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Message-ID: <0f980e84-b587-3d9e-3c26-ad57f947c08b@redhat.com>
Date: Mon, 25 Jul 2016 12:16:24 -0700
From: Laura Abbott <labbott@...hat.com>
To: Kees Cook <keescook@...omium.org>, kernel-hardening@...ts.openwall.com
Cc: Laura Abbott <labbott@...oraproject.org>,
Balbir Singh <bsingharora@...il.com>, Daniel Micay <danielmicay@...il.com>,
Josh Poimboeuf <jpoimboe@...hat.com>, Rik van Riel <riel@...hat.com>,
Casey Schaufler <casey@...aufler-ca.com>, PaX Team <pageexec@...email.hu>,
Brad Spengler <spender@...ecurity.net>, Russell King
<linux@...linux.org.uk>, Catalin Marinas <catalin.marinas@....com>,
Will Deacon <will.deacon@....com>, Ard Biesheuvel
<ard.biesheuvel@...aro.org>,
Benjamin Herrenschmidt <benh@...nel.crashing.org>,
Michael Ellerman <mpe@...erman.id.au>, Tony Luck <tony.luck@...el.com>,
Fenghua Yu <fenghua.yu@...el.com>, "David S. Miller" <davem@...emloft.net>,
x86@...nel.org, Christoph Lameter <cl@...ux.com>,
Pekka Enberg <penberg@...nel.org>, David Rientjes <rientjes@...gle.com>,
Joonsoo Kim <iamjoonsoo.kim@....com>,
Andrew Morton <akpm@...ux-foundation.org>, Andy Lutomirski
<luto@...nel.org>, Borislav Petkov <bp@...e.de>,
Mathias Krause <minipli@...glemail.com>, Jan Kara <jack@...e.cz>,
Vitaly Wool <vitalywool@...il.com>, Andrea Arcangeli <aarcange@...hat.com>,
Dmitry Vyukov <dvyukov@...gle.com>, linux-arm-kernel@...ts.infradead.org,
linux-ia64@...r.kernel.org, linuxppc-dev@...ts.ozlabs.org,
sparclinux@...r.kernel.org, linux-arch@...r.kernel.org, linux-mm@...ck.org,
linux-kernel@...r.kernel.org
Subject: Re: [PATCH v4 12/12] mm: SLUB hardened usercopy support
On 07/20/2016 01:27 PM, Kees Cook wrote:
> Under CONFIG_HARDENED_USERCOPY, this adds object size checking to the
> SLUB allocator to catch any copies that may span objects. Includes a
> redzone handling fix discovered by Michael Ellerman.
>
> Based on code from PaX and grsecurity.
>
> Signed-off-by: Kees Cook <keescook@...omium.org>
> Tested-by: Michael Ellerman <mpe@...erman.id.au>
> ---
> init/Kconfig | 1 +
> mm/slub.c | 36 ++++++++++++++++++++++++++++++++++++
> 2 files changed, 37 insertions(+)
>
> diff --git a/init/Kconfig b/init/Kconfig
> index 798c2020ee7c..1c4711819dfd 100644
> --- a/init/Kconfig
> +++ b/init/Kconfig
> @@ -1765,6 +1765,7 @@ config SLAB
>
> config SLUB
> bool "SLUB (Unqueued Allocator)"
> + select HAVE_HARDENED_USERCOPY_ALLOCATOR
> help
> SLUB is a slab allocator that minimizes cache line usage
> instead of managing queues of cached objects (SLAB approach).
> diff --git a/mm/slub.c b/mm/slub.c
> index 825ff4505336..7dee3d9a5843 100644
> --- a/mm/slub.c
> +++ b/mm/slub.c
> @@ -3614,6 +3614,42 @@ void *__kmalloc_node(size_t size, gfp_t flags, int node)
> EXPORT_SYMBOL(__kmalloc_node);
> #endif
>
> +#ifdef CONFIG_HARDENED_USERCOPY
> +/*
> + * Rejects objects that are incorrectly sized.
> + *
> + * Returns NULL if check passes, otherwise const char * to name of cache
> + * to indicate an error.
> + */
> +const char *__check_heap_object(const void *ptr, unsigned long n,
> + struct page *page)
> +{
> + struct kmem_cache *s;
> + unsigned long offset;
> + size_t object_size;
> +
> + /* Find object and usable object size. */
> + s = page->slab_cache;
> + object_size = slab_ksize(s);
> +
> + /* Find offset within object. */
> + offset = (ptr - page_address(page)) % s->size;
> +
> + /* Adjust for redzone and reject if within the redzone. */
> + if (kmem_cache_debug(s) && s->flags & SLAB_RED_ZONE) {
> + if (offset < s->red_left_pad)
> + return s->name;
> + offset -= s->red_left_pad;
> + }
> +
> + /* Allow address range falling entirely within object size. */
> + if (offset <= object_size && n <= object_size - offset)
> + return NULL;
> +
> + return s->name;
> +}
> +#endif /* CONFIG_HARDENED_USERCOPY */
> +
I compared this against what check_valid_pointer does for SLUB_DEBUG
checking. I was hoping we could utilize that function to avoid
duplication but a) __check_heap_object needs to allow accesses anywhere
in the object, not just the beginning b) accessing page->objects
is racy without the addition of locking in SLUB_DEBUG.
Still, the ptr < page_address(page) check from __check_heap_object would
be good to add to avoid generating garbage large offsets and trying to
infer C math.
diff --git a/mm/slub.c b/mm/slub.c
index 7dee3d9..5370e4f 100644
--- a/mm/slub.c
+++ b/mm/slub.c
@@ -3632,6 +3632,9 @@ const char *__check_heap_object(const void *ptr, unsigned long n,
s = page->slab_cache;
object_size = slab_ksize(s);
+ if (ptr < page_address(page))
+ return s->name;
+
/* Find offset within object. */
offset = (ptr - page_address(page)) % s->size;
With that, you can add
Reviwed-by: Laura Abbott <labbott@...hat.com>
> static size_t __ksize(const void *object)
> {
> struct page *page;
>
Thanks,
Laura
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