[PATCH v8 1/2] mm: security: introduce init_on_alloc=1 and init_on_free=1 boot options
Qian Cai
cai at lca.pw
Wed Jun 26 18:15:49 UTC 2019
On Wed, 2019-06-26 at 14:19 +0200, Alexander Potapenko wrote:
> The new options are needed to prevent possible information leaks and
> make control-flow bugs that depend on uninitialized values more
> deterministic.
>
> This is expected to be on-by-default on Android and Chrome OS. And it
> gives the opportunity for anyone else to use it under distros too via
> the boot args. (The init_on_free feature is regularly requested by
> folks where memory forensics is included in their threat models.)
>
> init_on_alloc=1 makes the kernel initialize newly allocated pages and heap
> objects with zeroes. Initialization is done at allocation time at the
> places where checks for __GFP_ZERO are performed.
>
> init_on_free=1 makes the kernel initialize freed pages and heap objects
> with zeroes upon their deletion. This helps to ensure sensitive data
> doesn't leak via use-after-free accesses.
>
> Both init_on_alloc=1 and init_on_free=1 guarantee that the allocator
> returns zeroed memory. The two exceptions are slab caches with
> constructors and SLAB_TYPESAFE_BY_RCU flag. Those are never
> zero-initialized to preserve their semantics.
>
> Both init_on_alloc and init_on_free default to zero, but those defaults
> can be overridden with CONFIG_INIT_ON_ALLOC_DEFAULT_ON and
> CONFIG_INIT_ON_FREE_DEFAULT_ON.
>
> If either SLUB poisoning or page poisoning is enabled, we disable
> init_on_alloc and init_on_free so that initialization doesn't interfere
> with debugging.
>
> Slowdown for the new features compared to init_on_free=0,
> init_on_alloc=0:
>
> hackbench, init_on_free=1: +7.62% sys time (st.err 0.74%)
> hackbench, init_on_alloc=1: +7.75% sys time (st.err 2.14%)
>
> Linux build with -j12, init_on_free=1: +8.38% wall time (st.err 0.39%)
> Linux build with -j12, init_on_free=1: +24.42% sys time (st.err 0.52%)
> Linux build with -j12, init_on_alloc=1: -0.13% wall time (st.err 0.42%)
> Linux build with -j12, init_on_alloc=1: +0.57% sys time (st.err 0.40%)
>
> The slowdown for init_on_free=0, init_on_alloc=0 compared to the
> baseline is within the standard error.
>
> The new features are also going to pave the way for hardware memory
> tagging (e.g. arm64's MTE), which will require both on_alloc and on_free
> hooks to set the tags for heap objects. With MTE, tagging will have the
> same cost as memory initialization.
>
> Although init_on_free is rather costly, there are paranoid use-cases where
> in-memory data lifetime is desired to be minimized. There are various
> arguments for/against the realism of the associated threat models, but
> given that we'll need the infrastructure for MTE anyway, and there are
> people who want wipe-on-free behavior no matter what the performance cost,
> it seems reasonable to include it in this series.
>
> Signed-off-by: Alexander Potapenko <glider at google.com>
> Acked-by: Kees Cook <keescook at chromium.org>
> To: Andrew Morton <akpm at linux-foundation.org>
> To: Christoph Lameter <cl at linux.com>
> To: Kees Cook <keescook at chromium.org>
> Cc: Masahiro Yamada <yamada.masahiro at socionext.com>
> Cc: Michal Hocko <mhocko at kernel.org>
> Cc: James Morris <jmorris at namei.org>
> Cc: "Serge E. Hallyn" <serge at hallyn.com>
> Cc: Nick Desaulniers <ndesaulniers at google.com>
> Cc: Kostya Serebryany <kcc at google.com>
> Cc: Dmitry Vyukov <dvyukov at google.com>
> Cc: Sandeep Patil <sspatil at android.com>
> Cc: Laura Abbott <labbott at redhat.com>
> Cc: Randy Dunlap <rdunlap at infradead.org>
> Cc: Jann Horn <jannh at google.com>
> Cc: Mark Rutland <mark.rutland at arm.com>
> Cc: Marco Elver <elver at google.com>
> Cc: Qian Cai <cai at lca.pw>
> Cc: linux-mm at kvack.org
> Cc: linux-security-module at vger.kernel.org
> Cc: kernel-hardening at lists.openwall.com
> Signed-off-by: Andrew Morton <akpm at linux-foundation.org>
> ---
> v2:
> - unconditionally initialize pages in kernel_init_free_pages()
> - comment from Randy Dunlap: drop 'default false' lines from
> Kconfig.hardening
> v3:
> - don't call kernel_init_free_pages() from memblock_free_pages()
> - adopted some Kees' comments for the patch description
> v4:
> - use NULL instead of 0 in slab_alloc_node() (found by kbuild test robot)
> - don't write to NULL object in slab_alloc_node() (found by Android
> testing)
> v5:
> - adjusted documentation wording as suggested by Kees
> - disable SLAB_POISON if auto-initialization is on
> - don't wipe RCU cache allocations made without __GFP_ZERO
> - dropped SLOB support
> v7:
> - rebase the patch, added the Acked-by: tag
> v8:
> - addressed comments by Michal Hocko: revert kernel/kexec_core.c and
> apply initialization in dma_pool_free()
> - disable init_on_alloc/init_on_free if slab poisoning or page
> poisoning are enabled, as requested by Qian Cai
> - skip the redzone when initializing a freed heap object, as requested
> by Qian Cai and Kees Cook
> - use s->offset to address the freeptr (suggested by Kees Cook)
> - updated the patch description, added Signed-off-by: tag
> ---
> .../admin-guide/kernel-parameters.txt | 9 +++
> drivers/infiniband/core/uverbs_ioctl.c | 2 +-
> include/linux/mm.h | 22 ++++++
> mm/dmapool.c | 4 +-
> mm/page_alloc.c | 71 +++++++++++++++++--
> mm/slab.c | 16 ++++-
> mm/slab.h | 19 +++++
> mm/slub.c | 43 +++++++++--
> net/core/sock.c | 2 +-
> security/Kconfig.hardening | 29 ++++++++
> 10 files changed, 199 insertions(+), 18 deletions(-)
>
> diff --git a/Documentation/admin-guide/kernel-parameters.txt
> b/Documentation/admin-guide/kernel-parameters.txt
> index 138f6664b2e2..84ee1121a2b9 100644
> --- a/Documentation/admin-guide/kernel-parameters.txt
> +++ b/Documentation/admin-guide/kernel-parameters.txt
> @@ -1673,6 +1673,15 @@
>
> initrd= [BOOT] Specify the location of the initial
> ramdisk
>
> + init_on_alloc= [MM] Fill newly allocated pages and heap
> objects with
> + zeroes.
> + Format: 0 | 1
> + Default set by CONFIG_INIT_ON_ALLOC_DEFAULT_ON.
> +
> + init_on_free= [MM] Fill freed pages and heap objects with
> zeroes.
> + Format: 0 | 1
> + Default set by CONFIG_INIT_ON_FREE_DEFAULT_ON.
> +
> init_pkru= [x86] Specify the default memory protection keys
> rights
> register contents for all processes. 0x55555554 by
> default (disallow access to all but pkey 0). Can
> diff --git a/drivers/infiniband/core/uverbs_ioctl.c
> b/drivers/infiniband/core/uverbs_ioctl.c
> index 829b0c6944d8..61758201d9b2 100644
> --- a/drivers/infiniband/core/uverbs_ioctl.c
> +++ b/drivers/infiniband/core/uverbs_ioctl.c
> @@ -127,7 +127,7 @@ __malloc void *_uverbs_alloc(struct uverbs_attr_bundle
> *bundle, size_t size,
> res = (void *)pbundle->internal_buffer + pbundle->internal_used;
> pbundle->internal_used =
> ALIGN(new_used, sizeof(*pbundle->internal_buffer));
> - if (flags & __GFP_ZERO)
> + if (want_init_on_alloc(flags))
> memset(res, 0, size);
> return res;
> }
> diff --git a/include/linux/mm.h b/include/linux/mm.h
> index dd0b5f4e1e45..96be2604f313 100644
> --- a/include/linux/mm.h
> +++ b/include/linux/mm.h
> @@ -2696,6 +2696,28 @@ static inline void kernel_poison_pages(struct page
> *page, int numpages,
> int enable) { }
> #endif
>
> +#ifdef CONFIG_INIT_ON_ALLOC_DEFAULT_ON
> +DECLARE_STATIC_KEY_TRUE(init_on_alloc);
> +#else
> +DECLARE_STATIC_KEY_FALSE(init_on_alloc);
> +#endif
> +static inline bool want_init_on_alloc(gfp_t flags)
> +{
> + if (static_branch_unlikely(&init_on_alloc))
> + return true;
> + return flags & __GFP_ZERO;
> +}
> +
> +#ifdef CONFIG_INIT_ON_FREE_DEFAULT_ON
> +DECLARE_STATIC_KEY_TRUE(init_on_free);
> +#else
> +DECLARE_STATIC_KEY_FALSE(init_on_free);
> +#endif
> +static inline bool want_init_on_free(void)
> +{
> + return static_branch_unlikely(&init_on_free);
> +}
> +
> extern bool _debug_pagealloc_enabled;
>
> static inline bool debug_pagealloc_enabled(void)
Do those really necessary need to be static keys?
Adding either init_on_free=0 or init_on_alloc=0 to the kernel cmdline will
generate a warning with kernels built with clang.
[ 0.000000] static_key_disable(): static key 'init_on_free+0x0/0x4' used
before call to jump_label_init()
[ 0.000000] WARNING: CPU: 0 PID: 0 at ./include/linux/jump_label.h:317
early_init_on_free+0x1c0/0x200
[ 0.000000] Modules linked in:
[ 0.000000] CPU: 0 PID: 0 Comm: swapper Not tainted 5.2.0-rc6-next-20190626+
#9
[ 0.000000] pstate: 60000089 (nZCv daIf -PAN -UAO)
[ 0.000000] pc : early_init_on_free+0x1c0/0x200
[ 0.000000] lr : early_init_on_free+0x1c0/0x200
[ 0.000000] sp : ffff100012c07df0
[ 0.000000] x29: ffff100012c07e20 x28: ffff1000110a01ec
[ 0.000000] x27: 000000000000005f x26: ffff100011716cd0
[ 0.000000] x25: ffff100010d36166 x24: ffff100010d3615d
[ 0.000000] x23: ffff100010d364b5 x22: ffff1000117164a0
[ 0.000000] x21: 0000000000000000 x20: 0000000000000000
[ 0.000000] x19: 0000000000000000 x18: 000000000000002e
[ 0.000000] x17: 000000000000000f x16: 0000000000000040
[ 0.000000] x15: 0000000000000000 x14: 6c61632065726f66
[ 0.000000] x13: 6562206465737520 x12: 273478302f307830
[ 0.000000] x11: 0000000000000000 x10: 0000000000000000
[ 0.000000] x9 : 0000000000000000 x8 : 0000000000000000
[ 0.000000] x7 : 6d756a206f74206c x6 : ffff100014426625
[ 0.000000] x5 : ffff100012c07b28 x4 : 0000000000000007
[ 0.000000] x3 : ffff1000101aadf4 x2 : 0000000000000001
[ 0.000000] x1 : 0000000000000001 x0 : 000000000000005d
[ 0.000000] Call trace:
[ 0.000000] early_init_on_free+0x1c0/0x200
[ 0.000000] do_early_param+0xd0/0x104
[ 0.000000] parse_args+0x1f0/0x524
[ 0.000000] parse_early_param+0x70/0x8c
[ 0.000000] setup_arch+0xa8/0x268
[ 0.000000] start_kernel+0x80/0x560
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