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Date: Wed, 7 Sep 2016 11:54:11 -0700
From: Sinclair Yeh <syeh@...are.com>
To: Kees Cook <keescook@...omium.org>
CC: Thomas Hellstrom <thellstrom@...are.com>,
Rik van Riel <riel@...hat.com>,
Laura Abbott <labbott@...hat.com>,
VMware Graphics <linux-graphics-maintainer@...are.com>,
Vinson Lee <vlee@...edesktop.org>,
Linus Torvalds <torvalds@...ux-foundation.org>,
Vladimir Davydov <vdavydov.dev@...il.com>,
Johannes Weiner <hannes@...xchg.org>,
"Andy Lutomirski" <luto@...nel.org>, <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH v2] usercopy: remove page-spanning test for now
Reviewed-by: Sinclair Yeh <syeh@...are.com>
On Wed, Sep 07, 2016 at 11:08:45AM -0700, Kees Cook wrote:
> A custom allocator without __GFP_COMP that copies to userspace has been
> found in vmw_execbuf_process[1], so this disables the page-span checker
> by placing it behind a CONFIG for future work where such things can be
> tracked down later.
>
> [1] https://urldefense.proofpoint.com/v2/url?u=https-3A__bugzilla.redhat.com_show-5Fbug.cgi-3Fid-3D1373326&d=CwIBAg&c=Sqcl0Ez6M0X8aeM67LKIiDJAXVeAw-YihVMNtXt-uEs&r=w9Iu3o4zAy-3-s8MFvrNSQ&m=HmnBFNgZxprKMPy51P5NjJYN3A5FrdjyzaM817eexKU&s=Htqh5qkhK5mXIdzTCYiqCaZU1R98sOatRFgsoDbGOzw&e=
>
> Reported-by: Vinson Lee <vlee@...edesktop.org>
> Fixes: f5509cc18daa ("mm: Hardened usercopy")
> Signed-off-by: Kees Cook <keescook@...omium.org>
> ---
> v2:
> - split logic into separate function entirely, torvalds
> ---
> mm/usercopy.c | 61 ++++++++++++++++++++++++++++++++------------------------
> security/Kconfig | 11 ++++++++++
> 2 files changed, 46 insertions(+), 26 deletions(-)
>
> diff --git a/mm/usercopy.c b/mm/usercopy.c
> index a3cc3052f830..089328f2b920 100644
> --- a/mm/usercopy.c
> +++ b/mm/usercopy.c
> @@ -134,31 +134,16 @@ static inline const char *check_bogus_address(const void *ptr, unsigned long n)
> return NULL;
> }
>
> -static inline const char *check_heap_object(const void *ptr, unsigned long n,
> - bool to_user)
> +/* Checks for allocs that are marked in some way as spanning multiple pages. */
> +static inline const char *check_page_span(const void *ptr, unsigned long n,
> + struct page *page, bool to_user)
> {
> - struct page *page, *endpage;
> +#ifdef CONFIG_HARDENED_USERCOPY_PAGESPAN
> const void *end = ptr + n - 1;
> + struct page *endpage;
> bool is_reserved, is_cma;
>
> /*
> - * Some architectures (arm64) return true for virt_addr_valid() on
> - * vmalloced addresses. Work around this by checking for vmalloc
> - * first.
> - */
> - if (is_vmalloc_addr(ptr))
> - return NULL;
> -
> - if (!virt_addr_valid(ptr))
> - return NULL;
> -
> - page = virt_to_head_page(ptr);
> -
> - /* Check slab allocator for flags and size. */
> - if (PageSlab(page))
> - return __check_heap_object(ptr, n, page);
> -
> - /*
> * 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.
> @@ -186,7 +171,7 @@ static inline const char *check_heap_object(const void *ptr, unsigned long n,
> ((unsigned long)end & (unsigned long)PAGE_MASK)))
> return NULL;
>
> - /* Allow if start and end are inside the same compound page. */
> + /* Allow if fully inside the same compound (__GFP_COMP) page. */
> endpage = virt_to_head_page(end);
> if (likely(endpage == page))
> return NULL;
> @@ -199,20 +184,44 @@ static inline const char *check_heap_object(const void *ptr, unsigned long n,
> is_reserved = PageReserved(page);
> is_cma = is_migrate_cma_page(page);
> if (!is_reserved && !is_cma)
> - goto reject;
> + return "<spans multiple pages>";
>
> for (ptr += PAGE_SIZE; ptr <= end; ptr += PAGE_SIZE) {
> page = virt_to_head_page(ptr);
> if (is_reserved && !PageReserved(page))
> - goto reject;
> + return "<spans Reserved and non-Reserved pages>";
> if (is_cma && !is_migrate_cma_page(page))
> - goto reject;
> + return "<spans CMA and non-CMA pages>";
> }
> +#endif
>
> return NULL;
> +}
> +
> +static inline const char *check_heap_object(const void *ptr, unsigned long n,
> + bool to_user)
> +{
> + struct page *page;
> +
> + /*
> + * Some architectures (arm64) return true for virt_addr_valid() on
> + * vmalloced addresses. Work around this by checking for vmalloc
> + * first.
> + */
> + if (is_vmalloc_addr(ptr))
> + return NULL;
> +
> + if (!virt_addr_valid(ptr))
> + return NULL;
> +
> + page = virt_to_head_page(ptr);
> +
> + /* Check slab allocator for flags and size. */
> + if (PageSlab(page))
> + return __check_heap_object(ptr, n, page);
>
> -reject:
> - return "<spans multiple pages>";
> + /* Verify object does not incorrectly span multiple pages. */
> + return check_page_span(ptr, n, page, to_user);
> }
>
> /*
> diff --git a/security/Kconfig b/security/Kconfig
> index da10d9b573a4..2dfc0ce4083e 100644
> --- a/security/Kconfig
> +++ b/security/Kconfig
> @@ -147,6 +147,17 @@ config HARDENED_USERCOPY
> or are part of the kernel text. This kills 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 !COMPILE_TEST
> + 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.
> +
> source security/selinux/Kconfig
> source security/smack/Kconfig
> source security/tomoyo/Kconfig
> --
> 2.7.4
>
>
> --
> Kees Cook
> Nexus Security
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