On Mon, Jan 10, 2022 at 11:15:30PM +0000, Matthew Wilcox (Oracle) wrote:
> There isn't enough information to make this a useful check any more;
> the useful parts of it were moved in earlier patches, so remove this
> set of checks now.
>
> Signed-off-by: Matthew Wilcox (Oracle) <willy@xxxxxxxxxxxxx>
Thank you!
Acked-by: Kees Cook <keescook@xxxxxxxxxxxx>
> ---
> mm/usercopy.c | 61 ------------------------------------------------
> security/Kconfig | 13 +----------
> 2 files changed, 1 insertion(+), 73 deletions(-)
>
> diff --git a/mm/usercopy.c b/mm/usercopy.c
> index e1cb98087a05..94831945d9e7 100644
> --- a/mm/usercopy.c
> +++ b/mm/usercopy.c
> @@ -158,64 +158,6 @@ static inline void check_bogus_address(const unsigned long ptr, unsigned long n,
> usercopy_abort("null address", NULL, to_user, ptr, n);
> }
>
> -/* Checks for allocs that are marked in some way as spanning multiple pages. */
> -static inline void check_page_span(const void *ptr, unsigned long n,
> - struct page *page, bool to_user)
> -{
> -#ifdef CONFIG_HARDENED_USERCOPY_PAGESPAN
> - const void *end = ptr + n - 1;
> - bool is_reserved, is_cma;
> -
> - /*
> - * Sometimes the kernel data regions are not marked Reserved (see
> - * check below). And sometimes [_sdata,_edata) does not cover
> - * rodata and/or bss, so check each range explicitly.
> - */
> -
> - /* Allow reads of kernel rodata region (if not marked as Reserved). */
> - if (ptr >= (const void *)__start_rodata &&
> - end <= (const void *)__end_rodata) {
> - if (!to_user)
> - usercopy_abort("rodata", NULL, to_user, 0, n);
> - return;
> - }
> -
> - /* Allow kernel data region (if not marked as Reserved). */
> - if (ptr >= (const void *)_sdata && end <= (const void *)_edata)
> - return;
> -
> - /* Allow kernel bss region (if not marked as Reserved). */
> - if (ptr >= (const void *)__bss_start &&
> - end <= (const void *)__bss_stop)
> - return;
> -
> - /* Is the object wholly within one base page? */
> - if (likely(((unsigned long)ptr & (unsigned long)PAGE_MASK) ==
> - ((unsigned long)end & (unsigned long)PAGE_MASK)))
> - return;
> -
> - /*
> - * Reject if range is entirely either Reserved (i.e. special or
> - * device memory), or CMA. Otherwise, reject since the object spans
> - * several independently allocated pages.
> - */
> - is_reserved = PageReserved(page);
> - is_cma = is_migrate_cma_page(page);
> - if (!is_reserved && !is_cma)
> - usercopy_abort("spans multiple pages", NULL, to_user, 0, n);
> -
> - for (ptr += PAGE_SIZE; ptr <= end; ptr += PAGE_SIZE) {
> - page = virt_to_head_page(ptr);
> - if (is_reserved && !PageReserved(page))
> - usercopy_abort("spans Reserved and non-Reserved pages",
> - NULL, to_user, 0, n);
> - if (is_cma && !is_migrate_cma_page(page))
> - usercopy_abort("spans CMA and non-CMA pages", NULL,
> - to_user, 0, n);
> - }
> -#endif
> -}
> -
> static inline void check_heap_object(const void *ptr, unsigned long n,
> bool to_user)
> {
> @@ -257,9 +199,6 @@ static inline void check_heap_object(const void *ptr, unsigned long n,
> unsigned long offset = ptr - folio_address(folio);
> if (offset + n > folio_size(folio))
> usercopy_abort("page alloc", NULL, to_user, offset, n);
> - } else {
> - /* Verify object does not incorrectly span multiple pages. */
> - check_page_span(ptr, n, folio_page(folio, 0), to_user);
> }
> }
>
> diff --git a/security/Kconfig b/security/Kconfig
> index 0b847f435beb..5b289b329a51 100644
> --- a/security/Kconfig
> +++ b/security/Kconfig
> @@ -160,20 +160,9 @@ config HARDENED_USERCOPY
> copy_from_user() functions) by rejecting memory ranges that
> are larger than the specified heap object, span multiple
> separately allocated pages, are not on the process stack,
> - or are part of the kernel text. This kills entire classes
> + or are part of the kernel text. This prevents entire classes
> of heap overflow exploits and similar kernel memory exposures.
>
> -config HARDENED_USERCOPY_PAGESPAN
> - bool "Refuse to copy allocations that span multiple pages"
> - depends on HARDENED_USERCOPY
> - depends on EXPERT
> - help
> - When a multi-page allocation is done without __GFP_COMP,
> - hardened usercopy will reject attempts to copy it. There are,
> - however, several cases of this in the kernel that have not all
> - been removed. This config is intended to be used only while
> - trying to find such users.
> -
> config FORTIFY_SOURCE
> bool "Harden common str/mem functions against buffer overflows"
> depends on ARCH_HAS_FORTIFY_SOURCE
> --
> 2.33.0
>
--
Kees Cook
