kmsan.h */
    >
    > All of this code is under an "#ifndef __ASSEMBLY__" guard, does it matter?
    Actually, the comment is a bit outdated. kmsan-checks.h doesn't
    introduce any unnecessary declarations and can be used here.

    > > +#ifdef CONFIG_KMSAN
    > > +void kmsan_unpoison_memory(const void *addr, size_t size);
    > > +#endif
    > > static inline void clear_page(void *page)
    > > {
    > > +#ifdef CONFIG_KMSAN
    > > + /* alternative_call_2() changes @page. */
    > > + void *page_copy = page;
    > > +#endif
    > > alternative_call_2(clear_page_orig,
    > > clear_page_rep, X86_FEATURE_REP_GOOD,
    > > clear_page_erms, X86_FEATURE_ERMS,
    > > "=D" (page),
    > > "0" (page)
    > > : "cc", "memory", "rax", "rcx");
    > > +#ifdef CONFIG_KMSAN
    > > + /* Clear KMSAN shadow for the pages that have it. */
    > > + kmsan_unpoison_memory(page_copy, PAGE_SIZE);
    >
    > What happens if this is called before the alternative-call? Could this
    > (in the interest of simplicity) be moved above it? And if you used the
    > kmsan-checks.h header, it also doesn't need any "ifdef CONFIG_KMSAN"
    > anymore.

    Good idea, that'll work.

    > > +#endif
    > > }



    --
    Alexander Potapenko
    Software Engineer

    Google Germany GmbH
    Erika-Mann-Straße, 33
    80636 München

    Geschäftsführer: Paul Manicle, Liana Sebastian
    Registergericht und -nummer: Hamburg, HRB 86891
    Sitz der Gesellschaft: Hamburg

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