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

Matthew Wilcox
2021-03-20T00:36:35Z

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?

> + 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
>
>