Re: [PATCH v3] mm/gup: check page posion status for coredump.

Aili Yao
2021-03-22T03:41:27Z

On Sat, 20 Mar 2021 00:35:16 +0000
Matthew Wilcox <willy@infradead.org> wrote:

> On Fri, Mar 19, 2021 at 10:44:37AM +0800, Aili Yao wrote:
> > +++ b/mm/gup.c
> > @@ -1536,6 +1536,10 @@ struct page *get_dump_page(unsigned long addr)
> > FOLL_FORCE | FOLL_DUMP | FOLL_GET);
> > if (locked)
> > mmap_read_unlock(mm);
> > +
> > + if (ret == 1 && is_page_poisoned(page))
> > + return NULL;
> > +
> > return (ret == 1) ? page : NULL;
> > }
> > #endif /* CONFIG_ELF_CORE */
> > diff --git a/mm/internal.h b/mm/internal.h
> > index 25d2b2439..902d993 100644
> > --- a/mm/internal.h
> > +++ b/mm/internal.h
> > @@ -97,6 +97,27 @@ static inline void set_page_refcounted(struct page *page)
> > set_page_count(page, 1);
> > }
> >
> > +/*
> > + * When kernel touch the user page, the user page may be have been marked
> > + * poison but still mapped in user space, if without this page, the kernel
> > + * can guarantee the data integrity and operation success, the kernel is
> > + * better to check the posion status and avoid touching it, be good not to
> > + * panic, coredump for process fatal signal is a sample case matching this
> > + * scenario. Or if kernel can't guarantee the data integrity, it's better
> > + * not to call this function, let kernel touch the poison page and get to
> > + * panic.
> > + */
> > +static inline bool is_page_poisoned(struct page *page)
> > +{
> > + if (page != NULL) {
>
> Why are you checking page for NULL here? How can it possibly be NULL?

For this get_dump_page() case, it can't be NULL, I thougt may other place
will call this function and may not guarantee this, But yes, kernel is a more
safer place and checking page NULL is not a common behavior.

Better to remove it, Thanks you very much for pointing this!

> > + if (PageHWPoison(page))
> > + return true;
> > + else if (PageHuge(page) && PageHWPoison(compound_head(page)))
> > + return true;
> > + }
> > + return 0;
> > +}
> > +
> > extern unsigned long highest_memmap_pfn;
> >
> > /*
> > --
> > 1.8.3.1
> >
> >
--
Thanks!
Aili Yao