[PATCH v6 0/6] slab: Introduce dedicated bucket allocator

[PATCH v6 0/6] slab: Introduce dedicated bucket allocator

[Kees Cook]

Hi,

 v6:
  - update commit logs:
    - update description of Kconfig default and API details
    - call out usage of SLAB_NO_MERGE
    - improve description of cross-cache attacks
    - fix typos
  - add kern-doc parsing of DECL_BUCKET_PARAMS macro
  - add kern-doc to kmem_buckets_create()
  - have CONFIG_SLAB_BUCKETS default to CONFIG_SLAB_FREELIST_HARDENED
  - add CONFIG_SLAB_BUCKETS to hardening.config
  - drop alignment argument from kmem_buckets_create()
 v5: https://lore.kernel.org/lkml/20240619192131.do.115-kees@kernel.org
 v4: https://lore.kernel.org/lkml/20240531191304.it.853-kees@kernel.org/
 v3: https://lore.kernel.org/lkml/20240424213019.make.366-kees@kernel.org/
 v2: https://lore.kernel.org/lkml/20240305100933.it.923-kees@kernel.org/
 v1: https://lore.kernel.org/lkml/20240304184252.work.496-kees@kernel.org/

For the cover letter, I'm repeating the commit log for patch 4 here,
which has the more complete rationale:

    Dedicated caches are available for fixed size allocations via
    kmem_cache_alloc(), but for dynamically sized allocations there is only
    the global kmalloc API's set of buckets available. This means it isn't
    possible to separate specific sets of dynamically sized allocations into
    a separate collection of caches.

    This leads to a use-after-free exploitation weakness in the Linux
    kernel since many heap memory spraying/grooming attacks depend on using
    userspace-controllable dynamically sized allocations to collide with
    fixed size allocations that end up in same cache.

    While CONFIG_RANDOM_KMALLOC_CACHES provides a probabilistic defense
    against these kinds of "type confusion" attacks, including for fixed
    same-size heap objects, we can create a complementary deterministic
    defense for dynamically sized allocations that are directly user
    controlled. Addressing these cases is limited in scope, so isolating these
    kinds of interfaces will not become an unbounded game of whack-a-mole. For
    example, many pass through memdup_user(), making isolation there very
    effective.

    In order to isolate user-controllable dynamically-sized
    allocations from the common system kmalloc allocations, introduce
    kmem_buckets_create(), which behaves like kmem_cache_create(). Introduce
    kmem_buckets_alloc(), which behaves like kmem_cache_alloc(). Introduce
    kmem_buckets_alloc_track_caller() for where caller tracking is
    needed. Introduce kmem_buckets_valloc() for cases where vmalloc fallback
    is needed. Note that these caches are specifically flagged with
    SLAB_NO_MERGE, since merging would defeat the entire purpose of the
    mitigation.

    This can also be used in the future to extend allocation profiling's use
    of code tagging to implement per-caller allocation cache isolation[1]
    even for dynamic allocations.

    Memory allocation pinning[2] is still needed to plug the Use-After-Free
    cross-allocator weakness (where attackers can arrange to free an
    entire slab page and have it reallocated to a different cache),
    but that is an existing and separate issue which is complementary
    to this improvement. Development continues for that feature via the
    SLAB_VIRTUAL[3] series (which could also provide guard pages -- another
    complementary improvement).

    Link: https://lore.kernel.org/lkml/202402211449.401382D2AF@keescook [1]
    Link: https://googleprojectzero.blogspot.com/2021/10/how-simple-linux-kernel-memory.html [2]
    Link: https://lore.kernel.org/lkml/20230915105933.495735-1-matteorizzo@google.com/ [3]

After the core implementation are 2 patches that cover the most heavily
abused "repeat offenders" used in exploits. Repeating those details here:

    The msg subsystem is a common target for exploiting[1][2][3][4][5][6]
    use-after-free type confusion flaws in the kernel for both read and
    write primitives. Avoid having a user-controlled size cache share the
    global kmalloc allocator by using a separate set of kmalloc buckets.

    Link: https://blog.hacktivesecurity.com/index.php/2022/06/13/linux-kernel-exploit-development-1day-case-study/ [1]
    Link: https://hardenedvault.net/blog/2022-11-13-msg_msg-recon-mitigation-ved/ [2]
    Link: https://www.willsroot.io/2021/08/corctf-2021-fire-of-salvation-writeup.html [3]
    Link: https://a13xp0p0v.github.io/2021/02/09/CVE-2021-26708.html [4]
    Link: https://google.github.io/security-research/pocs/linux/cve-2021-22555/writeup.html [5]
    Link: https://zplin.me/papers/ELOISE.pdf [6]
    Link: https://syst3mfailure.io/wall-of-perdition/ [7]

    Both memdup_user() and vmemdup_user() handle allocations that are
    regularly used for exploiting use-after-free type confusion flaws in
    the kernel (e.g. prctl() PR_SET_VMA_ANON_NAME[1] and setxattr[2][3][4]
    respectively).

    Since both are designed for contents coming from userspace, it allows
    for userspace-controlled allocation sizes. Use a dedicated set of kmalloc
    buckets so these allocations do not share caches with the global kmalloc
    buckets.

    Link: https://starlabs.sg/blog/2023/07-prctl-anon_vma_name-an-amusing-heap-spray/ [1]
    Link: https://duasynt.com/blog/linux-kernel-heap-spray [2]
    Link: https://etenal.me/archives/1336 [3]
    Link: https://github.com/a13xp0p0v/kernel-hack-drill/blob/master/drill_exploit_uaf.c [4]

Thanks!

-Kees

Kees Cook (6):
  mm/slab: Introduce kmem_buckets typedef
  mm/slab: Plumb kmem_buckets into __do_kmalloc_node()
  mm/slab: Introduce kvmalloc_buckets_node() that can take kmem_buckets
    argument
  mm/slab: Introduce kmem_buckets_create() and family
  ipc, msg: Use dedicated slab buckets for alloc_msg()
  mm/util: Use dedicated slab buckets for memdup_user()

 include/linux/slab.h            |  48 ++++++++++++---
 ipc/msgutil.c                   |  13 +++-
 kernel/configs/hardening.config |   1 +
 mm/Kconfig                      |  17 ++++++
 mm/slab.h                       |   6 +-
 mm/slab_common.c                | 101 +++++++++++++++++++++++++++++++-
 mm/slub.c                       |  20 +++----
 mm/util.c                       |  23 ++++++--
 scripts/kernel-doc              |   1 +
 9 files changed, 200 insertions(+), 30 deletions(-)

-- 
2.34.1

[PATCH v6 1/6] mm/slab: Introduce kmem_buckets typedef

[Kees Cook]

Encapsulate the concept of a single set of kmem_caches that are used
for the kmalloc size buckets. Redefine kmalloc_caches as an array
of these buckets (for the different global cache buckets).

Signed-off-by: Kees Cook <kees@kernel.org>
---
 include/linux/slab.h | 5 +++--
 mm/slab_common.c     | 3 +--
 2 files changed, 4 insertions(+), 4 deletions(-)

diff --git a/include/linux/slab.h b/include/linux/slab.h
index ed6bee5ec2b6..8a006fac57c6 100644
--- a/include/linux/slab.h
+++ b/include/linux/slab.h
@@ -426,8 +426,9 @@ enum kmalloc_cache_type {
 	NR_KMALLOC_TYPES
 };
 
-extern struct kmem_cache *
-kmalloc_caches[NR_KMALLOC_TYPES][KMALLOC_SHIFT_HIGH + 1];
+typedef struct kmem_cache * kmem_buckets[KMALLOC_SHIFT_HIGH + 1];
+
+extern kmem_buckets kmalloc_caches[NR_KMALLOC_TYPES];
 
 /*
  * Define gfp bits that should not be set for KMALLOC_NORMAL.
diff --git a/mm/slab_common.c b/mm/slab_common.c
index 1560a1546bb1..e0b1c109bed2 100644
--- a/mm/slab_common.c
+++ b/mm/slab_common.c
@@ -653,8 +653,7 @@ static struct kmem_cache *__init create_kmalloc_cache(const char *name,
 	return s;
 }
 
-struct kmem_cache *
-kmalloc_caches[NR_KMALLOC_TYPES][KMALLOC_SHIFT_HIGH + 1] __ro_after_init =
+kmem_buckets kmalloc_caches[NR_KMALLOC_TYPES] __ro_after_init =
 { /* initialization for https://llvm.org/pr42570 */ };
 EXPORT_SYMBOL(kmalloc_caches);
 
-- 
2.34.1

[PATCH v6 2/6] mm/slab: Plumb kmem_buckets into __do_kmalloc_node()

[Kees Cook]

Introduce CONFIG_SLAB_BUCKETS which provides the infrastructure to
support separated kmalloc buckets (in the following kmem_buckets_create()
patches and future codetag-based separation). Since this will provide
a mitigation for a very common case of exploits, it is recommended to
enable this feature for general purpose distros. By default, the new
Kconfig will be enabled if CONFIG_SLAB_FREELIST_HARDENED is enabled (and
it is added to the hardening.config Kconfig fragment).

To be able to choose which buckets to allocate from, make the buckets
available to the internal kmalloc interfaces by adding them as the
second argument, rather than depending on the buckets being chosen from
the fixed set of global buckets. Where the bucket is not available,
pass NULL, which means "use the default system kmalloc bucket set"
(the prior existing behavior), as implemented in kmalloc_slab().

To avoid adding the extra argument when !CONFIG_SLAB_BUCKETS, only the
top-level macros and static inlines use the buckets argument (where
they are stripped out and compiled out respectively). The actual extern
functions can then be built without the argument, and the internals
fall back to the global kmalloc buckets unconditionally.

Co-developed-by: Vlastimil Babka <vbabka@suse.cz>
Signed-off-by: Vlastimil Babka <vbabka@suse.cz>
Signed-off-by: Kees Cook <kees@kernel.org>
---
 include/linux/slab.h            | 27 ++++++++++++++++++++++-----
 kernel/configs/hardening.config |  1 +
 mm/Kconfig                      | 17 +++++++++++++++++
 mm/slab.h                       |  6 ++++--
 mm/slab_common.c                |  2 +-
 mm/slub.c                       | 20 ++++++++++----------
 scripts/kernel-doc              |  1 +
 7 files changed, 56 insertions(+), 18 deletions(-)

diff --git a/include/linux/slab.h b/include/linux/slab.h
index 8a006fac57c6..708bde6039f0 100644
--- a/include/linux/slab.h
+++ b/include/linux/slab.h
@@ -570,6 +570,21 @@ void *kmem_cache_alloc_node_noprof(struct kmem_cache *s, gfp_t flags,
 				   int node) __assume_slab_alignment __malloc;
 #define kmem_cache_alloc_node(...)	alloc_hooks(kmem_cache_alloc_node_noprof(__VA_ARGS__))
 
+/*
+ * These macros allow declaring a kmem_buckets * parameter alongside size, which
+ * can be compiled out with CONFIG_SLAB_BUCKETS=n so that a large number of call
+ * sites don't have to pass NULL.
+ */
+#ifdef CONFIG_SLAB_BUCKETS
+#define DECL_BUCKET_PARAMS(_size, _b)	size_t (_size), kmem_buckets *(_b)
+#define PASS_BUCKET_PARAMS(_size, _b)	(_size), (_b)
+#define PASS_BUCKET_PARAM(_b)		(_b)
+#else
+#define DECL_BUCKET_PARAMS(_size, _b)	size_t (_size)
+#define PASS_BUCKET_PARAMS(_size, _b)	(_size)
+#define PASS_BUCKET_PARAM(_b)		NULL
+#endif
+
 /*
  * The following functions are not to be used directly and are intended only
  * for internal use from kmalloc() and kmalloc_node()
@@ -579,7 +594,7 @@ void *kmem_cache_alloc_node_noprof(struct kmem_cache *s, gfp_t flags,
 void *__kmalloc_noprof(size_t size, gfp_t flags)
 				__assume_kmalloc_alignment __alloc_size(1);
 
-void *__kmalloc_node_noprof(size_t size, gfp_t flags, int node)
+void *__kmalloc_node_noprof(DECL_BUCKET_PARAMS(size, b), gfp_t flags, int node)
 				__assume_kmalloc_alignment __alloc_size(1);
 
 void *__kmalloc_cache_noprof(struct kmem_cache *s, gfp_t flags, size_t size)
@@ -679,7 +694,7 @@ static __always_inline __alloc_size(1) void *kmalloc_node_noprof(size_t size, gf
 				kmalloc_caches[kmalloc_type(flags, _RET_IP_)][index],
 				flags, node, size);
 	}
-	return __kmalloc_node_noprof(size, flags, node);
+	return __kmalloc_node_noprof(PASS_BUCKET_PARAMS(size, NULL), flags, node);
 }
 #define kmalloc_node(...)			alloc_hooks(kmalloc_node_noprof(__VA_ARGS__))
 
@@ -730,8 +745,10 @@ static inline __realloc_size(2, 3) void * __must_check krealloc_array_noprof(voi
  */
 #define kcalloc(n, size, flags)		kmalloc_array(n, size, (flags) | __GFP_ZERO)
 
-void *kmalloc_node_track_caller_noprof(size_t size, gfp_t flags, int node,
-				  unsigned long caller) __alloc_size(1);
+void *__kmalloc_node_track_caller_noprof(DECL_BUCKET_PARAMS(size, b), gfp_t flags, int node,
+					 unsigned long caller) __alloc_size(1);
+#define kmalloc_node_track_caller_noprof(size, flags, node, caller) \
+	__kmalloc_node_track_caller_noprof(PASS_BUCKET_PARAMS(size, NULL), flags, node, caller)
 #define kmalloc_node_track_caller(...)		\
 	alloc_hooks(kmalloc_node_track_caller_noprof(__VA_ARGS__, _RET_IP_))
 
@@ -757,7 +774,7 @@ static inline __alloc_size(1, 2) void *kmalloc_array_node_noprof(size_t n, size_
 		return NULL;
 	if (__builtin_constant_p(n) && __builtin_constant_p(size))
 		return kmalloc_node_noprof(bytes, flags, node);
-	return __kmalloc_node_noprof(bytes, flags, node);
+	return __kmalloc_node_noprof(PASS_BUCKET_PARAMS(bytes, NULL), flags, node);
 }
 #define kmalloc_array_node(...)			alloc_hooks(kmalloc_array_node_noprof(__VA_ARGS__))
 
diff --git a/kernel/configs/hardening.config b/kernel/configs/hardening.config
index 8a7ce7a6b3ab..3fabb8f55ef6 100644
--- a/kernel/configs/hardening.config
+++ b/kernel/configs/hardening.config
@@ -20,6 +20,7 @@ CONFIG_RANDOMIZE_MEMORY=y
 # Randomize allocator freelists, harden metadata.
 CONFIG_SLAB_FREELIST_RANDOM=y
 CONFIG_SLAB_FREELIST_HARDENED=y
+CONFIG_SLAB_BUCKETS=y
 CONFIG_SHUFFLE_PAGE_ALLOCATOR=y
 CONFIG_RANDOM_KMALLOC_CACHES=y
 
diff --git a/mm/Kconfig b/mm/Kconfig
index b4cb45255a54..e0dfb268717c 100644
--- a/mm/Kconfig
+++ b/mm/Kconfig
@@ -273,6 +273,23 @@ config SLAB_FREELIST_HARDENED
 	  sacrifices to harden the kernel slab allocator against common
 	  freelist exploit methods.
 
+config SLAB_BUCKETS
+	bool "Support allocation from separate kmalloc buckets"
+	depends on !SLUB_TINY
+	default SLAB_FREELIST_HARDENED
+	help
+	  Kernel heap attacks frequently depend on being able to create
+	  specifically-sized allocations with user-controlled contents
+	  that will be allocated into the same kmalloc bucket as a
+	  target object. To avoid sharing these allocation buckets,
+	  provide an explicitly separated set of buckets to be used for
+	  user-controlled allocations. This may very slightly increase
+	  memory fragmentation, though in practice it's only a handful
+	  of extra pages since the bulk of user-controlled allocations
+	  are relatively long-lived.
+
+	  If unsure, say Y.
+
 config SLUB_STATS
 	default n
 	bool "Enable performance statistics"
diff --git a/mm/slab.h b/mm/slab.h
index b16e63191578..d5e8034af9d5 100644
--- a/mm/slab.h
+++ b/mm/slab.h
@@ -403,16 +403,18 @@ static inline unsigned int size_index_elem(unsigned int bytes)
  * KMALLOC_MAX_CACHE_SIZE and the caller must check that.
  */
 static inline struct kmem_cache *
-kmalloc_slab(size_t size, gfp_t flags, unsigned long caller)
+kmalloc_slab(size_t size, kmem_buckets *b, gfp_t flags, unsigned long caller)
 {
 	unsigned int index;
 
+	if (!b)
+		b = &kmalloc_caches[kmalloc_type(flags, caller)];
 	if (size <= 192)
 		index = kmalloc_size_index[size_index_elem(size)];
 	else
 		index = fls(size - 1);
 
-	return kmalloc_caches[kmalloc_type(flags, caller)][index];
+	return (*b)[index];
 }
 
 gfp_t kmalloc_fix_flags(gfp_t flags);
diff --git a/mm/slab_common.c b/mm/slab_common.c
index e0b1c109bed2..9b0f2ef951f1 100644
--- a/mm/slab_common.c
+++ b/mm/slab_common.c
@@ -702,7 +702,7 @@ size_t kmalloc_size_roundup(size_t size)
 		 * The flags don't matter since size_index is common to all.
 		 * Neither does the caller for just getting ->object_size.
 		 */
-		return kmalloc_slab(size, GFP_KERNEL, 0)->object_size;
+		return kmalloc_slab(size, NULL, GFP_KERNEL, 0)->object_size;
 	}
 
 	/* Above the smaller buckets, size is a multiple of page size. */
diff --git a/mm/slub.c b/mm/slub.c
index 3d19a0ee411f..80f0a51242d1 100644
--- a/mm/slub.c
+++ b/mm/slub.c
@@ -4117,7 +4117,7 @@ void *__kmalloc_large_node_noprof(size_t size, gfp_t flags, int node)
 EXPORT_SYMBOL(__kmalloc_large_node_noprof);
 
 static __always_inline
-void *__do_kmalloc_node(size_t size, gfp_t flags, int node,
+void *__do_kmalloc_node(size_t size, kmem_buckets *b, gfp_t flags, int node,
 			unsigned long caller)
 {
 	struct kmem_cache *s;
@@ -4133,32 +4133,32 @@ void *__do_kmalloc_node(size_t size, gfp_t flags, int node,
 	if (unlikely(!size))
 		return ZERO_SIZE_PTR;
 
-	s = kmalloc_slab(size, flags, caller);
+	s = kmalloc_slab(size, b, flags, caller);
 
 	ret = slab_alloc_node(s, NULL, flags, node, caller, size);
 	ret = kasan_kmalloc(s, ret, size, flags);
 	trace_kmalloc(caller, ret, size, s->size, flags, node);
 	return ret;
 }
-
-void *__kmalloc_node_noprof(size_t size, gfp_t flags, int node)
+void *__kmalloc_node_noprof(DECL_BUCKET_PARAMS(size, b), gfp_t flags, int node)
 {
-	return __do_kmalloc_node(size, flags, node, _RET_IP_);
+	return __do_kmalloc_node(size, PASS_BUCKET_PARAM(b), flags, node, _RET_IP_);
 }
 EXPORT_SYMBOL(__kmalloc_node_noprof);
 
 void *__kmalloc_noprof(size_t size, gfp_t flags)
 {
-	return __do_kmalloc_node(size, flags, NUMA_NO_NODE, _RET_IP_);
+	return __do_kmalloc_node(size, NULL, flags, NUMA_NO_NODE, _RET_IP_);
 }
 EXPORT_SYMBOL(__kmalloc_noprof);
 
-void *kmalloc_node_track_caller_noprof(size_t size, gfp_t flags,
-				       int node, unsigned long caller)
+void *__kmalloc_node_track_caller_noprof(DECL_BUCKET_PARAMS(size, b), gfp_t flags,
+					 int node, unsigned long caller)
 {
-	return __do_kmalloc_node(size, flags, node, caller);
+	return __do_kmalloc_node(size, PASS_BUCKET_PARAM(b), flags, node, caller);
+
 }
-EXPORT_SYMBOL(kmalloc_node_track_caller_noprof);
+EXPORT_SYMBOL(__kmalloc_node_track_caller_noprof);
 
 void *__kmalloc_cache_noprof(struct kmem_cache *s, gfp_t gfpflags, size_t size)
 {
diff --git a/scripts/kernel-doc b/scripts/kernel-doc
index 95a59ac78f82..2791f8195203 100755
--- a/scripts/kernel-doc
+++ b/scripts/kernel-doc
@@ -1729,6 +1729,7 @@ sub dump_function($$) {
     $prototype =~ s/__printf\s*\(\s*\d*\s*,\s*\d*\s*\) +//;
     $prototype =~ s/__(?:re)?alloc_size\s*\(\s*\d+\s*(?:,\s*\d+\s*)?\) +//;
     $prototype =~ s/__diagnose_as\s*\(\s*\S+\s*(?:,\s*\d+\s*)*\) +//;
+    $prototype =~ s/DECL_BUCKET_PARAMS\s*\(\s*(\S+)\s*,\s*(\S+)\s*\)/$1, $2/;
     my $define = $prototype =~ s/^#\s*define\s+//; #ak added
     $prototype =~ s/__attribute_const__ +//;
     $prototype =~ s/__attribute__\s*\(\(
-- 
2.34.1

[PATCH v6 3/6] mm/slab: Introduce kvmalloc_buckets_node() that can take kmem_buckets argument

[Kees Cook]

Plumb kmem_buckets arguments through kvmalloc_node_noprof() so it is
possible to provide an API to perform kvmalloc-style allocations with
a particular set of buckets. Introduce kvmalloc_buckets_node() that takes a
kmem_buckets argument.

Signed-off-by: Kees Cook <kees@kernel.org>
---
 include/linux/slab.h | 4 +++-
 mm/util.c            | 9 +++++----
 2 files changed, 8 insertions(+), 5 deletions(-)

diff --git a/include/linux/slab.h b/include/linux/slab.h
index 708bde6039f0..8d0800c7579a 100644
--- a/include/linux/slab.h
+++ b/include/linux/slab.h
@@ -798,7 +798,9 @@ static inline __alloc_size(1) void *kzalloc_noprof(size_t size, gfp_t flags)
 #define kzalloc(...)				alloc_hooks(kzalloc_noprof(__VA_ARGS__))
 #define kzalloc_node(_size, _flags, _node)	kmalloc_node(_size, (_flags)|__GFP_ZERO, _node)
 
-extern void *kvmalloc_node_noprof(size_t size, gfp_t flags, int node) __alloc_size(1);
+void *__kvmalloc_node_noprof(DECL_BUCKET_PARAMS(size, b), gfp_t flags, int node) __alloc_size(1);
+#define kvmalloc_node_noprof(size, flags, node)	\
+	__kvmalloc_node_noprof(PASS_BUCKET_PARAMS(size, NULL), flags, node)
 #define kvmalloc_node(...)			alloc_hooks(kvmalloc_node_noprof(__VA_ARGS__))
 
 #define kvmalloc(_size, _flags)			kvmalloc_node(_size, _flags, NUMA_NO_NODE)
diff --git a/mm/util.c b/mm/util.c
index c9e519e6811f..28c5356b9f1c 100644
--- a/mm/util.c
+++ b/mm/util.c
@@ -594,9 +594,10 @@ unsigned long vm_mmap(struct file *file, unsigned long addr,
 EXPORT_SYMBOL(vm_mmap);
 
 /**
- * kvmalloc_node - attempt to allocate physically contiguous memory, but upon
+ * __kvmalloc_node - attempt to allocate physically contiguous memory, but upon
  * failure, fall back to non-contiguous (vmalloc) allocation.
  * @size: size of the request.
+ * @b: which set of kmalloc buckets to allocate from.
  * @flags: gfp mask for the allocation - must be compatible (superset) with GFP_KERNEL.
  * @node: numa node to allocate from
  *
@@ -609,7 +610,7 @@ EXPORT_SYMBOL(vm_mmap);
  *
  * Return: pointer to the allocated memory of %NULL in case of failure
  */
-void *kvmalloc_node_noprof(size_t size, gfp_t flags, int node)
+void *__kvmalloc_node_noprof(DECL_BUCKET_PARAMS(size, b), gfp_t flags, int node)
 {
 	gfp_t kmalloc_flags = flags;
 	void *ret;
@@ -631,7 +632,7 @@ void *kvmalloc_node_noprof(size_t size, gfp_t flags, int node)
 		kmalloc_flags &= ~__GFP_NOFAIL;
 	}
 
-	ret = kmalloc_node_noprof(size, kmalloc_flags, node);
+	ret = __kmalloc_node_noprof(PASS_BUCKET_PARAMS(size, b), kmalloc_flags, node);
 
 	/*
 	 * It doesn't really make sense to fallback to vmalloc for sub page
@@ -660,7 +661,7 @@ void *kvmalloc_node_noprof(size_t size, gfp_t flags, int node)
 			flags, PAGE_KERNEL, VM_ALLOW_HUGE_VMAP,
 			node, __builtin_return_address(0));
 }
-EXPORT_SYMBOL(kvmalloc_node_noprof);
+EXPORT_SYMBOL(__kvmalloc_node_noprof);
 
 /**
  * kvfree() - Free memory.
-- 
2.34.1

[PATCH v6 4/6] mm/slab: Introduce kmem_buckets_create() and family

[Kees Cook]

Dedicated caches are available for fixed size allocations via
kmem_cache_alloc(), but for dynamically sized allocations there is only
the global kmalloc API's set of buckets available. This means it isn't
possible to separate specific sets of dynamically sized allocations into
a separate collection of caches.

This leads to a use-after-free exploitation weakness in the Linux
kernel since many heap memory spraying/grooming attacks depend on using
userspace-controllable dynamically sized allocations to collide with
fixed size allocations that end up in same cache.

While CONFIG_RANDOM_KMALLOC_CACHES provides a probabilistic defense
against these kinds of "type confusion" attacks, including for fixed
same-size heap objects, we can create a complementary deterministic
defense for dynamically sized allocations that are directly user
controlled. Addressing these cases is limited in scope, so isolating these
kinds of interfaces will not become an unbounded game of whack-a-mole. For
example, many pass through memdup_user(), making isolation there very
effective.

In order to isolate user-controllable dynamically-sized
allocations from the common system kmalloc allocations, introduce
kmem_buckets_create(), which behaves like kmem_cache_create(). Introduce
kmem_buckets_alloc(), which behaves like kmem_cache_alloc(). Introduce
kmem_buckets_alloc_track_caller() for where caller tracking is
needed. Introduce kmem_buckets_valloc() for cases where vmalloc fallback
is needed. Note that these caches are specifically flagged with
SLAB_NO_MERGE, since merging would defeat the entire purpose of the
mitigation.

This can also be used in the future to extend allocation profiling's use
of code tagging to implement per-caller allocation cache isolation[1]
even for dynamic allocations.

Memory allocation pinning[2] is still needed to plug the Use-After-Free
cross-allocator weakness (where attackers can arrange to free an
entire slab page and have it reallocated to a different cache),
but that is an existing and separate issue which is complementary
to this improvement. Development continues for that feature via the
SLAB_VIRTUAL[3] series (which could also provide guard pages -- another
complementary improvement).

Link: https://lore.kernel.org/lkml/202402211449.401382D2AF@keescook [1]
Link: https://googleprojectzero.blogspot.com/2021/10/how-simple-linux-kernel-memory.html [2]
Link: https://lore.kernel.org/lkml/20230915105933.495735-1-matteorizzo@google.com/ [3]
Signed-off-by: Kees Cook <kees@kernel.org>
---
 include/linux/slab.h | 12 ++++++
 mm/slab_common.c     | 96 ++++++++++++++++++++++++++++++++++++++++++++
 2 files changed, 108 insertions(+)

diff --git a/include/linux/slab.h b/include/linux/slab.h
index 8d0800c7579a..4c083f3196f4 100644
--- a/include/linux/slab.h
+++ b/include/linux/slab.h
@@ -549,6 +549,10 @@ void *kmem_cache_alloc_lru_noprof(struct kmem_cache *s, struct list_lru *lru,
 
 void kmem_cache_free(struct kmem_cache *s, void *objp);
 
+kmem_buckets *kmem_buckets_create(const char *name, slab_flags_t flags,
+				  unsigned int useroffset, unsigned int usersize,
+				  void (*ctor)(void *));
+
 /*
  * Bulk allocation and freeing operations. These are accelerated in an
  * allocator specific way to avoid taking locks repeatedly or building
@@ -681,6 +685,12 @@ static __always_inline __alloc_size(1) void *kmalloc_noprof(size_t size, gfp_t f
 }
 #define kmalloc(...)				alloc_hooks(kmalloc_noprof(__VA_ARGS__))
 
+#define kmem_buckets_alloc(_b, _size, _flags)	\
+	alloc_hooks(__kmalloc_node_noprof(PASS_BUCKET_PARAMS(_size, _b), _flags, NUMA_NO_NODE))
+
+#define kmem_buckets_alloc_track_caller(_b, _size, _flags)	\
+	alloc_hooks(__kmalloc_node_track_caller_noprof(PASS_BUCKET_PARAMS(_size, _b), _flags, NUMA_NO_NODE, _RET_IP_))
+
 static __always_inline __alloc_size(1) void *kmalloc_node_noprof(size_t size, gfp_t flags, int node)
 {
 	if (__builtin_constant_p(size) && size) {
@@ -808,6 +818,8 @@ void *__kvmalloc_node_noprof(DECL_BUCKET_PARAMS(size, b), gfp_t flags, int node)
 #define kvzalloc(_size, _flags)			kvmalloc(_size, (_flags)|__GFP_ZERO)
 
 #define kvzalloc_node(_size, _flags, _node)	kvmalloc_node(_size, (_flags)|__GFP_ZERO, _node)
+#define kmem_buckets_valloc(_b, _size, _flags)	\
+	alloc_hooks(__kvmalloc_node_noprof(PASS_BUCKET_PARAMS(_size, _b), _flags, NUMA_NO_NODE))
 
 static inline __alloc_size(1, 2) void *
 kvmalloc_array_node_noprof(size_t n, size_t size, gfp_t flags, int node)
diff --git a/mm/slab_common.c b/mm/slab_common.c
index 9b0f2ef951f1..641cf513d2d1 100644
--- a/mm/slab_common.c
+++ b/mm/slab_common.c
@@ -392,6 +392,98 @@ kmem_cache_create(const char *name, unsigned int size, unsigned int align,
 }
 EXPORT_SYMBOL(kmem_cache_create);
 
+static struct kmem_cache *kmem_buckets_cache __ro_after_init;
+
+/**
+ * kmem_buckets_create - Create a set of caches that handle dynamic sized
+ *			 allocations via kmem_buckets_alloc()
+ * @name: A prefix string which is used in /proc/slabinfo to identify this
+ *	  cache. The individual caches with have their sizes as the suffix.
+ * @flags: SLAB flags (see kmem_cache_create() for details).
+ * @useroffset: Starting offset within an allocation that may be copied
+ *		to/from userspace.
+ * @usersize: How many bytes, starting at @useroffset, may be copied
+ *		to/from userspace.
+ * @ctor: A constructor for the objects, run when new allocations are made.
+ *
+ * Cannot be called within an interrupt, but can be interrupted.
+ *
+ * Return: a pointer to the cache on success, NULL on failure. When
+ * CONFIG_SLAB_BUCKETS is not enabled, ZERO_SIZE_PTR is returned, and
+ * subsequent calls to kmem_buckets_alloc() will fall back to kmalloc().
+ * (i.e. callers only need to check for NULL on failure.)
+ */
+kmem_buckets *kmem_buckets_create(const char *name, slab_flags_t flags,
+				  unsigned int useroffset,
+				  unsigned int usersize,
+				  void (*ctor)(void *))
+{
+	kmem_buckets *b;
+	int idx;
+
+	/*
+	 * When the separate buckets API is not built in, just return
+	 * a non-NULL value for the kmem_buckets pointer, which will be
+	 * unused when performing allocations.
+	 */
+	if (!IS_ENABLED(CONFIG_SLAB_BUCKETS))
+		return ZERO_SIZE_PTR;
+
+	if (WARN_ON(!kmem_buckets_cache))
+		return NULL;
+
+	b = kmem_cache_alloc(kmem_buckets_cache, GFP_KERNEL|__GFP_ZERO);
+	if (WARN_ON(!b))
+		return NULL;
+
+	flags |= SLAB_NO_MERGE;
+
+	for (idx = 0; idx < ARRAY_SIZE(kmalloc_caches[KMALLOC_NORMAL]); idx++) {
+		char *short_size, *cache_name;
+		unsigned int cache_useroffset, cache_usersize;
+		unsigned int size;
+
+		if (!kmalloc_caches[KMALLOC_NORMAL][idx])
+			continue;
+
+		size = kmalloc_caches[KMALLOC_NORMAL][idx]->object_size;
+		if (!size)
+			continue;
+
+		short_size = strchr(kmalloc_caches[KMALLOC_NORMAL][idx]->name, '-');
+		if (WARN_ON(!short_size))
+			goto fail;
+
+		cache_name = kasprintf(GFP_KERNEL, "%s-%s", name, short_size + 1);
+		if (WARN_ON(!cache_name))
+			goto fail;
+
+		if (useroffset >= size) {
+			cache_useroffset = 0;
+			cache_usersize = 0;
+		} else {
+			cache_useroffset = useroffset;
+			cache_usersize = min(size - cache_useroffset, usersize);
+		}
+		(*b)[idx] = kmem_cache_create_usercopy(cache_name, size,
+					0, flags, cache_useroffset,
+					cache_usersize, ctor);
+		kfree(cache_name);
+		if (WARN_ON(!(*b)[idx]))
+			goto fail;
+	}
+
+	return b;
+
+fail:
+	for (idx = 0; idx < ARRAY_SIZE(kmalloc_caches[KMALLOC_NORMAL]); idx++)
+		kmem_cache_destroy((*b)[idx]);
+	kfree(b);
+
+	return NULL;
+}
+EXPORT_SYMBOL(kmem_buckets_create);
+
 #ifdef SLAB_SUPPORTS_SYSFS
 /*
  * For a given kmem_cache, kmem_cache_destroy() should only be called
@@ -931,6 +1023,10 @@ void __init create_kmalloc_caches(void)
 
 	/* Kmalloc array is now usable */
 	slab_state = UP;
+
+	kmem_buckets_cache = kmem_cache_create("kmalloc_buckets",
+					       sizeof(kmem_buckets),
+					       0, SLAB_NO_MERGE, NULL);
 }
 
 /**
-- 
2.34.1

[PATCH v6 5/6] ipc, msg: Use dedicated slab buckets for alloc_msg()

[Kees Cook]

The msg subsystem is a common target for exploiting[1][2][3][4][5][6][7]
use-after-free type confusion flaws in the kernel for both read and write
primitives. Avoid having a user-controlled dynamically-size allocation
share the global kmalloc cache by using a separate set of kmalloc buckets
via the kmem_buckets API.

Link: https://blog.hacktivesecurity.com/index.php/2022/06/13/linux-kernel-exploit-development-1day-case-study/ [1]
Link: https://hardenedvault.net/blog/2022-11-13-msg_msg-recon-mitigation-ved/ [2]
Link: https://www.willsroot.io/2021/08/corctf-2021-fire-of-salvation-writeup.html [3]
Link: https://a13xp0p0v.github.io/2021/02/09/CVE-2021-26708.html [4]
Link: https://google.github.io/security-research/pocs/linux/cve-2021-22555/writeup.html [5]
Link: https://zplin.me/papers/ELOISE.pdf [6]
Link: https://syst3mfailure.io/wall-of-perdition/ [7]
Signed-off-by: Kees Cook <kees@kernel.org>
---
 ipc/msgutil.c | 13 ++++++++++++-
 1 file changed, 12 insertions(+), 1 deletion(-)

diff --git a/ipc/msgutil.c b/ipc/msgutil.c
index d0a0e877cadd..c7be0c792647 100644
--- a/ipc/msgutil.c
+++ b/ipc/msgutil.c
@@ -42,6 +42,17 @@ struct msg_msgseg {
 #define DATALEN_MSG	((size_t)PAGE_SIZE-sizeof(struct msg_msg))
 #define DATALEN_SEG	((size_t)PAGE_SIZE-sizeof(struct msg_msgseg))
 
+static kmem_buckets *msg_buckets __ro_after_init;
+
+static int __init init_msg_buckets(void)
+{
+	msg_buckets = kmem_buckets_create("msg_msg", SLAB_ACCOUNT,
+					  sizeof(struct msg_msg),
+					  DATALEN_MSG, NULL);
+
+	return 0;
+}
+subsys_initcall(init_msg_buckets);
 
 static struct msg_msg *alloc_msg(size_t len)
 {
@@ -50,7 +61,7 @@ static struct msg_msg *alloc_msg(size_t len)
 	size_t alen;
 
 	alen = min(len, DATALEN_MSG);
-	msg = kmalloc(sizeof(*msg) + alen, GFP_KERNEL_ACCOUNT);
+	msg = kmem_buckets_alloc(msg_buckets, sizeof(*msg) + alen, GFP_KERNEL);
 	if (msg == NULL)
 		return NULL;
 
-- 
2.34.1

[PATCH v6 6/6] mm/util: Use dedicated slab buckets for memdup_user()

[Kees Cook]

Both memdup_user() and vmemdup_user() handle allocations that are
regularly used for exploiting use-after-free type confusion flaws in
the kernel (e.g. prctl() PR_SET_VMA_ANON_NAME[1] and setxattr[2][3][4]
respectively).

Since both are designed for contents coming from userspace, it allows
for userspace-controlled allocation sizes. Use a dedicated set of kmalloc
buckets so these allocations do not share caches with the global kmalloc
buckets.

After a fresh boot under Ubuntu 23.10, we can see the caches are already
in active use:

 # grep ^memdup /proc/slabinfo
 memdup_user-8k         4      4   8192    4    8 : ...
 memdup_user-4k         8      8   4096    8    8 : ...
 memdup_user-2k        16     16   2048   16    8 : ...
 memdup_user-1k         0      0   1024   16    4 : ...
 memdup_user-512        0      0    512   16    2 : ...
 memdup_user-256        0      0    256   16    1 : ...
 memdup_user-128        0      0    128   32    1 : ...
 memdup_user-64       256    256     64   64    1 : ...
 memdup_user-32       512    512     32  128    1 : ...
 memdup_user-16      1024   1024     16  256    1 : ...
 memdup_user-8       2048   2048      8  512    1 : ...
 memdup_user-192        0      0    192   21    1 : ...
 memdup_user-96       168    168     96   42    1 : ...

Link: https://starlabs.sg/blog/2023/07-prctl-anon_vma_name-an-amusing-heap-spray/ [1]
Link: https://duasynt.com/blog/linux-kernel-heap-spray [2]
Link: https://etenal.me/archives/1336 [3]
Link: https://github.com/a13xp0p0v/kernel-hack-drill/blob/master/drill_exploit_uaf.c [4]
Signed-off-by: Kees Cook <kees@kernel.org>
---
 mm/util.c | 14 ++++++++++++--
 1 file changed, 12 insertions(+), 2 deletions(-)

diff --git a/mm/util.c b/mm/util.c
index 28c5356b9f1c..29189f48ee04 100644
--- a/mm/util.c
+++ b/mm/util.c
@@ -198,6 +198,16 @@ char *kmemdup_nul(const char *s, size_t len, gfp_t gfp)
 }
 EXPORT_SYMBOL(kmemdup_nul);
 
+static kmem_buckets *user_buckets __ro_after_init;
+
+static int __init init_user_buckets(void)
+{
+	user_buckets = kmem_buckets_create("memdup_user", 0, 0, INT_MAX, NULL);
+
+	return 0;
+}
+subsys_initcall(init_user_buckets);
+
 /**
  * memdup_user - duplicate memory region from user space
  *
@@ -211,7 +221,7 @@ void *memdup_user(const void __user *src, size_t len)
 {
 	void *p;
 
-	p = kmalloc_track_caller(len, GFP_USER | __GFP_NOWARN);
+	p = kmem_buckets_alloc_track_caller(user_buckets, len, GFP_USER | __GFP_NOWARN);
 	if (!p)
 		return ERR_PTR(-ENOMEM);
 
@@ -237,7 +247,7 @@ void *vmemdup_user(const void __user *src, size_t len)
 {
 	void *p;
 
-	p = kvmalloc(len, GFP_USER);
+	p = kmem_buckets_valloc(user_buckets, len, GFP_USER);
 	if (!p)
 		return ERR_PTR(-ENOMEM);
 
-- 
2.34.1

Re: [PATCH v6 4/6] mm/slab: Introduce kmem_buckets_create() and family

[Vlastimil Babka]

On 7/1/24 9:13 PM, Kees Cook wrote:
>  #ifdef SLAB_SUPPORTS_SYSFS
>  /*
>   * For a given kmem_cache, kmem_cache_destroy() should only be called
> @@ -931,6 +1023,10 @@ void __init create_kmalloc_caches(void)
>  
>  	/* Kmalloc array is now usable */
>  	slab_state = UP;
> +
> +	kmem_buckets_cache = kmem_cache_create("kmalloc_buckets",
> +					       sizeof(kmem_buckets),
> +					       0, SLAB_NO_MERGE, NULL);

Locally adjusted to put this behind "if (IS_ENABLED(CONFIG_SLAB_BUCKETS))"

>  }
>  
>  /**

Re: [PATCH v6 0/6] slab: Introduce dedicated bucket allocator

[Vlastimil Babka]

On 7/1/24 9:12 PM, Kees Cook wrote:
> 
> Kees Cook (6):
>   mm/slab: Introduce kmem_buckets typedef
>   mm/slab: Plumb kmem_buckets into __do_kmalloc_node()
>   mm/slab: Introduce kvmalloc_buckets_node() that can take kmem_buckets
>     argument
>   mm/slab: Introduce kmem_buckets_create() and family
>   ipc, msg: Use dedicated slab buckets for alloc_msg()
>   mm/util: Use dedicated slab buckets for memdup_user()

pushed to slab/for-6.11/buckets, slab/for-next

Thanks!

> 
>  include/linux/slab.h            |  48 ++++++++++++---
>  ipc/msgutil.c                   |  13 +++-
>  kernel/configs/hardening.config |   1 +
>  mm/Kconfig                      |  17 ++++++
>  mm/slab.h                       |   6 +-
>  mm/slab_common.c                | 101 +++++++++++++++++++++++++++++++-
>  mm/slub.c                       |  20 +++----
>  mm/util.c                       |  23 ++++++--
>  scripts/kernel-doc              |   1 +
>  9 files changed, 200 insertions(+), 30 deletions(-)
> 

Re: [PATCH v6 4/6] mm/slab: Introduce kmem_buckets_create() and family

[Kees Cook]

On Tue, Jul 02, 2024 at 11:19:28AM +0200, Vlastimil Babka wrote:
> On 7/1/24 9:13 PM, Kees Cook wrote:
> >  #ifdef SLAB_SUPPORTS_SYSFS
> >  /*
> >   * For a given kmem_cache, kmem_cache_destroy() should only be called
> > @@ -931,6 +1023,10 @@ void __init create_kmalloc_caches(void)
> >  
> >  	/* Kmalloc array is now usable */
> >  	slab_state = UP;
> > +
> > +	kmem_buckets_cache = kmem_cache_create("kmalloc_buckets",
> > +					       sizeof(kmem_buckets),
> > +					       0, SLAB_NO_MERGE, NULL);
> 
> Locally adjusted to put this behind "if (IS_ENABLED(CONFIG_SLAB_BUCKETS))"

Oops, yes, good catch. Thank you!

-- 
Kees Cook

Re: [PATCH v6 0/6] slab: Introduce dedicated bucket allocator

[Kees Cook]

On Tue, Jul 02, 2024 at 11:24:57AM +0200, Vlastimil Babka wrote:
> On 7/1/24 9:12 PM, Kees Cook wrote:
> > 
> > Kees Cook (6):
> >   mm/slab: Introduce kmem_buckets typedef
> >   mm/slab: Plumb kmem_buckets into __do_kmalloc_node()
> >   mm/slab: Introduce kvmalloc_buckets_node() that can take kmem_buckets
> >     argument
> >   mm/slab: Introduce kmem_buckets_create() and family
> >   ipc, msg: Use dedicated slab buckets for alloc_msg()
> >   mm/util: Use dedicated slab buckets for memdup_user()
> 
> pushed to slab/for-6.11/buckets, slab/for-next

Great! Thanks for the review and improvements! :) I'll get started on
the next step getting it hooked up to the codetag bits...

-- 
Kees Cook