Introduce type-aware kmalloc-family helpers to replace the common idioms for single, array, and flexible object allocations: ptr = kmalloc(sizeof(*ptr), gfp); ptr = kzalloc(sizeof(*ptr), gfp); ptr = kmalloc_array(count, sizeof(*ptr), gfp); ptr = kcalloc(count, sizeof(*ptr), gfp); ptr = kmalloc(struct_size(ptr, flex_member, count), gfp); These become, respectively: kmalloc_obj(ptr, gfp); kzalloc_obj(ptr, gfp); kmalloc_objs(ptr, count, gfp); kzalloc_objs(ptr, count, gfp); kmalloc_flex(ptr, flex_member, count, gfp); These each return the assigned value of ptr (which may be NULL on failure). For cases where the total size of the allocation is needed, the kmalloc_obj_sz(), kmalloc_objs_sz(), and kmalloc_flex_sz() family of macros can be used. For example: info->size = struct_size(ptr, flex_member, count); ptr = kmalloc(info->size, gfp); becomes: kmalloc_flex_sz(ptr, flex_member, count, gfp, &info->size); Internal introspection of allocated type now becomes possible, allowing for future alignment-aware choices and hardening work. For example, adding __alignof(*ptr) as an argument to the internal allocators so that appropriate/efficient alignment choices can be made, or being able to correctly choose per-allocation offset randomization within a bucket that does not break alignment requirements. Introduces __flex_count() for when __builtin_get_counted_by() is added by GCC[1] and Clang[2]. The internal use of __flex_count() allows for automatically setting the counter member of a struct's flexible array member when it has been annotated with __counted_by(), avoiding any missed early size initializations while __counted_by() annotations are added to the kernel. Additionally, this also checks for "too large" allocations based on the type size of the counter variable. For example: if (count > type_max(ptr->flex_count)) fail...; info->size = struct_size(ptr, flex_member, count); ptr = kmalloc(info->size, gfp); ptr->flex_count = count; becomes (i.e. unchanged from earlier example): kmalloc_flex_sz(ptr, flex_member, count, gfp, &info->size); Replacing all existing simple code patterns found via Coccinelle[3] shows what could be replaced immediately (saving roughly 1,500 lines): 7040 files changed, 14128 insertions(+), 15557 deletions(-) Link: https://gcc.gnu.org/bugzilla/show_bug.cgi?id=116016 [1] Link: https://github.com/llvm/llvm-project/issues/99774 [2] Link: https://github.com/kees/kernel-tools/blob/trunk/coccinelle/examples/kmalloc_obj-assign-size.cocci [3] Signed-off-by: Kees Cook <kees@xxxxxxxxxx> --- Initial testing looks good. Before I write all the self-tests, I just wanted to validate that the new API is reasonable (i.e. it is no longer using optional argument counts for choosing the internal API). v3: - Add .rst documentation - Add kern-doc - Return ptr instead of size by default - Add *_sz() variants that provide allocation size output - Implement __flex_counter() logic v2: https://lore.kernel.org/linux-hardening/20240807235433.work.317-kees@xxxxxxxxxx/ v1: https://lore.kernel.org/linux-hardening/20240719192744.work.264-kees@xxxxxxxxxx/ Cc: Vlastimil Babka <vbabka@xxxxxxx> Cc: Christoph Lameter <cl@xxxxxxxxx> Cc: Pekka Enberg <penberg@xxxxxxxxxx> Cc: David Rientjes <rientjes@xxxxxxxxxx> Cc: Joonsoo Kim <iamjoonsoo.kim@xxxxxxx> Cc: Andrew Morton <akpm@xxxxxxxxxxxxxxxxxxxx> Cc: Roman Gushchin <roman.gushchin@xxxxxxxxx> Cc: Hyeonggon Yoo <42.hyeyoo@xxxxxxxxx> Cc: Gustavo A. R. Silva <gustavoars@xxxxxxxxxx> Cc: Bill Wendling <morbo@xxxxxxxxxx> Cc: Justin Stitt <justinstitt@xxxxxxxxxx> Cc: Jann Horn <jannh@xxxxxxxxxx> Cc: Przemek Kitszel <przemyslaw.kitszel@xxxxxxxxx> Cc: Marco Elver <elver@xxxxxxxxxx> Cc: linux-mm@xxxxxxxxx --- Documentation/process/deprecated.rst | 41 +++++++ include/linux/compiler_types.h | 22 ++++ include/linux/slab.h | 174 +++++++++++++++++++++++++++ 3 files changed, 237 insertions(+) diff --git a/Documentation/process/deprecated.rst b/Documentation/process/deprecated.rst index 1f7f3e6c9cda..b22ec088a044 100644 --- a/Documentation/process/deprecated.rst +++ b/Documentation/process/deprecated.rst @@ -372,3 +372,44 @@ The helper must be used:: DECLARE_FLEX_ARRAY(struct type2, two); }; }; + +Open-coded kmalloc assignments +------------------------------ +Performing open-coded kmalloc()-family allocation assignments prevents +the kernel (and compiler) from being able to examine the type of the +variable being assigned, which limits any related introspection that +may help with alignment, wrap-around, or additional hardening. The +kmalloc_obj()-family of macros provide this introspection, which can be +used for the common code patterns for single, array, and flexible object +allocations. For example, these open coded assignments:: + + ptr = kmalloc(sizeof(*ptr), gfp); + ptr = kzalloc(sizeof(*ptr), gfp); + ptr = kmalloc_array(count, sizeof(*ptr), gfp); + ptr = kcalloc(count, sizeof(*ptr), gfp); + ptr = kmalloc(struct_size(ptr, flex_member, count), gfp); + +become, respectively:: + + kmalloc_obj(ptr, gfp); + kzalloc_obj(ptr, gfp); + kmalloc_objs(ptr, count, gfp); + kzalloc_objs(ptr, count, gfp); + kmalloc_flex(ptr, flex_member, count, gfp); + +For the cases where the total size of the allocation is also needed, +the kmalloc_obj_size(), kmalloc_objs_sz(), and kmalloc_flex_sz() family of +macros can be used. For example, converting these assignments:: + + total_size = struct_size(ptr, flex_member, count); + ptr = kmalloc(total_size, gfp); + +becomes:: + + kmalloc_flex_sz(ptr, flex_member, count, gfp, &total_size); + +If `ptr->flex_member` is annotated with __counted_by(), the allocation +will automatically fail if `count` is larger than the maximum +representable value that can be stored in the counter member associated +with `flex_member`. Similarly, the allocation will fail if the total +size of the allocation exceeds the maximum value `*total_size` can hold. diff --git a/include/linux/compiler_types.h b/include/linux/compiler_types.h index f14c275950b5..b99deae45210 100644 --- a/include/linux/compiler_types.h +++ b/include/linux/compiler_types.h @@ -421,6 +421,28 @@ struct ftrace_likely_data { #define __member_size(p) __builtin_object_size(p, 1) #endif +#if __has_builtin(__builtin_get_counted_by) +/** + * __flex_counter - Get pointer to counter member for the given + * flexible array, if it was annotated with __counted_by() + * @flex: Pointer to flexible array member of an addressable struct instance + * + * For example, with: + * + * struct foo { + * int counter; + * short array[] __counted_by(counter); + * } *p; + * + * __flex_counter(p->array) will resolve to &p->counter. + * + * If p->array is unannotated, this returns (void *)NULL. + */ +#define __flex_counter(flex) __builtin_get_counted_by(flex) +#else +#define __flex_counter(flex) ((void *)NULL) +#endif + /* * Some versions of gcc do not mark 'asm goto' volatile: * diff --git a/include/linux/slab.h b/include/linux/slab.h index eb2bf4629157..c37606b9e248 100644 --- a/include/linux/slab.h +++ b/include/linux/slab.h @@ -686,6 +686,180 @@ static __always_inline __alloc_size(1) void *kmalloc_noprof(size_t size, gfp_t f } #define kmalloc(...) alloc_hooks(kmalloc_noprof(__VA_ARGS__)) +#define __alloc_objs(ALLOC, P, COUNT, FLAGS, SIZE) \ +({ \ + size_t __obj_size = size_mul(sizeof(*P), COUNT); \ + const typeof(_Generic(SIZE, \ + void *: (size_t *)NULL, \ + default: SIZE)) __size_ptr = (SIZE); \ + typeof(P) __obj_ptr = NULL; \ + /* Does the total size fit in the *SIZE variable? */ \ + if (!__size_ptr || __obj_size <= type_max(*__size_ptr)) \ + __obj_ptr = ALLOC(__obj_size, FLAGS); \ + if (!__obj_ptr) \ + __obj_size = 0; \ + if (__size_ptr) \ + *__size_ptr = __obj_size; \ + (P) = __obj_ptr; \ +}) + +#define __alloc_flex(ALLOC, P, FAM, COUNT, FLAGS, SIZE) \ +({ \ + size_t __count = (COUNT); \ + size_t __obj_size = struct_size(P, FAM, __count); \ + const typeof(_Generic(SIZE, \ + void *: (size_t *)NULL, \ + default: SIZE)) __size_ptr = (SIZE); \ + typeof(P) __obj_ptr = NULL; \ + /* Just query the counter type for type_max checking. */ \ + typeof(_Generic(__flex_counter(__obj_ptr->FAM), \ + void *: (size_t *)NULL, \ + default: __flex_counter(__obj_ptr->FAM))) \ + __counter_type_ptr = NULL; \ + /* Does the count fit in the __counted_by counter member? */ \ + if ((__count <= type_max(*__counter_type_ptr)) && \ + /* Does the total size fit in the *SIZE variable? */ \ + (!__size_ptr || __obj_size <= type_max(*__size_ptr))) \ + __obj_ptr = ALLOC(__obj_size, FLAGS); \ + if (__obj_ptr) { \ + /* __obj_ptr now allocated so get real counter ptr. */ \ + typeof(_Generic(__flex_counter(__obj_ptr->FAM), \ + void *: (size_t *)NULL, \ + default: __flex_counter(__obj_ptr->FAM))) \ + __counter_ptr = __flex_counter(__obj_ptr->FAM); \ + if (__counter_ptr) \ + *__counter_ptr = __count; \ + } else { \ + __obj_size = 0; \ + } \ + if (__size_ptr) \ + *__size_ptr = __obj_size; \ + (P) = __obj_ptr; \ +}) + +/** + * kmalloc_obj - Allocate a single instance of the given structure + * @P: Pointer to hold allocation of the structure + * @FLAGS: GFP flags for the allocation + * + * Returns the newly allocated value of @P on success, NULL on failure. + * @P is assigned the result, either way. + */ +#define kmalloc_obj(P, FLAGS) \ + __alloc_objs(kmalloc, P, 1, FLAGS, NULL) +/** + * kmalloc_obj_sz - Allocate a single instance of the given structure and + * store total size + * @P: Pointer to hold allocation of the structure + * @FLAGS: GFP flags for the allocation + * @SIZE: Pointer to variable to hold the total allocation size + * + * Returns the newly allocated value of @P on success, NULL on failure. + * @P is assigned the result, either way. If @SIZE is non-NULL, the + * allocation will immediately fail if the total allocation size is larger + * than what the type of *@SIZE can represent. + */ +#define kmalloc_obj_sz(P, FLAGS, SIZE) \ + __alloc_objs(kmalloc, P, 1, FLAGS, SIZE) +/** + * kmalloc_objs - Allocate an array of the given structure + * @P: Pointer to hold allocation of the structure array + * @COUNT: How many elements in the array + * @FLAGS: GFP flags for the allocation + * + * Returns the newly allocated value of @P on success, NULL on failure. + * @P is assigned the result, either way. + */ +#define kmalloc_objs(P, COUNT, FLAGS) \ + __alloc_objs(kmalloc, P, COUNT, FLAGS, NULL) +/** + * kmalloc_objs_sz - Allocate an array of the given structure and store + * total size + * @P: Pointer to hold allocation of the structure array + * @COUNT: How many elements in the array + * @FLAGS: GFP flags for the allocation + * @SIZE: Pointer to variable to hold the total allocation size + * + * Returns the newly allocated value of @P on success, NULL on failure. + * @P is assigned the result, either way. If @SIZE is non-NULL, the + * allocation will immediately fail if the total allocation size is larger + * than what the type of *@SIZE can represent. + */ +#define kmalloc_objs_sz(P, COUNT, FLAGS, SIZE) \ + __alloc_objs(kmalloc, P, COUNT, FLAGS, SIZE) +/** + * kmalloc_flex - Allocate a single instance of the given flexible structure + * @P: Pointer to hold allocation of the structure + * @FAM: The name of the flexible array member of the structure + * @COUNT: How many flexible array member elements are desired + * @FLAGS: GFP flags for the allocation + * + * Returns the newly allocated value of @P on success, NULL on failure. + * @P is assigned the result, either way. If @FAM has been annotated with + * __counted_by(), the allocation will immediately fail if @COUNT is larger + * than what the type of the struct's counter variable can represent. + */ +#define kmalloc_flex(P, FAM, COUNT, FLAGS) \ + __alloc_flex(kmalloc, P, FAM, COUNT, FLAGS, NULL) + +/** + * kmalloc_flex_sz - Allocate a single instance of the given flexible + * structure and store total size + * @P: Pointer to hold allocation of the structure + * @FAM: The name of the flexible array member of the structure + * @COUNT: How many flexible array member elements are desired + * @FLAGS: GFP flags for the allocation + * @SIZE: Pointer to variable to hold the total allocation size + * + * Returns the newly allocated value of @P on success, NULL on failure. + * @P is assigned the result, either way. If @FAM has been annotated with + * __counted_by(), the allocation will immediately fail if @COUNT is larger + * than what the type of the struct's counter variable can represent. If + * @SIZE is non-NULL, the allocation will immediately fail if the total + * allocation size is larger than what the type of *@SIZE can represent. + */ +#define kmalloc_flex_sz(P, FAM, COUNT, FLAGS, SIZE) \ + __alloc_flex(kmalloc, P, FAM, COUNT, FLAGS, SIZE) + +#define kzalloc_obj(P, FLAGS) \ + __alloc_objs(kzalloc, P, 1, FLAGS, NULL) +#define kzalloc_obj_sz(P, FLAGS, SIZE) \ + __alloc_objs(kzalloc, P, 1, FLAGS, SIZE) +#define kzalloc_objs(P, COUNT, FLAGS) \ + __alloc_objs(kzalloc, P, COUNT, FLAGS, NULL) +#define kzalloc_objs_sz(P, COUNT, FLAGS, SIZE) \ + __alloc_objs(kzalloc, P, COUNT, FLAGS, SIZE) +#define kzalloc_flex(P, FAM, COUNT, FLAGS) \ + __alloc_flex(kzalloc, P, FAM, COUNT, FLAGS, NULL) +#define kzalloc_flex_sz(P, FAM, COUNT, FLAGS, SIZE) \ + __alloc_flex(kzalloc, P, FAM, COUNT, FLAGS, SIZE) + +#define kvmalloc_obj(P, FLAGS) \ + __alloc_objs(kvmalloc, P, 1, FLAGS, NULL) +#define kvmalloc_obj_sz(P, FLAGS, SIZE) \ + __alloc_objs(kvmalloc, P, 1, FLAGS, SIZE) +#define kvmalloc_objs(P, COUNT, FLAGS) \ + __alloc_objs(kvmalloc, P, COUNT, FLAGS, NULL) +#define kvmalloc_objs_sz(P, COUNT, FLAGS, SIZE) \ + __alloc_objs(kvmalloc, P, COUNT, FLAGS, SIZE) +#define kvmalloc_flex(P, FAM, COUNT, FLAGS) \ + __alloc_flex(kvmalloc, P, FAM, COUNT, FLAGS, NULL) +#define kvmalloc_flex_sz(P, FAM, COUNT, FLAGS, SIZE) \ + __alloc_flex(kvmalloc, P, FAM, COUNT, FLAGS, SIZE) + +#define kvzalloc_obj(P, FLAGS) \ + __alloc_objs(kvzalloc, P, 1, FLAGS, NULL) +#define kvzalloc_obj_sz(P, FLAGS, SIZE) \ + __alloc_objs(kvzalloc, P, 1, FLAGS, SIZE) +#define kvzalloc_objs(P, COUNT, FLAGS) \ + __alloc_objs(kvzalloc, P, COUNT, FLAGS, NULL) +#define kvzalloc_objs_sz(P, COUNT, FLAGS, SIZE) \ + __alloc_objs(kvzalloc, P, COUNT, FLAGS, SIZE) +#define kvzalloc_flex(P, FAM, COUNT, FLAGS) \ + __alloc_flex(kvzalloc, P, FAM, COUNT, FLAGS, NULL) +#define kvzalloc_flex_sz(P, FAM, COUNT, FLAGS, SIZE) \ + __alloc_flex(kvzalloc, P, FAM, COUNT, FLAGS, SIZE) + #define kmem_buckets_alloc(_b, _size, _flags) \ alloc_hooks(__kmalloc_node_noprof(PASS_BUCKET_PARAMS(_size, _b), _flags, NUMA_NO_NODE)) -- 2.34.1
