This patch-set introduces the possibility of protecting memory that has
been allocated dynamically.
The memory is managed in pools: when a memory pool is protected, all the
memory that is currently part of it, will become R/O.
A R/O pool can be expanded (adding more protectable memory).
It can also be destroyed, to recover its memory, but it cannot be
turned back into R/W mode.
This is intentional. This feature is meant for data that doesn't need
further modifications after initialization.
However the data might need to be released, for example as part of module
unloading. The pool, therefore, can be destroyed.
An example is provided, in the form of self-testing.
Changes since v20:
[http://www.openwall.com/lists/kernel-hardening/2018/03/27/2]
* removed the align_order parameter from allocation functions
* improved documentation with more explanation
* fixed lkdt test
* reworked the destroy function, removing a possible race with
use-after-free code.
Igor Stoppa (6):
struct page: add field for vm_struct
vmalloc: rename llist field in vmap_area
Protectable Memory
Pmalloc selftest
lkdtm: crash on overwriting protected pmalloc var
Documentation for Pmalloc
Documentation/core-api/index.rst | 1 +
Documentation/core-api/pmalloc.rst | 107 +++++++++++++++
drivers/misc/lkdtm.h | 1 +
drivers/misc/lkdtm_core.c | 3 +
drivers/misc/lkdtm_perms.c | 25 ++++
include/linux/mm_types.h | 1 +
include/linux/pmalloc.h | 166 +++++++++++++++++++++++
include/linux/test_pmalloc.h | 24 ++++
include/linux/vmalloc.h | 5 +-
init/main.c | 2 +
mm/Kconfig | 16 +++
mm/Makefile | 2 +
mm/pmalloc.c | 264 +++++++++++++++++++++++++++++++++++++
mm/test_pmalloc.c | 136 +++++++++++++++++++
mm/usercopy.c | 33 +++++
mm/vmalloc.c | 10 +-
16 files changed, 791 insertions(+), 5 deletions(-)
create mode 100644 Documentation/core-api/pmalloc.rst
create mode 100644 include/linux/pmalloc.h
create mode 100644 include/linux/test_pmalloc.h
create mode 100644 mm/pmalloc.c
create mode 100644 mm/test_pmalloc.c
--
2.14.1
When a page is used for virtual memory, it is often necessary to obtain
a handler to the corresponding vm_struct, which refers to the virtually
continuous area generated when invoking vmalloc.
The struct page has a "mapping" field, which can be re-used, to store a
pointer to the parent area.
This will avoid more expensive searches, later on.
Signed-off-by: Igor Stoppa <[email protected]>
Reviewed-by: Jay Freyensee <[email protected]>
Reviewed-by: Matthew Wilcox <[email protected]>
---
include/linux/mm_types.h | 1 +
mm/vmalloc.c | 2 ++
2 files changed, 3 insertions(+)
diff --git a/include/linux/mm_types.h b/include/linux/mm_types.h
index fd1af6b9591d..c3a4825e10c0 100644
--- a/include/linux/mm_types.h
+++ b/include/linux/mm_types.h
@@ -84,6 +84,7 @@ struct page {
void *s_mem; /* slab first object */
atomic_t compound_mapcount; /* first tail page */
/* page_deferred_list().next -- second tail page */
+ struct vm_struct *area;
};
/* Second double word */
diff --git a/mm/vmalloc.c b/mm/vmalloc.c
index ebff729cc956..61a1ca22b0f6 100644
--- a/mm/vmalloc.c
+++ b/mm/vmalloc.c
@@ -1536,6 +1536,7 @@ static void __vunmap(const void *addr, int deallocate_pages)
struct page *page = area->pages[i];
BUG_ON(!page);
+ page->area = NULL;
__free_pages(page, 0);
}
@@ -1705,6 +1706,7 @@ static void *__vmalloc_area_node(struct vm_struct *area, gfp_t gfp_mask,
area->nr_pages = i;
goto fail;
}
+ page->area = area;
area->pages[i] = page;
if (gfpflags_allow_blocking(gfp_mask|highmem_mask))
cond_resched();
--
2.14.1
The MMU available in many systems running Linux can often provide R/O
protection to the memory pages it handles.
However, the MMU-based protection works efficiently only when said pages
contain exclusively data that will not need further modifications.
Statically allocated variables can be segregated into a dedicated
section (that's how __ro_after_init works), but this does not sit very
well with dynamically allocated ones.
Dynamic allocation does not provide, currently, any means for grouping
variables in memory pages that would contain exclusively data suitable
for conversion to read only access mode.
The allocator here provided (pmalloc - protectable memory allocator)
introduces the concept of pools of protectable memory.
A module can instantiate a pool, and then refer any allocation request to
the pool handler it has received.
A pool is organized ias list of areas of virtually contiguous memory.
Whenever the protection functionality is invoked on a pool, all the
areas it contains that are not yet read-only are write-protected.
The process of growing and protecting the pool can be iterated at will.
Each iteration will prevent further allocation from the memory area
currently active, turn it into read-only mode and then proceed to
secure whatever other area might still be unprotected.
Write-protcting some part of a pool before completing all the
allocations can be wasteful, however it will guarrantee the minimum
window of vulnerability, sice the data can be allocated, initialized
and protected in a single sweep.
There are pros and cons, depending on the allocation patterns, the size
of the areas being allocated, the time intervals between initialization
and protection.
Dstroying a pool is the only way to claim back the associated memory.
It is up to its user to avoid any further references to the memory that
was allocated, once the destruction is invoked.
An example where it is desirable to destroy a pool and claim back its
memory is when unloading a kernel module.
A module can have as many pools as needed.
Since pmalloc memory is obtained from vmalloc, an attacker that has
gained access to the physical mapping, still has to identify where the
target of the attack (in virtually contiguous mapping) is located.
Compared to plain vmalloc, pmalloc does not generate as much TLB
trashing, since it can host multiple allocations in the same page,
where present.
Signed-off-by: Igor Stoppa <[email protected]>
---
include/linux/pmalloc.h | 166 ++++++++++++++++++++++++++++++
include/linux/vmalloc.h | 3 +
mm/Kconfig | 6 ++
mm/Makefile | 1 +
mm/pmalloc.c | 264 ++++++++++++++++++++++++++++++++++++++++++++++++
mm/usercopy.c | 33 ++++++
mm/vmalloc.c | 2 +-
7 files changed, 474 insertions(+), 1 deletion(-)
create mode 100644 include/linux/pmalloc.h
create mode 100644 mm/pmalloc.c
diff --git a/include/linux/pmalloc.h b/include/linux/pmalloc.h
new file mode 100644
index 000000000000..07d7838f7877
--- /dev/null
+++ b/include/linux/pmalloc.h
@@ -0,0 +1,166 @@
+/* SPDX-License-Identifier: GPL-2.0 */
+/*
+ * pmalloc.h: Header for Protectable Memory Allocator
+ *
+ * (C) Copyright 2017-18 Huawei Technologies Co. Ltd.
+ * Author: Igor Stoppa <[email protected]>
+ */
+
+#ifndef _LINUX_PMALLOC_H
+#define _LINUX_PMALLOC_H
+
+
+#include <linux/string.h>
+#include <linux/slab.h>
+
+/*
+ * Library for dynamic allocation of pools of protectable memory.
+ * A pool is a single linked list of vmap_area structures.
+ * Whenever a pool is protected, all the areas it contain at that point
+ * are write protected.
+ * More areas can be added and protected, in the same way.
+ * Memory in a pool cannot be individually unprotected, but the pool can
+ * be destroyed.
+ * Upon destruction of a certain pool, all the related memory is released,
+ * including its metadata.
+ *
+ * Pmalloc memory is intended to complement __read_only_after_init.
+ * It can be used, for example, where there is a write-once variable, for
+ * which it is not possible to know the initialization value before init
+ * is completed (which is what __read_only_after_init requires).
+ *
+ * It can be useful also where the amount of data to protect is not known
+ * at compile time and the memory can only be allocated dynamically.
+ *
+ * Finally, it can be useful also when it is desirable to control
+ * dynamically (for example throguh the command line) if something ought
+ * to be protected or not, without having to rebuild the kernel (like in
+ * the build used for a linux distro).
+ */
+
+
+#define PMALLOC_REFILL_DEFAULT (0)
+#define PMALLOC_ALIGN_DEFAULT ARCH_KMALLOC_MINALIGN
+
+struct pmalloc_pool *pmalloc_create_custom_pool(unsigned long int refill,
+ unsigned short align_order);
+
+/**
+ * pmalloc_create_pool() - create a protectable memory pool
+ *
+ * Shorthand for pmalloc_create_custom_pool() with default argument:
+ * * refill is set to PMALLOC_REFILL_DEFAULT
+ * * align_order is set to PMALLOC_ALIGN_DEFAULT
+ *
+ * Return:
+ * * pointer to the new pool - success
+ * * NULL - error
+ */
+static inline struct pmalloc_pool *pmalloc_create_pool(void)
+{
+ return pmalloc_create_custom_pool(PMALLOC_REFILL_DEFAULT,
+ PMALLOC_ALIGN_DEFAULT);
+}
+
+
+void *pmalloc(struct pmalloc_pool *pool, size_t size);
+
+
+/**
+ * pzalloc() - zero-initialized version of pmalloc()
+ * @pool: handle to the pool to be used for memory allocation
+ * @size: amount of memory (in bytes) requested
+ *
+ * Executes pmalloc(), initializing the memory requested to 0, before
+ * returning its address.
+ *
+ * Return:
+ * * pointer to the memory requested - success
+ * * NULL - error
+ */
+static inline void *pzalloc(struct pmalloc_pool *pool, size_t size)
+{
+ void *ptr = pmalloc(pool, size);
+
+ if (likely(ptr))
+ memset(ptr, 0, size);
+ return ptr;
+}
+
+
+/**
+ * pmalloc_array() - array version of pmalloc()
+ * @pool: handle to the pool to be used for memory allocation
+ * @n: number of elements in the array
+ * @size: amount of memory (in bytes) requested for each element
+ *
+ * Executes pmalloc(), on an array.
+ *
+ * Return:
+ * * the pmalloc result - success
+ * * NULL - error
+ */
+
+static inline void *pmalloc_array(struct pmalloc_pool *pool, size_t n,
+ size_t size)
+{
+ if (unlikely(size != 0) && unlikely(n > SIZE_MAX / size))
+ return NULL;
+ return pmalloc(pool, n * size);
+}
+
+
+/**
+ * pcalloc() - array version of pzalloc()
+ * @pool: handle to the pool to be used for memory allocation
+ * @n: number of elements in the array
+ * @size: amount of memory (in bytes) requested for each element
+ *
+ * Executes pzalloc(), on an array.
+ *
+ * Return:
+ * * the pmalloc result - success
+ * * NULL - error
+ */
+static inline void *pcalloc(struct pmalloc_pool *pool, size_t n,
+ size_t size)
+{
+ if (unlikely(size != 0) && unlikely(n > SIZE_MAX / size))
+ return NULL;
+ return pzalloc(pool, n * size);
+}
+
+
+/**
+ * pstrdup() - duplicate a string, using pmalloc()
+ * @pool: handle to the pool to be used for memory allocation
+ * @s: string to duplicate
+ *
+ * Generates a copy of the given string, allocating sufficient memory
+ * from the given pmalloc pool.
+ *
+ * Return:
+ * * pointer to the replica - success
+ * * NULL - error
+ */
+static inline char *pstrdup(struct pmalloc_pool *pool, const char *s)
+{
+ size_t len;
+ char *buf;
+
+ len = strlen(s) + 1;
+ buf = pmalloc(pool, len);
+ if (likely(buf))
+ strncpy(buf, s, len);
+ return buf;
+}
+
+
+void pmalloc_protect_pool(struct pmalloc_pool *pool);
+
+
+void pmalloc_destroy_pool(struct pmalloc_pool *pool);
+
+
+int is_pmalloc_object(const void *ptr, const unsigned long n);
+#endif
diff --git a/include/linux/vmalloc.h b/include/linux/vmalloc.h
index 2d07dfef3cfd..69c12f21200f 100644
--- a/include/linux/vmalloc.h
+++ b/include/linux/vmalloc.h
@@ -20,6 +20,8 @@ struct notifier_block; /* in notifier.h */
#define VM_UNINITIALIZED 0x00000020 /* vm_struct is not fully initialized */
#define VM_NO_GUARD 0x00000040 /* don't add guard page */
#define VM_KASAN 0x00000080 /* has allocated kasan shadow memory */
+#define VM_PMALLOC 0x00000100 /* pmalloc area - see docs */
+#define VM_PMALLOC_PROTECTED 0x00000200 /* protected area - see docs */
/* bits [20..32] reserved for arch specific ioremap internals */
/*
@@ -133,6 +135,7 @@ extern struct vm_struct *__get_vm_area_caller(unsigned long size,
const void *caller);
extern struct vm_struct *remove_vm_area(const void *addr);
extern struct vm_struct *find_vm_area(const void *addr);
+extern struct vmap_area *find_vmap_area(unsigned long addr);
extern int map_vm_area(struct vm_struct *area, pgprot_t prot,
struct page **pages);
diff --git a/mm/Kconfig b/mm/Kconfig
index c782e8fb7235..1ac1dfc60c22 100644
--- a/mm/Kconfig
+++ b/mm/Kconfig
@@ -760,3 +760,9 @@ config GUP_BENCHMARK
performance of get_user_pages_fast().
See tools/testing/selftests/vm/gup_benchmark.c
+
+config PROTECTABLE_MEMORY
+ bool
+ depends on MMU
+ depends on ARCH_HAS_SET_MEMORY
+ default y
diff --git a/mm/Makefile b/mm/Makefile
index e669f02c5a54..959fdbdac118 100644
--- a/mm/Makefile
+++ b/mm/Makefile
@@ -65,6 +65,7 @@ obj-$(CONFIG_SPARSEMEM) += sparse.o
obj-$(CONFIG_SPARSEMEM_VMEMMAP) += sparse-vmemmap.o
obj-$(CONFIG_SLOB) += slob.o
obj-$(CONFIG_MMU_NOTIFIER) += mmu_notifier.o
+obj-$(CONFIG_PROTECTABLE_MEMORY) += pmalloc.o
obj-$(CONFIG_KSM) += ksm.o
obj-$(CONFIG_PAGE_POISONING) += page_poison.o
obj-$(CONFIG_SLAB) += slab.o
diff --git a/mm/pmalloc.c b/mm/pmalloc.c
new file mode 100644
index 000000000000..f659e9006df1
--- /dev/null
+++ b/mm/pmalloc.c
@@ -0,0 +1,264 @@
+// SPDX-License-Identifier: GPL-2.0
+/*
+ * pmalloc.c: Protectable Memory Allocator
+ *
+ * (C) Copyright 2017-2018 Huawei Technologies Co. Ltd.
+ * Author: Igor Stoppa <[email protected]>
+ */
+
+#include <linux/printk.h>
+#include <linux/init.h>
+#include <linux/mm.h>
+#include <linux/vmalloc.h>
+#include <linux/kernel.h>
+#include <linux/log2.h>
+#include <linux/slab.h>
+#include <linux/set_memory.h>
+#include <linux/bug.h>
+#include <linux/mutex.h>
+#include <linux/llist.h>
+#include <asm/cacheflush.h>
+#include <asm/page.h>
+
+#include <linux/pmalloc.h>
+
+#define MAX_ALIGN_ORDER (ilog2(sizeof(void *)))
+struct pmalloc_pool {
+ struct mutex mutex;
+ struct list_head pool_node;
+ struct llist_head vm_areas;
+ unsigned long refill;
+ unsigned long offset;
+ unsigned long align;
+};
+
+static LIST_HEAD(pools_list);
+static DEFINE_MUTEX(pools_mutex);
+
+static inline void tag_area(struct vmap_area *area)
+{
+ area->vm->flags |= VM_PMALLOC;
+}
+
+static inline void untag_area(struct vmap_area *area)
+{
+ area->vm->flags &= ~VM_PMALLOC;
+}
+
+static inline struct vmap_area *current_area(struct pmalloc_pool *pool)
+{
+ return llist_entry(pool->vm_areas.first, struct vmap_area,
+ area_list);
+}
+
+static inline bool is_area_protected(struct vmap_area *area)
+{
+ return area->vm->flags & VM_PMALLOC_PROTECTED;
+}
+
+static inline bool protect_area(struct vmap_area *area)
+{
+ if (unlikely(is_area_protected(area)))
+ return false;
+ set_memory_ro(area->va_start, area->vm->nr_pages);
+ area->vm->flags |= VM_PMALLOC_PROTECTED;
+ return true;
+}
+
+static inline void destroy_area(struct vmap_area *area)
+{
+ WARN(!is_area_protected(area), "Destroying unprotected area.");
+// set_memory_rw(area->va_start, area->vm->nr_pages); //XXX Skip it?
+ vfree((void *)area->va_start);
+}
+
+static inline bool empty(struct pmalloc_pool *pool)
+{
+ return unlikely(llist_empty(&pool->vm_areas));
+}
+
+static inline bool protected(struct pmalloc_pool *pool)
+{
+ return is_area_protected(current_area(pool));
+}
+
+static inline bool exhausted(struct pmalloc_pool *pool, size_t size)
+{
+ unsigned long space_before;
+ unsigned long space_after;
+
+ space_before = round_down(pool->offset, pool->align);
+ space_after = pool->offset - space_before;
+ return unlikely(space_after < size && space_before < size);
+}
+
+static inline bool space_needed(struct pmalloc_pool *pool, size_t size)
+{
+ return empty(pool) || protected(pool) || exhausted(pool, size);
+}
+
+#define DEFAULT_REFILL_SIZE PAGE_SIZE
+/**
+ * pmalloc_create_custom_pool() - create a new protectable memory pool
+ * @refill: the minimum size to allocate when in need of more memory.
+ * It will be rounded up to a multiple of PAGE_SIZE
+ * The value of 0 gives the default amount of PAGE_SIZE.
+ * @align_order: log2 of the alignment to use when allocating memory
+ * Negative values give ARCH_KMALLOC_MINALIGN
+ *
+ * Creates a new (empty) memory pool for allocation of protectable
+ * memory. Memory will be allocated upon request (through pmalloc).
+ *
+ * Return:
+ * * pointer to the new pool - success
+ * * NULL - error
+ */
+struct pmalloc_pool *pmalloc_create_custom_pool(unsigned long refill,
+ unsigned short align_order)
+{
+ struct pmalloc_pool *pool;
+
+ pool = kzalloc(sizeof(struct pmalloc_pool), GFP_KERNEL);
+ if (WARN(!pool, "Could not allocate pool meta data."))
+ return NULL;
+
+ pool->refill = refill ? PAGE_ALIGN(refill) : DEFAULT_REFILL_SIZE;
+ pool->align = 1UL << align_order;
+ mutex_init(&pool->mutex);
+
+ mutex_lock(&pools_mutex);
+ list_add(&pool->pool_node, &pools_list);
+ mutex_unlock(&pools_mutex);
+ return pool;
+}
+
+
+static int grow(struct pmalloc_pool *pool, size_t size)
+{
+ void *addr;
+ struct vmap_area *area;
+
+ addr = vmalloc(max(size, pool->refill));
+ if (WARN(!addr, "Failed to allocate %zd bytes", PAGE_ALIGN(size)))
+ return -ENOMEM;
+
+ area = find_vmap_area((unsigned long)addr);
+ tag_area(area);
+ pool->offset = area->vm->nr_pages * PAGE_SIZE;
+ llist_add(&area->area_list, &pool->vm_areas);
+ return 0;
+}
+
+static unsigned long reserve_mem(struct pmalloc_pool *pool, size_t size)
+{
+ pool->offset = round_down(pool->offset - size, pool->align);
+ return current_area(pool)->va_start + pool->offset;
+
+}
+
+/**
+ * pmalloc() - allocate protectable memory from a pool
+ * @pool: handle to the pool to be used for memory allocation
+ * @size: amount of memory (in bytes) requested
+ *
+ * Allocates memory from a pool.
+ * If needed, the pool will automatically allocate enough memory to
+ * either satisfy the request or meet the "refill" parameter received
+ * upon creation.
+ * New allocation can happen also if the current memory in the pool is
+ * already write protected.
+ *
+ * Return:
+ * * pointer to the memory requested - success
+ * * NULL - error
+ */
+void *pmalloc(struct pmalloc_pool *pool, size_t size)
+{
+ unsigned long retval = 0;
+
+ mutex_lock(&pool->mutex);
+ if (unlikely(space_needed(pool, size)) &&
+ unlikely(grow(pool, size)))
+ goto out;
+ retval = reserve_mem(pool, size);
+out:
+ mutex_unlock(&pool->mutex);
+ return (void *)retval;
+}
+
+/**
+ * pmalloc_protect_pool() - write-protects the memory in the pool
+ * @pool: the pool associated tothe memory to write-protect
+ *
+ * Write-protects all the memory areas currently assigned to the pool
+ * that are still unprotected.
+ * This does not prevent further allocation of additional memory, that
+ * can be initialized and protected.
+ * The catch is that protecting a pool will make unavailable whatever
+ * free memory it might still contain.
+ * Successive allocations will grab more free pages.
+ */
+void pmalloc_protect_pool(struct pmalloc_pool *pool)
+{
+ struct vmap_area *area;
+
+ mutex_lock(&pool->mutex);
+ llist_for_each_entry(area, pool->vm_areas.first, area_list)
+ if (unlikely(!protect_area(area)))
+ break;
+ mutex_unlock(&pool->mutex);
+}
+
+
+/**
+ * is_pmalloc_object() - test if the given range is within a pmalloc pool
+ * @ptr: the base address of the range
+ * @n: the size of the range
+ *
+ * Return:
+ * * true - the range given is fully within a pmalloc pool
+ * * false - the range given is not fully within a pmalloc pool
+ */
+int is_pmalloc_object(const void *ptr, const unsigned long n)
+{
+ struct vm_struct *area;
+
+ if (likely(!is_vmalloc_addr(ptr)))
+ return false;
+
+ area = vmalloc_to_page(ptr)->area;
+ if (unlikely(!(area->flags & VM_PMALLOC)))
+ return false;
+
+ return ((n + (unsigned long)ptr) <=
+ (area->nr_pages * PAGE_SIZE + (unsigned long)area->addr));
+
+}
+
+
+/**
+ * pmalloc_destroy_pool() - destroys a pool and all the associated memory
+ * @pool: the pool to destroy
+ *
+ * All the memory associated to the pool will be freed, including the
+ * metadata used for the pool.
+ */
+void pmalloc_destroy_pool(struct pmalloc_pool *pool)
+{
+ struct vmap_area *area;
+ struct llist_node *cursor;
+ struct llist_node *tmp;
+
+ mutex_lock(&pools_mutex);
+ list_del(&pool->pool_node);
+ mutex_unlock(&pools_mutex);
+
+ cursor = pool->vm_areas.first;
+ kfree(pool);
+ while (cursor) { /* iteration over llist */
+ tmp = cursor;
+ cursor = cursor->next;
+ area = llist_entry(tmp, struct vmap_area, area_list);
+ destroy_area(area);
+ }
+}
diff --git a/mm/usercopy.c b/mm/usercopy.c
index e9e9325f7638..946ce051e296 100644
--- a/mm/usercopy.c
+++ b/mm/usercopy.c
@@ -240,6 +240,36 @@ static inline void check_heap_object(const void *ptr, unsigned long n,
}
}
+#ifdef CONFIG_PROTECTABLE_MEMORY
+
+int is_pmalloc_object(const void *ptr, const unsigned long n);
+
+static void check_pmalloc_object(const void *ptr, unsigned long n,
+ bool to_user)
+{
+ int retv;
+
+ retv = is_pmalloc_object(ptr, n);
+ if (unlikely(retv)) {
+ if (unlikely(!to_user))
+ usercopy_abort("pmalloc",
+ "trying to write to pmalloc object",
+ to_user, (const unsigned long)ptr, n);
+ if (retv < 0)
+ usercopy_abort("pmalloc",
+ "invalid pmalloc object",
+ to_user, (const unsigned long)ptr, n);
+ }
+}
+
+#else
+
+static void check_pmalloc_object(const void *ptr, unsigned long n,
+ bool to_user)
+{
+}
+#endif
+
/*
* Validates that the given object is:
* - not bogus address
@@ -277,5 +307,8 @@ void __check_object_size(const void *ptr, unsigned long n, bool to_user)
/* Check for object in kernel to avoid text exposure. */
check_kernel_text_object((const unsigned long)ptr, n, to_user);
+
+ /* Check if object is from a pmalloc chunk. */
+ check_pmalloc_object(ptr, n, to_user);
}
EXPORT_SYMBOL(__check_object_size);
diff --git a/mm/vmalloc.c b/mm/vmalloc.c
index 1bb2233bb262..da9cc9cd8b52 100644
--- a/mm/vmalloc.c
+++ b/mm/vmalloc.c
@@ -759,7 +759,7 @@ static void free_unmap_vmap_area(struct vmap_area *va)
free_vmap_area_noflush(va);
}
-static struct vmap_area *find_vmap_area(unsigned long addr)
+struct vmap_area *find_vmap_area(unsigned long addr)
{
struct vmap_area *va;
--
2.14.1
The vmap_area structure has a field of type struct llist_node, named
purge_list and is used when performing lazy purge of the area.
Such field is left unused during the actual utilization of the
structure.
This patch renames the field to a more generic "area_list", to allow for
utilization outside of the purging phase.
Since the purging happens after the vmap_area is dismissed, its use is
mutually exclusive with any use performed while the area is allocated.
Signed-off-by: Igor Stoppa <[email protected]>
---
include/linux/vmalloc.h | 2 +-
mm/vmalloc.c | 6 +++---
2 files changed, 4 insertions(+), 4 deletions(-)
diff --git a/include/linux/vmalloc.h b/include/linux/vmalloc.h
index 1e5d8c392f15..2d07dfef3cfd 100644
--- a/include/linux/vmalloc.h
+++ b/include/linux/vmalloc.h
@@ -47,7 +47,7 @@ struct vmap_area {
unsigned long flags;
struct rb_node rb_node; /* address sorted rbtree */
struct list_head list; /* address sorted list */
- struct llist_node purge_list; /* "lazy purge" list */
+ struct llist_node area_list; /* generic list of areas */
struct vm_struct *vm;
struct rcu_head rcu_head;
};
diff --git a/mm/vmalloc.c b/mm/vmalloc.c
index 61a1ca22b0f6..1bb2233bb262 100644
--- a/mm/vmalloc.c
+++ b/mm/vmalloc.c
@@ -682,7 +682,7 @@ static bool __purge_vmap_area_lazy(unsigned long start, unsigned long end)
lockdep_assert_held(&vmap_purge_lock);
valist = llist_del_all(&vmap_purge_list);
- llist_for_each_entry(va, valist, purge_list) {
+ llist_for_each_entry(va, valist, area_list) {
if (va->va_start < start)
start = va->va_start;
if (va->va_end > end)
@@ -696,7 +696,7 @@ static bool __purge_vmap_area_lazy(unsigned long start, unsigned long end)
flush_tlb_kernel_range(start, end);
spin_lock(&vmap_area_lock);
- llist_for_each_entry_safe(va, n_va, valist, purge_list) {
+ llist_for_each_entry_safe(va, n_va, valist, area_list) {
int nr = (va->va_end - va->va_start) >> PAGE_SHIFT;
__free_vmap_area(va);
@@ -743,7 +743,7 @@ static void free_vmap_area_noflush(struct vmap_area *va)
&vmap_lazy_nr);
/* After this point, we may free va at any time */
- llist_add(&va->purge_list, &vmap_purge_list);
+ llist_add(&va->area_list, &vmap_purge_list);
if (unlikely(nr_lazy > lazy_max_pages()))
try_purge_vmap_area_lazy();
--
2.14.1
Add basic self-test functionality for pmalloc.
The testing is introduced as early as possible, right after the main
dependency, genalloc, has passed successfully, so that it can help
diagnosing failures in pmalloc users.
Signed-off-by: Igor Stoppa <[email protected]>
---
include/linux/test_pmalloc.h | 24 ++++++++
init/main.c | 2 +
mm/Kconfig | 10 ++++
mm/Makefile | 1 +
mm/test_pmalloc.c | 136 +++++++++++++++++++++++++++++++++++++++++++
5 files changed, 173 insertions(+)
create mode 100644 include/linux/test_pmalloc.h
create mode 100644 mm/test_pmalloc.c
diff --git a/include/linux/test_pmalloc.h b/include/linux/test_pmalloc.h
new file mode 100644
index 000000000000..c7e2e451c17c
--- /dev/null
+++ b/include/linux/test_pmalloc.h
@@ -0,0 +1,24 @@
+/* SPDX-License-Identifier: GPL-2.0 */
+/*
+ * test_pmalloc.h
+ *
+ * (C) Copyright 2018 Huawei Technologies Co. Ltd.
+ * Author: Igor Stoppa <[email protected]>
+ */
+
+
+#ifndef __LINUX_TEST_PMALLOC_H
+#define __LINUX_TEST_PMALLOC_H
+
+
+#ifdef CONFIG_TEST_PROTECTABLE_MEMORY
+
+void test_pmalloc(void);
+
+#else
+
+static inline void test_pmalloc(void){};
+
+#endif
+
+#endif
diff --git a/init/main.c b/init/main.c
index 21efbf6ace93..c63c41a33c9b 100644
--- a/init/main.c
+++ b/init/main.c
@@ -90,6 +90,7 @@
#include <linux/cache.h>
#include <linux/rodata_test.h>
#include <linux/jump_label.h>
+#include <linux/test_pmalloc.h>
#include <asm/io.h>
#include <asm/bugs.h>
@@ -661,6 +662,7 @@ asmlinkage __visible void __init start_kernel(void)
*/
mem_encrypt_init();
+ test_pmalloc();
#ifdef CONFIG_BLK_DEV_INITRD
if (initrd_start && !initrd_below_start_ok &&
page_to_pfn(virt_to_page((void *)initrd_start)) < min_low_pfn) {
diff --git a/mm/Kconfig b/mm/Kconfig
index 1ac1dfc60c22..246f66c7e694 100644
--- a/mm/Kconfig
+++ b/mm/Kconfig
@@ -766,3 +766,13 @@ config PROTECTABLE_MEMORY
depends on MMU
depends on ARCH_HAS_SET_MEMORY
default y
+
+config TEST_PROTECTABLE_MEMORY
+ bool "Run self test for pmalloc memory allocator"
+ depends on MMU
+ depends on ARCH_HAS_SET_MEMORY
+ select PROTECTABLE_MEMORY
+ default n
+ help
+ Tries to verify that pmalloc works correctly and that the memory
+ is effectively protected.
diff --git a/mm/Makefile b/mm/Makefile
index 959fdbdac118..1de4be5fd0bc 100644
--- a/mm/Makefile
+++ b/mm/Makefile
@@ -66,6 +66,7 @@ obj-$(CONFIG_SPARSEMEM_VMEMMAP) += sparse-vmemmap.o
obj-$(CONFIG_SLOB) += slob.o
obj-$(CONFIG_MMU_NOTIFIER) += mmu_notifier.o
obj-$(CONFIG_PROTECTABLE_MEMORY) += pmalloc.o
+obj-$(CONFIG_TEST_PROTECTABLE_MEMORY) += test_pmalloc.o
obj-$(CONFIG_KSM) += ksm.o
obj-$(CONFIG_PAGE_POISONING) += page_poison.o
obj-$(CONFIG_SLAB) += slab.o
diff --git a/mm/test_pmalloc.c b/mm/test_pmalloc.c
new file mode 100644
index 000000000000..08274b0324f9
--- /dev/null
+++ b/mm/test_pmalloc.c
@@ -0,0 +1,136 @@
+// SPDX-License-Identifier: GPL-2.0
+/*
+ * test_pmalloc.c
+ *
+ * (C) Copyright 2018 Huawei Technologies Co. Ltd.
+ * Author: Igor Stoppa <[email protected]>
+ */
+
+#include <linux/pmalloc.h>
+#include <linux/mm.h>
+#include <linux/test_pmalloc.h>
+#include <linux/bug.h>
+
+#define SIZE_1 (PAGE_SIZE * 3)
+#define SIZE_2 1000
+
+
+/* wrapper for is_pmalloc_object() with messages */
+static inline bool validate_alloc(bool expected, void *addr,
+ unsigned long size)
+{
+ bool test;
+
+ test = is_pmalloc_object(addr, size) > 0;
+ pr_notice("must be %s: %s",
+ expected ? "ok" : "no", test ? "ok" : "no");
+ return test == expected;
+}
+
+
+#define is_alloc_ok(variable, size) \
+ validate_alloc(true, variable, size)
+
+
+#define is_alloc_no(variable, size) \
+ validate_alloc(false, variable, size)
+
+/* tests the basic life-cycle of a pool */
+static bool create_and_destroy_pool(void)
+{
+ static struct pmalloc_pool *pool;
+
+ pr_notice("Testing pool creation and destruction capability");
+
+ pool = pmalloc_create_pool();
+ if (WARN(!pool, "Cannot allocate memory for pmalloc selftest."))
+ return false;
+ pmalloc_destroy_pool(pool);
+ return true;
+}
+
+
+/* verifies that it's possible to allocate from the pool */
+static bool test_alloc(void)
+{
+ static struct pmalloc_pool *pool;
+ static void *p;
+
+ pr_notice("Testing allocation capability");
+ pool = pmalloc_create_pool();
+ if (WARN(!pool, "Unable to allocate memory for pmalloc selftest."))
+ return false;
+ p = pmalloc(pool, SIZE_1 - 1);
+ pmalloc_protect_pool(pool);
+ pmalloc_destroy_pool(pool);
+ if (WARN(!p, "Failed to allocate memory from the pool"))
+ return false;
+ return true;
+}
+
+
+/* tests the identification of pmalloc ranges */
+static bool test_is_pmalloc_object(void)
+{
+ struct pmalloc_pool *pool;
+ void *pmalloc_p;
+ void *vmalloc_p;
+ bool retval = false;
+
+ pr_notice("Test correctness of is_pmalloc_object()");
+
+ vmalloc_p = vmalloc(SIZE_1);
+ if (WARN(!vmalloc_p,
+ "Unable to allocate memory for pmalloc selftest."))
+ return false;
+ pool = pmalloc_create_pool();
+ if (WARN(!pool, "Unable to allocate memory for pmalloc selftest."))
+ return false;
+ pmalloc_p = pmalloc(pool, SIZE_1 - 1);
+ if (WARN(!pmalloc_p, "Failed to allocate memory from the pool"))
+ goto error;
+ if (WARN_ON(unlikely(!is_alloc_ok(pmalloc_p, 10))) ||
+ WARN_ON(unlikely(!is_alloc_ok(pmalloc_p, SIZE_1))) ||
+ WARN_ON(unlikely(!is_alloc_ok(pmalloc_p, PAGE_SIZE))) ||
+ WARN_ON(unlikely(!is_alloc_no(pmalloc_p, SIZE_1 + 1))) ||
+ WARN_ON(unlikely(!is_alloc_no(vmalloc_p, 10))))
+ goto error;
+ retval = true;
+error:
+ pmalloc_protect_pool(pool);
+ pmalloc_destroy_pool(pool);
+ return retval;
+}
+
+/* Test out of virtually contiguous memory */
+static void test_oovm(void)
+{
+ struct pmalloc_pool *pool;
+ int i;
+
+ pr_notice("Exhaust vmalloc memory with doubling allocations.");
+ pool = pmalloc_create_pool();
+ if (WARN(!pool, "Failed to create pool"))
+ return;
+ for (i = 1; i; i *= 2)
+ if (unlikely(!pzalloc(pool, i - 1)))
+ break;
+ pr_notice("vmalloc oom at %d allocation", i - 1);
+ pmalloc_protect_pool(pool);
+ pmalloc_destroy_pool(pool);
+}
+
+/**
+ * test_pmalloc() -main entry point for running the test cases
+ */
+void test_pmalloc(void)
+{
+
+ pr_notice("pmalloc-selftest");
+
+ if (unlikely(!(create_and_destroy_pool() &&
+ test_alloc() &&
+ test_is_pmalloc_object())))
+ return;
+ test_oovm();
+}
--
2.14.1
Verify that pmalloc read-only protection is in place: trying to
overwrite a protected variable will crash the kernel.
Signed-off-by: Igor Stoppa <[email protected]>
---
drivers/misc/lkdtm.h | 1 +
drivers/misc/lkdtm_core.c | 3 +++
drivers/misc/lkdtm_perms.c | 25 +++++++++++++++++++++++++
3 files changed, 29 insertions(+)
diff --git a/drivers/misc/lkdtm.h b/drivers/misc/lkdtm.h
index 9e513dcfd809..dcda3ae76ceb 100644
--- a/drivers/misc/lkdtm.h
+++ b/drivers/misc/lkdtm.h
@@ -38,6 +38,7 @@ void lkdtm_READ_BUDDY_AFTER_FREE(void);
void __init lkdtm_perms_init(void);
void lkdtm_WRITE_RO(void);
void lkdtm_WRITE_RO_AFTER_INIT(void);
+void lkdtm_WRITE_RO_PMALLOC(void);
void lkdtm_WRITE_KERN(void);
void lkdtm_EXEC_DATA(void);
void lkdtm_EXEC_STACK(void);
diff --git a/drivers/misc/lkdtm_core.c b/drivers/misc/lkdtm_core.c
index 2154d1bfd18b..c9fd42bda6ee 100644
--- a/drivers/misc/lkdtm_core.c
+++ b/drivers/misc/lkdtm_core.c
@@ -155,6 +155,9 @@ static const struct crashtype crashtypes[] = {
CRASHTYPE(ACCESS_USERSPACE),
CRASHTYPE(WRITE_RO),
CRASHTYPE(WRITE_RO_AFTER_INIT),
+#ifdef CONFIG_PROTECTABLE_MEMORY
+ CRASHTYPE(WRITE_RO_PMALLOC),
+#endif
CRASHTYPE(WRITE_KERN),
CRASHTYPE(REFCOUNT_INC_OVERFLOW),
CRASHTYPE(REFCOUNT_ADD_OVERFLOW),
diff --git a/drivers/misc/lkdtm_perms.c b/drivers/misc/lkdtm_perms.c
index 53b85c9d16b8..4660ff0bfa44 100644
--- a/drivers/misc/lkdtm_perms.c
+++ b/drivers/misc/lkdtm_perms.c
@@ -9,6 +9,7 @@
#include <linux/vmalloc.h>
#include <linux/mman.h>
#include <linux/uaccess.h>
+#include <linux/pmalloc.h>
#include <asm/cacheflush.h>
/* Whether or not to fill the target memory area with do_nothing(). */
@@ -104,6 +105,30 @@ void lkdtm_WRITE_RO_AFTER_INIT(void)
*ptr ^= 0xabcd1234;
}
+#ifdef CONFIG_PROTECTABLE_MEMORY
+void lkdtm_WRITE_RO_PMALLOC(void)
+{
+ struct pmalloc_pool *pool;
+ int *i;
+
+ pool = pmalloc_create_pool();
+ if (WARN(!pool, "Failed preparing pool for pmalloc test."))
+ return;
+
+ i = (int *)pmalloc(pool, sizeof(int));
+ if (WARN(!i, "Failed allocating memory for pmalloc test.")) {
+ pmalloc_destroy_pool(pool);
+ return;
+ }
+
+ *i = INT_MAX;
+ pmalloc_protect_pool(pool);
+
+ pr_info("attempting bad pmalloc write at %p\n", i);
+ *i = 0;
+}
+#endif
+
void lkdtm_WRITE_KERN(void)
{
size_t size;
--
2.14.1
Detailed documentation about the protectable memory allocator.
Signed-off-by: Igor Stoppa <[email protected]>
---
Documentation/core-api/index.rst | 1 +
Documentation/core-api/pmalloc.rst | 107 +++++++++++++++++++++++++++++++++++++
2 files changed, 108 insertions(+)
create mode 100644 Documentation/core-api/pmalloc.rst
diff --git a/Documentation/core-api/index.rst b/Documentation/core-api/index.rst
index c670a8031786..8f5de42d6571 100644
--- a/Documentation/core-api/index.rst
+++ b/Documentation/core-api/index.rst
@@ -25,6 +25,7 @@ Core utilities
genalloc
errseq
printk-formats
+ pmalloc
Interfaces for kernel debugging
===============================
diff --git a/Documentation/core-api/pmalloc.rst b/Documentation/core-api/pmalloc.rst
new file mode 100644
index 000000000000..c14907485137
--- /dev/null
+++ b/Documentation/core-api/pmalloc.rst
@@ -0,0 +1,107 @@
+.. SPDX-License-Identifier: GPL-2.0
+
+.. _pmalloc:
+
+Protectable memory allocator
+============================
+
+Purpose
+-------
+
+The pmalloc library is meant to provide read-only status to data that,
+for some reason, could neither be declared as constant, nor could it take
+advantage of the qualifier __ro_after_init, but is write-once and
+read-only in spirit. At least as long as it doesn't get teared down.
+It protects data from both accidental and malicious overwrites.
+
+Example: A policy that is loaded from userspace.
+
+
+Concept
+-------
+
+The MMU available in the system can be used to write protect memory pages.
+Unfortunately this feature cannot be used as-it-is, to protect sensitive
+data, because this potentially read-only data is typically interleaved
+with other data, which must stay writeable.
+
+pmalloc introduces the concept of protectable memory pools.
+A pool contains a list of areas of virtually contiguous pages of
+memory. An area is the minimum amount of memory that pmalloc allows to
+protect, because the user might have allocated a memory range that
+crosses the boundary between pages.
+
+When an allocation is performed, if there is not enough memory already
+available in the pool, a new area of suitable size is grabbed.
+The size chosen is the largest between the roundup (to PAGE_SIZE) of
+the request from pmalloc and friends and the refill parameter specified
+when creating the pool.
+
+When a pool is created, it is possible to specify two parameters:
+- refill size: the minimum size of the memory area to allocate when needed
+- align_order: the default alignment to use when reserving memory
+
+To facilitate the conversion of existing code to pmalloc pools, several
+helper functions are provided, mirroring their k/vmalloc counterparts.
+However one is missing. There is no pfree() because the memory protected
+by a pool will be released exclusively when the pool is destroyed.
+
+
+
+Caveats
+-------
+
+- When a pool is protected, whatever memory would be still available in
+ the current vmap_area (from which allocations are performed) is
+ relinquished.
+
+- As already explained, freeing of memory is not supported. Pages will be
+ returned to the system upon destruction of the memory pool that they
+ belong to.
+
+- The address range available for vmalloc (and thus for pmalloc too) is
+ limited, on 32-bit systems. However it shouldn't be an issue, since not
+ much data is expected tobe dynamically allocated and turned into
+ read-only.
+
+- Regarding SMP systems, the allocations are expected to happen mostly
+ during an initial transient, after which there should be no more need
+ to perform cross-processor synchronizations of page tables.
+ Loading of kernel modules is an exception to this, but it's not expected
+ to happen with such high frequency to become a problem.
+
+
+Use
+---
+
+The typical sequence, when using pmalloc, is:
+
+#. create a pool
+
+ :c:func:`pmalloc_create_pool`
+
+#. issue one or more allocation requests to the pool
+
+ :c:func:`pmalloc`
+
+ or
+
+ :c:func:`pzalloc`
+
+#. initialize the memory obtained, with the desired values
+
+#. write-protect the memory so far allocated
+
+ :c::func:`pmalloc_protect_pool`
+
+#. iterate over the last 3 points as needed
+
+#. [optional] destroy the pool
+
+ :c:func:`pmalloc_destroy_pool`
+
+API
+---
+
+.. kernel-doc:: include/linux/pmalloc.h
+.. kernel-doc:: mm/pmalloc.c
--
2.14.1
On Tue, 27 Mar 2018 18:37:36 +0300
Igor Stoppa <[email protected]> wrote:
> This patch-set introduces the possibility of protecting memory that has
> been allocated dynamically.
One thing that jumps out at me as I look at the patch set is: you do not
include any users of this functionality. Where do you expect this
allocator to be used? Actually seeing the API in action would be a useful
addition, I think.
Thanks,
jon
On 27/03/18 20:55, Jonathan Corbet wrote:
> On Tue, 27 Mar 2018 18:37:36 +0300
> Igor Stoppa <[email protected]> wrote:
>
>> This patch-set introduces the possibility of protecting memory that has
>> been allocated dynamically.
>
> One thing that jumps out at me as I look at the patch set is: you do not
> include any users of this functionality. Where do you expect this
> allocator to be used? Actually seeing the API in action would be a useful
> addition, I think.
Yes, this is very true.
Initially I had in mind to use LSM hooks as easy example, but sadly they
seem to be in an almost constant flux.
My real use case is to secure both those and the SELinux policy DB.
I have said this few times, but it didn't seem to be worth mentioning in
the cover letter.
I was hoping to get this merged and then attack both LSM and SELinux,
but it didn't fly, so few months ago i decided to try it all together
and put on hold my efforts to get pmalloc merged.
However, in January, happened this:
http://www.openwall.com/lists/kernel-hardening/2018/01/24/1
which rekindled my hopes to get pmalloc in first, as it would make my
life easier in proposing the changes to SELinux, if they ar ebased on a
nAPI that is already merged.
So I hope that, once both API and implementation for pmalloc are in good
shape, xfs could be the first customer.
If that doesn't happen, I'll go back to the initial plan. Or look for
some other easier target.
Also the IMA policy could benefit from pmalloc protection, I think, I
spent about a week hacking on it and it seems feasible.
But it's not exactly small either.
I do not know if I should have followed some other path, but I'm having
a bit of a hard time, since the API is objectively touching core
functionality, and the change I'd like to use as example affects such a
large component a SELinux.
--
igor
On Fri, 30 Mar 2018 00:25:22 +0400
Igor Stoppa <[email protected]> wrote:
> On 27/03/18 20:55, Jonathan Corbet wrote:
> > On Tue, 27 Mar 2018 18:37:36 +0300
> > Igor Stoppa <[email protected]> wrote:
> >
> >> This patch-set introduces the possibility of protecting memory that has
> >> been allocated dynamically.
> >
> > One thing that jumps out at me as I look at the patch set is: you do not
> > include any users of this functionality. Where do you expect this
> > allocator to be used? Actually seeing the API in action would be a useful
> > addition, I think.
>
> Yes, this is very true.
> Initially I had in mind to use LSM hooks as easy example, but sadly they
> seem to be in an almost constant flux.
>
> My real use case is to secure both those and the SELinux policy DB.
> I have said this few times, but it didn't seem to be worth mentioning in
> the cover letter.
In general, it is quite hard to merge a new API without users to go along
with it. Among other things, that's how reviewers can see how well the
API works in real-world use. I am certainly not the one who will make the
decision on whether this goes in, but I suspect that whoever *does* make
that decision would prefer to see some users.
Thanks,
jon