Re: [PATCH 4/7] Protectable Memory

[J Freyensee]

On 2/23/18 6:48 AM, Igor Stoppa wrote:

> 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, 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 request a pool and then refer any allocation request to the
> pool handler it has received.
>
> Once all the chunks of memory associated to a specific pool are
> initialized, the pool can be protected.
>
> After this point, the pool can only be destroyed (it is up to the module
> to avoid any further references to the memory from the pool, after
> the destruction is invoked).
>
> The latter case is mainly meant for releasing memory, when a module is
> unloaded.
>
> A module can have as many pools as needed, for example to support the
> protection of data that is initialized in sufficiently distinct phases.
>
> 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 is actually located.
>
> At the same time, being also based on genalloc, pmalloc does not
> generate as much trashing of the TLB as it would be caused by using
> directly only vmalloc.
>
> Signed-off-by: Igor Stoppa <igor.stoppa@xxxxxxxxxx>
> ---
>   include/linux/genalloc.h |   3 +
>   include/linux/pmalloc.h  | 242 +++++++++++++++++++++++
>   include/linux/vmalloc.h  |   1 +
>   lib/genalloc.c           |  27 +++
>   mm/Kconfig               |   6 +
>   mm/Makefile              |   1 +
>   mm/pmalloc.c             | 499 +++++++++++++++++++++++++++++++++++++++++++++++
>   mm/usercopy.c            |  33 ++++
>   8 files changed, 812 insertions(+)
>   create mode 100644 include/linux/pmalloc.h
>   create mode 100644 mm/pmalloc.c
>
> diff --git a/include/linux/genalloc.h b/include/linux/genalloc.h
> index dcaa33e74b1c..b6c4cea9fbd8 100644
> --- a/include/linux/genalloc.h
> +++ b/include/linux/genalloc.h
> @@ -121,6 +121,9 @@ extern unsigned long gen_pool_alloc_algo(struct gen_pool *, size_t,
>   extern void *gen_pool_dma_alloc(struct gen_pool *pool, size_t size,
>   		dma_addr_t *dma);
>   extern void gen_pool_free(struct gen_pool *, unsigned long, size_t);
> +
> +extern void gen_pool_flush_chunk(struct gen_pool *pool,
> +				 struct gen_pool_chunk *chunk);
>   extern void gen_pool_for_each_chunk(struct gen_pool *,
>   	void (*)(struct gen_pool *, struct gen_pool_chunk *, void *), void *);
>   extern size_t gen_pool_avail(struct gen_pool *);
> diff --git a/include/linux/pmalloc.h b/include/linux/pmalloc.h
> new file mode 100644
> index 000000000000..afc2068d5545
> --- /dev/null
> +++ b/include/linux/pmalloc.h
> @@ -0,0 +1,242 @@
> +/* SPDX-License-Identifier: GPL-2.0 */
> +/*
> + * pmalloc.h: Header for Protectable Memory Allocator
> + *
> + * (C) Copyright 2017 Huawei Technologies Co. Ltd.
> + * Author: Igor Stoppa <igor.stoppa@xxxxxxxxxx>
> + */
> +
> +#ifndef _LINUX_PMALLOC_H
> +#define _LINUX_PMALLOC_H
> +
> +
> +#include <linux/genalloc.h>
> +#include <linux/string.h>
> +
> +#define PMALLOC_DEFAULT_ALLOC_ORDER (-1)
> +
> +/*
> + * Library for dynamic allocation of pools of memory that can be,
> + * after initialization, marked as read-only.
> + *
> + * This is intended to complement __read_only_after_init, for those cases
> + * where either it is not possible to know the initialization value before
> + * init is completed, or the amount of data is variable and can be
> + * determined only at run-time.
> + *
> + * ***WARNING***
> + * The user of the API is expected to synchronize:
> + * 1) allocation,
> + * 2) writes to the allocated memory,
> + * 3) write protection of the pool,
> + * 4) freeing of the allocated memory, and
> + * 5) destruction of the pool.
> + *
> + * For a non-threaded scenario, this type of locking is not even required.
> + *
> + * Even if the library were to provide support for locking, point 2)
> + * would still depend on the user taking the lock.
> + */
> +
> +
> +/**
> + * pmalloc_create_pool() - create a new protectable memory pool
> + * @name: the name of the pool, enforced to be unique
> + * @min_alloc_order: log2 of the minimum allocation size obtainable
> + *                   from the pool
> + *
> + * 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 gen_pool *pmalloc_create_pool(const char *name,
> +					 int min_alloc_order);

Same comments as earlier. If this is new API with new code being 
introduced into the kernel, can the variables be declared to avoid weird 
problems? Like min_alloc_order being a negative value makes little 
sense (based on the description here), so can it be declared as size_t 
or unsigned int?
> +
> +/**
> + * is_pmalloc_object() - validates the existence of an alleged object
> + * @ptr: address of the object
> + * @n: size of the object, in bytes
> + *
> + * Return:
> + * * 0		- the object does not belong to pmalloc
> + * * 1		- the object belongs to pmalloc
> + * * \-1	- the object overlaps pmalloc memory incorrectly
> + */
> +int is_pmalloc_object(const void *ptr, const unsigned long n);
> +
> +/**
> + * pmalloc_prealloc() - tries to allocate a memory chunk of the requested size
> + * @pool: handle to the pool to be used for memory allocation
> + * @size: amount of memory (in bytes) requested
> + *
> + * Prepares a chunk of the requested size.
> + * This is intended to both minimize latency in later memory requests and
> + * avoid sleeping during allocation.
> + * Memory allocated with prealloc is stored in one single chunk, as
> + * opposed to what is allocated on-demand when pmalloc runs out of free
> + * space already existing in the pool and has to invoke vmalloc.
> + * One additional advantage of pre-allocating larger chunks of memory is
> + * that the total slack tends to be smaller.
> + *
> + * Return:
> + * * true	- the vmalloc call was successful
> + * * false	- error
> + */
> +bool pmalloc_prealloc(struct gen_pool *pool, size_t size);
> +
> +/**
> + * 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
> + * @gfp: flags for page allocation
> + *
> + * Allocates memory from an unprotected pool. If the pool doesn't have
> + * enough memory, and the request did not include GFP_ATOMIC, an attempt
> + * is made to add a new chunk of memory to the pool
> + * (a multiple of PAGE_SIZE), in order to fit the new request.
> + * Otherwise, NULL is returned.
> + *
> + * Return:
> + * * pointer to the memory requested	- success
> + * * NULL				- either no memory available or
> + *					  pool already read-only
> + */

I don't know if an errno value is being set, but setting a variable 
somewhere using EROFS or ENOMEM would more accurate diagnose those two 
NULL conditions.
> +void *pmalloc(struct gen_pool *pool, size_t size, gfp_t gfp);
> +
> +
> +/**
> + * pzalloc() - zero-initialized version of pmalloc
> + * @pool: handle to the pool to be used for memory allocation
> + * @size: amount of memory (in bytes) requested
> + * @gfp: flags for page allocation
> + *
> + * Executes pmalloc, initializing the memory requested to 0,
> + * before returning the pointer to it.
> + *
> + * Return:
> + * * pointer to the memory requested	- success
> + * * NULL				- either no memory available or
> + *					  pool already read-only
> + */
Same comment here, though that inline function below looks highly 
optimized...
> +static inline void *pzalloc(struct gen_pool *pool, size_t size, gfp_t gfp)
> +{
> +	return pmalloc(pool, size, gfp | __GFP_ZERO);
> +}
> +
> +/**
> + * pmalloc_array() - allocates an array according to the parameters
> + * @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
> + * @flags: flags for page allocation
> + *
> + * Executes pmalloc, if it has a chance to succeed.
> + *
> + * Return:
> + * * the pmalloc result	- success
> + * * NULL		- error
> + */
> +static inline void *pmalloc_array(struct gen_pool *pool, size_t n,
> +				  size_t size, gfp_t flags)
> +{
> +	if (unlikely(!(pool && n && size)))
Has this code been run through sparse? I know one thing sparse looks at 
is if NULL is being treated like a 0, and sparse does check cases when 0 
is being used in place for NULL for pointer checks, and I'm wondering if 
that line of code would pass.

> +		return NULL;
> +	return pmalloc(pool, n * size, flags);
> +}
> +
> +/**
> + * pcalloc() - allocates a 0-initialized array according to the parameters
> + * @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
> + * @flags: flags for page allocation
> + *
> + * Executes pmalloc_array, if it has a chance to succeed.
> + *
> + * Return:
> + * * the pmalloc result	- success
> + * * NULL		- error
> + */
> +static inline void *pcalloc(struct gen_pool *pool, size_t n,
> +			    size_t size, gfp_t flags)
> +{
> +	return pmalloc_array(pool, n, size, flags | __GFP_ZERO);
> +}
> +
> +/**
> + * pstrdup() - duplicate a string, using pmalloc as allocator
> + * @pool: handle to the pool to be used for memory allocation
> + * @s: string to duplicate
> + * @gfp: flags for page allocation
> + *
> + * 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 gen_pool *pool, const char *s, gfp_t gfp)
> +{
> +	size_t len;
> +	char *buf;
> +
> +	if (unlikely(pool == NULL || s == NULL))
Here, the right check is being done, so at the very least, I would make 
the last line I commented on the same as this one for code continuity.
> +		return NULL;
> +
> +	len = strlen(s) + 1;
> +	buf = pmalloc(pool, len, gfp);
> +	if (likely(buf))
> +		strncpy(buf, s, len);
> +	return buf;
> +}
> +
> +/**
> + * pmalloc_protect_pool() - turn a read/write pool read-only
> + * @pool: the pool to protect
> + *
> + * Write-protects all the memory chunks assigned to the pool.
> + * This prevents any further allocation.
> + *
> + * Return:
> + * * 0		- success
> + * * -EINVAL	- error
> + */
> +int pmalloc_protect_pool(struct gen_pool *pool);
> +
> +/**
> + * pfree() - mark as unused memory that was previously in use
> + * @pool: handle to the pool to be used for memory allocation
> + * @addr: the beginning of the memory area to be freed
> + *
> + * The behavior of pfree is different, depending on the state of the
> + * protection.
> + * If the pool is not yet protected, the memory is marked as unused and
> + * will be available for further allocations.
> + * If the pool is already protected, the memory is marked as unused, but
> + * it will still be impossible to perform further allocation, because of
> + * the existing protection.
> + * The freed memory, in this case, will be truly released only when the
> + * pool is destroyed.
> + */
> +static inline void pfree(struct gen_pool *pool, const void *addr)
> +{
> +	gen_pool_free(pool, (unsigned long)addr, 0);
> +}
> +
> +/**
> + * pmalloc_destroy_pool() - destroys a pool and all the associated memory
> + * @pool: the pool to destroy
> + *
> + * All the memory that was allocated through pmalloc in the pool will be freed.
> + *
> + * Return:
> + * * 0		- success
> + * * -EINVAL	- error
> + */
> +int pmalloc_destroy_pool(struct gen_pool *pool);
> +
> +#endif
> diff --git a/include/linux/vmalloc.h b/include/linux/vmalloc.h
> index 1e5d8c392f15..116d280cca53 100644
> --- a/include/linux/vmalloc.h
> +++ b/include/linux/vmalloc.h
> @@ -20,6 +20,7 @@ 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 */
>   /* bits [20..32] reserved for arch specific ioremap internals */
>   
>   /*
> diff --git a/lib/genalloc.c b/lib/genalloc.c
> index 87f62f31b52f..24ed35035095 100644
> --- a/lib/genalloc.c
> +++ b/lib/genalloc.c
> @@ -625,6 +625,33 @@ void gen_pool_free(struct gen_pool *pool, unsigned long addr, size_t size)
>   }
>   EXPORT_SYMBOL(gen_pool_free);
>   
> +
> +/**
> + * gen_pool_flush_chunk() - drops all the allocations from a specific chunk
> + * @pool:	the generic memory pool
> + * @chunk:	The chunk to wipe clear.
> + *
> + * This is meant to be called only while destroying a pool. It's up to the
> + * caller to avoid races, but really, at this point the pool should have
> + * already been retired and it should have become unavailable for any other
> + * sort of operation.
> + */
> +void gen_pool_flush_chunk(struct gen_pool *pool,
> +			  struct gen_pool_chunk *chunk)
> +{
> +	size_t size;
> +
> +	if (unlikely(!(pool && chunk)))

Please make this check the same as the last line I commented on, 
especially since it's the same struct being checked.

> +		return;
> +
> +	size = chunk->end_addr + 1 - chunk->start_addr;
> +	memset(chunk->entries, 0,
> +	       DIV_ROUND_UP(size >> pool->min_alloc_order * BITS_PER_ENTRY,
> +			    BITS_PER_BYTE));
> +	atomic_long_set(&chunk->avail, size);
> +}
> +
> +
>   /**
>    * gen_pool_for_each_chunk() - call func for every chunk of generic memory pool
>    * @pool:	the generic memory pool
> diff --git a/mm/Kconfig b/mm/Kconfig
> index c782e8fb7235..be578fbdce6d 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 ARCH_HAS_SET_MEMORY
> +    select GENERIC_ALLOCATOR
> +    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..abddba90a9f6
> --- /dev/null
> +++ b/mm/pmalloc.c
> @@ -0,0 +1,499 @@
> +// SPDX-License-Identifier: GPL-2.0
> +/*
> + * pmalloc.c: Protectable Memory Allocator
> + *
> + * (C) Copyright 2017 Huawei Technologies Co. Ltd.
> + * Author: Igor Stoppa <igor.stoppa@xxxxxxxxxx>
> + */
> +
> +#include <linux/printk.h>
> +#include <linux/init.h>
> +#include <linux/mm.h>
> +#include <linux/vmalloc.h>
> +#include <linux/genalloc.h>
> +#include <linux/kernel.h>
> +#include <linux/log2.h>
> +#include <linux/slab.h>
> +#include <linux/device.h>
> +#include <linux/atomic.h>
> +#include <linux/rculist.h>
> +#include <linux/set_memory.h>
> +#include <asm/cacheflush.h>
> +#include <asm/page.h>
> +
> +#include <linux/pmalloc.h>
> +/*
> + * pmalloc_data contains the data specific to a pmalloc pool,
> + * in a format compatible with the design of gen_alloc.
> + * Some of the fields are used for exposing the corresponding parameter
> + * to userspace, through sysfs.
> + */
> +struct pmalloc_data {
> +	struct gen_pool *pool;  /* Link back to the associated pool. */
> +	bool protected;     /* Status of the pool: RO or RW. */
> +	struct kobj_attribute attr_protected; /* Sysfs attribute. */
> +	struct kobj_attribute attr_avail;     /* Sysfs attribute. */
> +	struct kobj_attribute attr_size;      /* Sysfs attribute. */
> +	struct kobj_attribute attr_chunks;    /* Sysfs attribute. */
> +	struct kobject *pool_kobject;
> +	struct list_head node; /* list of pools */
> +};
> +
> +static LIST_HEAD(pmalloc_final_list);
> +static LIST_HEAD(pmalloc_tmp_list);
> +static struct list_head *pmalloc_list = &pmalloc_tmp_list;
> +static DEFINE_MUTEX(pmalloc_mutex);
> +static struct kobject *pmalloc_kobject;
> +
> +static ssize_t pmalloc_pool_show_protected(struct kobject *dev,
> +					   struct kobj_attribute *attr,
> +					   char *buf)
> +{
> +	struct pmalloc_data *data;
> +
> +	data = container_of(attr, struct pmalloc_data, attr_protected);
> +	if (data->protected)
> +		return sprintf(buf, "protected\n");
> +	else
> +		return sprintf(buf, "unprotected\n");
> +}
> +
> +static ssize_t pmalloc_pool_show_avail(struct kobject *dev,
> +				       struct kobj_attribute *attr,
> +				       char *buf)
> +{
> +	struct pmalloc_data *data;
> +
> +	data = container_of(attr, struct pmalloc_data, attr_avail);
> +	return sprintf(buf, "%lu\n",
> +		       (unsigned long)gen_pool_avail(data->pool));
> +}
> +
> +static ssize_t pmalloc_pool_show_size(struct kobject *dev,
> +				      struct kobj_attribute *attr,
> +				      char *buf)
> +{
> +	struct pmalloc_data *data;
> +
> +	data = container_of(attr, struct pmalloc_data, attr_size);
> +	return sprintf(buf, "%lu\n",
> +		       (unsigned long)gen_pool_size(data->pool));
> +}
> +
> +static void pool_chunk_number(struct gen_pool *pool,
> +			      struct gen_pool_chunk *chunk, void *data)
> +{
> +	unsigned long *counter = data;
> +
> +	(*counter)++;
> +}
> +
> +static ssize_t pmalloc_pool_show_chunks(struct kobject *dev,
> +					struct kobj_attribute *attr,
> +					char *buf)
> +{
> +	struct pmalloc_data *data;
> +	unsigned long chunks_num = 0;
> +
> +	data = container_of(attr, struct pmalloc_data, attr_chunks);
> +	gen_pool_for_each_chunk(data->pool, pool_chunk_number, &chunks_num);
> +	return sprintf(buf, "%lu\n", chunks_num);
> +}
> +
> +/* Exposes the pool and its attributes through sysfs. */
> +static struct kobject *pmalloc_connect(struct pmalloc_data *data)
> +{
> +	const struct attribute *attrs[] = {
> +		&data->attr_protected.attr,
> +		&data->attr_avail.attr,
> +		&data->attr_size.attr,
> +		&data->attr_chunks.attr,
> +		NULL
> +	};
> +	struct kobject *kobj;
> +
> +	kobj = kobject_create_and_add(data->pool->name, pmalloc_kobject);
> +	if (unlikely(!kobj))
> +		return NULL;
> +
> +	if (unlikely(sysfs_create_files(kobj, attrs) < 0)) {
> +		kobject_put(kobj);
> +		kobj = NULL;
> +	}
> +	return kobj;
> +}
> +
> +/* Removes the pool and its attributes from sysfs. */
> +static void pmalloc_disconnect(struct pmalloc_data *data,
> +			       struct kobject *kobj)
> +{
> +	const struct attribute *attrs[] = {
> +		&data->attr_protected.attr,
> +		&data->attr_avail.attr,
> +		&data->attr_size.attr,
> +		&data->attr_chunks.attr,
> +		NULL
> +	};
> +
> +	sysfs_remove_files(kobj, attrs);
> +	kobject_put(kobj);
> +}
> +
> +/* Declares an attribute of the pool. */
> +#define pmalloc_attr_init(data, attr_name) \
> +do { \
> +	sysfs_attr_init(&data->attr_##attr_name.attr); \
> +	data->attr_##attr_name.attr.name = #attr_name; \
> +	data->attr_##attr_name.attr.mode = VERIFY_OCTAL_PERMISSIONS(0400); \
> +	data->attr_##attr_name.show = pmalloc_pool_show_##attr_name; \
> +} while (0)
> +
> +struct gen_pool *pmalloc_create_pool(const char *name, int min_alloc_order)
> +{
> +	struct gen_pool *pool;
> +	const char *pool_name;
> +	struct pmalloc_data *data;
> +
> +	if (!name) {
> +		WARN_ON(1);
?? Maybe the name check should be in WARN_ON()?
> +		return NULL;
> +	}
> +
> +	if (min_alloc_order < 0)
> +		min_alloc_order = ilog2(sizeof(unsigned long));
> +
> +	pool = gen_pool_create(min_alloc_order, NUMA_NO_NODE);
> +	if (unlikely(!pool))
> +		return NULL;
> +
> +	mutex_lock(&pmalloc_mutex);
> +	list_for_each_entry(data, pmalloc_list, node)
> +		if (!strcmp(name, data->pool->name))
> +			goto same_name_err;
> +
> +	pool_name = kstrdup(name, GFP_KERNEL);
> +	if (unlikely(!pool_name))
> +		goto name_alloc_err;
> +
> +	data = kzalloc(sizeof(struct pmalloc_data), GFP_KERNEL);
> +	if (unlikely(!data))
> +		goto data_alloc_err;
> +
> +	data->protected = false;
> +	data->pool = pool;
> +	pmalloc_attr_init(data, protected);
> +	pmalloc_attr_init(data, avail);
> +	pmalloc_attr_init(data, size);
> +	pmalloc_attr_init(data, chunks);
> +	pool->data = data;
> +	pool->name = pool_name;
> +
> +	list_add(&data->node, pmalloc_list);
> +	if (pmalloc_list == &pmalloc_final_list)
> +		data->pool_kobject = pmalloc_connect(data);
> +	mutex_unlock(&pmalloc_mutex);
> +	return pool;
> +
> +data_alloc_err:
> +	kfree(pool_name);
> +name_alloc_err:
> +same_name_err:
> +	mutex_unlock(&pmalloc_mutex);
> +	gen_pool_destroy(pool);
> +	return NULL;
> +}
> +
> +static inline int check_alloc_params(struct gen_pool *pool, size_t req_size)
> +{
> +	struct pmalloc_data *data;
> +
> +	if (unlikely(!req_size || !pool))
same unlikely() check problem mentioned before.
> +		return -1;
Can we use an errno value instead for better diagnosibility?
> +
> +	data = pool->data;
> +
> +	if (data == NULL)
> +		return -1;
Same here (ENOMEM or ENXIO comes to mind).
> +
> +	if (unlikely(data->protected)) {
> +		WARN_ON(1);
Maybe re-write this with the check inside WARN_ON()?
> +		return -1;

Same here, how about a different errno value for this case?
> +	}
> +	return 0;
> +}
> +
> +
> +static inline bool chunk_tagging(void *chunk, bool tag)
> +{
> +	struct vm_struct *area;
> +	struct page *page;
> +
> +	if (!is_vmalloc_addr(chunk))
> +		return false;
> +
> +	page = vmalloc_to_page(chunk);
> +	if (unlikely(!page))
> +		return false;
> +
> +	area = page->area;
> +	if (tag)
> +		area->flags |= VM_PMALLOC;
> +	else
> +		area->flags &= ~VM_PMALLOC;
> +	return true;
> +}
> +
> +
> +static inline bool tag_chunk(void *chunk)
> +{
> +	return chunk_tagging(chunk, true);
> +}
> +
> +
> +static inline bool untag_chunk(void *chunk)
> +{
> +	return chunk_tagging(chunk, false);
> +}
> +
> +enum {
> +	INVALID_PMALLOC_OBJECT = -1,
> +	NOT_PMALLOC_OBJECT = 0,
> +	VALID_PMALLOC_OBJECT = 1,
> +};
> +
> +int is_pmalloc_object(const void *ptr, const unsigned long n)
> +{
> +	struct vm_struct *area;
> +	struct page *page;
> +	unsigned long area_start;
> +	unsigned long area_end;
> +	unsigned long object_start;
> +	unsigned long object_end;
> +
> +
> +	/*
> +	 * is_pmalloc_object gets called pretty late, so chances are high
> +	 * that the object is indeed of vmalloc type
> +	 */
> +	if (unlikely(!is_vmalloc_addr(ptr)))
> +		return NOT_PMALLOC_OBJECT;
> +
> +	page = vmalloc_to_page(ptr);
> +	if (unlikely(!page))
> +		return NOT_PMALLOC_OBJECT;
> +
> +	area = page->area;
> +
> +	if (likely(!(area->flags & VM_PMALLOC)))
> +		return NOT_PMALLOC_OBJECT;
> +
> +	area_start = (unsigned long)area->addr;
> +	area_end = area_start + area->nr_pages * PAGE_SIZE - 1;
> +	object_start = (unsigned long)ptr;
> +	object_end = object_start + n - 1;
> +
> +	if (likely((area_start <= object_start) &&
> +		   (object_end <= area_end)))
> +		return VALID_PMALLOC_OBJECT;
> +	else
> +		return INVALID_PMALLOC_OBJECT;
> +}
> +
> +
> +bool pmalloc_prealloc(struct gen_pool *pool, size_t size)
> +{
> +	void *chunk;
> +	size_t chunk_size;
> +	bool add_error;
> +
> +	if (check_alloc_params(pool, size))
> +		return false;
> +
> +	/* Expand pool */
> +	chunk_size = roundup(size, PAGE_SIZE);
> +	chunk = vmalloc(chunk_size);
> +	if (unlikely(chunk == NULL))
> +		return false;
> +
> +	/* Locking is already done inside gen_pool_add */
> +	add_error = gen_pool_add(pool, (unsigned long)chunk, chunk_size,
> +				 NUMA_NO_NODE);
> +	if (unlikely(add_error != 0))
> +		goto abort;
> +
> +	return true;
> +abort:
> +	vfree_atomic(chunk);
> +	return false;
> +
> +}
> +
> +void *pmalloc(struct gen_pool *pool, size_t size, gfp_t gfp)
> +{
> +	void *chunk;
> +	size_t chunk_size;
> +	bool add_error;
> +	unsigned long retval;
> +
> +	if (check_alloc_params(pool, size))
> +		return NULL;
> +
> +retry_alloc_from_pool:
> +	retval = gen_pool_alloc(pool, size);
> +	if (retval)
> +		goto return_allocation;
> +
> +	if (unlikely((gfp & __GFP_ATOMIC))) {
> +		if (unlikely((gfp & __GFP_NOFAIL)))
> +			goto retry_alloc_from_pool;
> +		else
> +			return NULL;
> +	}
> +
> +	/* Expand pool */
> +	chunk_size = roundup(size, PAGE_SIZE);
> +	chunk = vmalloc(chunk_size);
> +	if (unlikely(!chunk)) {
> +		if (unlikely((gfp & __GFP_NOFAIL)))
> +			goto retry_alloc_from_pool;
> +		else
> +			return NULL;
> +	}
> +	if (unlikely(!tag_chunk(chunk)))
> +		goto free;
> +
> +	/* Locking is already done inside gen_pool_add */
> +	add_error = gen_pool_add(pool, (unsigned long)chunk, chunk_size,
> +				 NUMA_NO_NODE);
> +	if (unlikely(add_error))
> +		goto abort;
> +
> +	retval = gen_pool_alloc(pool, size);
> +	if (retval) {
> +return_allocation:
> +		*(size_t *)retval = size;
> +		if (gfp & __GFP_ZERO)
> +			memset((void *)retval, 0, size);
> +		return (void *)retval;
> +	}
> +	/*
> +	 * Here there is no test for __GFP_NO_FAIL because, in case of
> +	 * concurrent allocation, one thread might add a chunk to the
> +	 * pool and this memory could be allocated by another thread,
> +	 * before the first thread gets a chance to use it.
> +	 * As long as vmalloc succeeds, it's ok to retry.
> +	 */
> +	goto retry_alloc_from_pool;
> +abort:
> +	untag_chunk(chunk);
> +free:
> +	vfree_atomic(chunk);
> +	return NULL;
> +}
> +
> +static void pmalloc_chunk_set_protection(struct gen_pool *pool,
> +
> +					 struct gen_pool_chunk *chunk,
> +					 void *data)
> +{
> +	const bool *flag = data;
> +	size_t chunk_size = chunk->end_addr + 1 - chunk->start_addr;
> +	unsigned long pages = chunk_size / PAGE_SIZE;
> +
> +	BUG_ON(chunk_size & (PAGE_SIZE - 1));
Re-think WARN_ON() for BUG_ON()? And also check chunk as well, as it's 
being used below?
> +
> +	if (*flag)
> +		set_memory_ro(chunk->start_addr, pages);
> +	else
> +		set_memory_rw(chunk->start_addr, pages);
> +}
> +
> +static int pmalloc_pool_set_protection(struct gen_pool *pool, bool protection)
> +{
> +	struct pmalloc_data *data;
> +	struct gen_pool_chunk *chunk;
> +
> +	if (unlikely(!pool))
> +		return -EINVAL;
This is example of what I'd perfer seeing in check_alloc_params().
> +
> +	data = pool->data;
> +
> +	if (unlikely(!data))
> +		return -EINVAL;
ENXIO or EIO or ENOMEM sound better?
> +
> +	if (unlikely(data->protected == protection)) {
> +		WARN_ON(1);
Better to put the check inside WARN_ON, me thinks...
> +		return 0;
> +	}
> +
> +	data->protected = protection;
> +	list_for_each_entry(chunk, &(pool)->chunks, next_chunk)
> +		pmalloc_chunk_set_protection(pool, chunk, &protection);
> +	return 0;
> +}
> +
> +int pmalloc_protect_pool(struct gen_pool *pool)
> +{
> +	return pmalloc_pool_set_protection(pool, true);
Is pool == NULL being checked somewhere, similar to previous functions 
in this patch?
> +}
> +
> +
> +static void pmalloc_chunk_free(struct gen_pool *pool,
> +			       struct gen_pool_chunk *chunk, void *data)
> +{
Wat is 'data' being used for? Looks unused. Should parameters be 
checked, like other ones?
> +	untag_chunk(chunk);
> +	gen_pool_flush_chunk(pool, chunk);
> +	vfree_atomic((void *)chunk->start_addr);
> +}
> +
> +
> +int pmalloc_destroy_pool(struct gen_pool *pool)
> +{
> +	struct pmalloc_data *data;
> +
> +	if (unlikely(pool == NULL))
> +		return -EINVAL;
> +
> +	data = pool->data;
> +
> +	if (unlikely(data == NULL))
> +		return -EINVAL;

I'd use a different errno value since you already used it for pool.
> +
> +	mutex_lock(&pmalloc_mutex);
> +	list_del(&data->node);
> +	mutex_unlock(&pmalloc_mutex);
> +
> +	if (likely(data->pool_kobject))
> +		pmalloc_disconnect(data, data->pool_kobject);
> +
> +	pmalloc_pool_set_protection(pool, false);
> +	gen_pool_for_each_chunk(pool, pmalloc_chunk_free, NULL);
> +	gen_pool_destroy(pool);
> +	kfree(data);
Does data need to be set to NULL in this case, as data is a member of 
pool (pool->data)? I'm worried about dangling pointer scenarios which 
probably isn't good for security modules?
> +	return 0;
> +}
> +
> +/*
> + * When the sysfs is ready to receive registrations, connect all the
> + * pools previously created. Also enable further pools to be connected
> + * right away.
> + */
> +static int __init pmalloc_late_init(void)
> +{
> +	struct pmalloc_data *data, *n;
> +
> +	pmalloc_kobject = kobject_create_and_add("pmalloc", kernel_kobj);
> +
> +	mutex_lock(&pmalloc_mutex);
> +	pmalloc_list = &pmalloc_final_list;
> +
> +	if (likely(pmalloc_kobject != NULL)) {
> +		list_for_each_entry_safe(data, n, &pmalloc_tmp_list, node) {
> +			list_move(&data->node, &pmalloc_final_list);
> +			pmalloc_connect(data);
> +		}
> +	}
It would be nice to have the init() return an error value in case of 
failure.

Thanks,
Jay