Re: [PATCH v4 14/45] mm: kmsan: maintain KMSAN metadata for page operations

[Alexander Potapenko]

On Tue, Jul 12, 2022 at 2:21 PM Marco Elver <elver@xxxxxxxxxx> wrote:
>
> On Fri, 1 Jul 2022 at 16:23, Alexander Potapenko <glider@xxxxxxxxxx> 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@xxxxxxxxxx>
> > ---
> > 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Actually, the comment is a bit outdated.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

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