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Diffstat (limited to 'Documentation/process/deprecated.rst')
| -rw-r--r-- | Documentation/process/deprecated.rst | 31 |
1 files changed, 31 insertions, 0 deletions
diff --git a/Documentation/process/deprecated.rst b/Documentation/process/deprecated.rst index 1f7f3e6c9cda..fed56864d036 100644 --- a/Documentation/process/deprecated.rst +++ b/Documentation/process/deprecated.rst @@ -372,3 +372,34 @@ The helper must be used:: DECLARE_FLEX_ARRAY(struct type2, two); }; }; + +Open-coded kmalloc assignments for struct objects +------------------------------------------------- +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); + ptr = kmalloc(sizeof(struct foo, gfp); + +become, respectively:: + + ptr = kmalloc_obj(*ptr, gfp); + ptr = kzalloc_obj(*ptr, gfp); + ptr = kmalloc_objs(*ptr, count, gfp); + ptr = kzalloc_objs(*ptr, count, gfp); + ptr = kmalloc_flex(*ptr, flex_member, count, gfp); + __auto_type ptr = kmalloc_obj(struct foo, gfp); + +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`. |