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[66.187.233.206]) by smtp.gmail.com with ESMTPSA id e125sm9726639qkd.120.2019.06.26.11.15.50 (version=TLS1_2 cipher=ECDHE-RSA-AES128-GCM-SHA256 bits=128/128); Wed, 26 Jun 2019 11:15:51 -0700 (PDT) Message-ID: <1561572949.5154.81.camel@lca.pw> Subject: Re: [PATCH v8 1/2] mm: security: introduce init_on_alloc=1 and init_on_free=1 boot options From: Qian Cai To: Alexander Potapenko , Andrew Morton , Christoph Lameter , Kees Cook Cc: Masahiro Yamada , Michal Hocko , James Morris , "Serge E. Hallyn" , Nick Desaulniers , Kostya Serebryany , Dmitry Vyukov , Sandeep Patil , Laura Abbott , Randy Dunlap , Jann Horn , Mark Rutland , Marco Elver , linux-mm@kvack.org, linux-security-module@vger.kernel.org, kernel-hardening@lists.openwall.com, clang-built-linux@googlegroups.com Date: Wed, 26 Jun 2019 14:15:49 -0400 In-Reply-To: <20190626121943.131390-2-glider@google.com> References: <20190626121943.131390-1-glider@google.com> <20190626121943.131390-2-glider@google.com> Content-Type: text/plain; charset="UTF-8" X-Mailer: Evolution 3.22.6 (3.22.6-10.el7) Mime-Version: 1.0 Content-Transfer-Encoding: 8bit X-Bogosity: Ham, tests=bogofilter, spamicity=0.000000, version=1.2.4 Sender: owner-linux-mm@kvack.org Precedence: bulk X-Loop: owner-majordomo@kvack.org List-ID: 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 > Acked-by: Kees Cook > To: Andrew Morton > To: Christoph Lameter > To: Kees Cook > Cc: Masahiro Yamada > Cc: Michal Hocko > Cc: James Morris > Cc: "Serge E. Hallyn" > Cc: Nick Desaulniers > Cc: Kostya Serebryany > Cc: Dmitry Vyukov > Cc: Sandeep Patil > Cc: Laura Abbott > Cc: Randy Dunlap > Cc: Jann Horn > Cc: Mark Rutland > Cc: Marco Elver > Cc: Qian Cai > Cc: linux-mm@kvack.org > Cc: linux-security-module@vger.kernel.org > Cc: kernel-hardening@lists.openwall.com > Signed-off-by: Andrew Morton > --- >  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