| Message ID | 20240228204919.3680786-3-andriy.shevchenko@linux.intel.com (mailing list archive) |
|---|---|
| State | Not Applicable |
| Headers | show |
| Series | iio: core: New macros and making use of them | expand |
On Wed, Feb 28, 2024 at 10:41:32PM +0200, Andy Shevchenko wrote: > Introduce two helper macros to calculate the size of the structure > with trailing aligned data and to retrieve the pointer to that data. > > Signed-off-by: Andy Shevchenko <andriy.shevchenko@linux.intel.com> > --- > include/linux/overflow.h | 27 ++++++++++++++++++++++++++- > 1 file changed, 26 insertions(+), 1 deletion(-) > > diff --git a/include/linux/overflow.h b/include/linux/overflow.h > index bc390f026128..b93bbf1b6aaa 100644 > --- a/include/linux/overflow.h > +++ b/include/linux/overflow.h > @@ -2,9 +2,10 @@ > #ifndef __LINUX_OVERFLOW_H > #define __LINUX_OVERFLOW_H > > +#include <linux/align.h> > #include <linux/compiler.h> > -#include <linux/limits.h> > #include <linux/const.h> > +#include <linux/limits.h> > > /* > * We need to compute the minimum and maximum values representable in a given > @@ -337,6 +338,30 @@ static inline size_t __must_check size_sub(size_t minuend, size_t subtrahend) > */ > #define array3_size(a, b, c) size_mul(size_mul(a, b), c) > > +/** > + * struct_size_with_data() - Calculate size of structure with trailing aligned data. > + * @p: Pointer to the structure. > + * @a: Alignment in bytes before trailing data. > + * @s: Data size in bytes (must not be 0). > + * > + * Calculates size of memory needed for structure of @p followed by an > + * aligned data of size @s. > + * > + * Return: number of bytes needed or SIZE_MAX on overflow. > + */ > +#define struct_size_with_data(p, a, s) size_add(ALIGN(sizeof(*(p)), (a)), (s)) I don't like this -- "p" should have a trailing flexible array. (See below.) > + > +/** > + * struct_data_pointer - Calculate offset of the trailing data reserved with > + * struct_size_with_data(). > + * @p: Pointer to the structure. > + * @a: Alignment in bytes before trailing data. > + * > + * Return: offset in bytes to the trailing data reserved with > + * struct_size_with_data(). > + */ > +#define struct_data_pointer(p, a) PTR_ALIGN((void *)((p) + 1), (a)) I'm not super excited about propagating the "p + 1" code pattern to find things after an allocation. This leads to the compiler either being blind to accesses beyond an allocation, or being too conservative about accesses beyond an object. Instead of these helpers I would much prefer that data structures that use this code pattern be converted to using trailing flexible arrays, at which point the compiler is in a much better position to reason about sizes.
On Wed, Feb 28, 2024 at 01:37:36PM -0800, Kees Cook wrote: > On Wed, Feb 28, 2024 at 10:41:32PM +0200, Andy Shevchenko wrote: ... > > +#define struct_data_pointer(p, a) PTR_ALIGN((void *)((p) + 1), (a)) > > I'm not super excited about propagating the "p + 1" code pattern to find > things after an allocation. This leads to the compiler either being > blind to accesses beyond an allocation, or being too conservative about > accesses beyond an object. Instead of these helpers I would much prefer > that data structures that use this code pattern be converted to using > trailing flexible arrays, at which point the compiler is in a much > better position to reason about sizes. There is nothing about flexible arrays in this. Maybe you have been confused by my choice for name of the macros. In that case I also can argue that current struct_size() is a good one. (something like struct_size_with_flex_array() can be more specific)
diff --git a/include/linux/overflow.h b/include/linux/overflow.h index bc390f026128..b93bbf1b6aaa 100644 --- a/include/linux/overflow.h +++ b/include/linux/overflow.h @@ -2,9 +2,10 @@ #ifndef __LINUX_OVERFLOW_H #define __LINUX_OVERFLOW_H +#include <linux/align.h> #include <linux/compiler.h> -#include <linux/limits.h> #include <linux/const.h> +#include <linux/limits.h> /* * We need to compute the minimum and maximum values representable in a given @@ -337,6 +338,30 @@ static inline size_t __must_check size_sub(size_t minuend, size_t subtrahend) */ #define array3_size(a, b, c) size_mul(size_mul(a, b), c) +/** + * struct_size_with_data() - Calculate size of structure with trailing aligned data. + * @p: Pointer to the structure. + * @a: Alignment in bytes before trailing data. + * @s: Data size in bytes (must not be 0). + * + * Calculates size of memory needed for structure of @p followed by an + * aligned data of size @s. + * + * Return: number of bytes needed or SIZE_MAX on overflow. + */ +#define struct_size_with_data(p, a, s) size_add(ALIGN(sizeof(*(p)), (a)), (s)) + +/** + * struct_data_pointer - Calculate offset of the trailing data reserved with + * struct_size_with_data(). + * @p: Pointer to the structure. + * @a: Alignment in bytes before trailing data. + * + * Return: offset in bytes to the trailing data reserved with + * struct_size_with_data(). + */ +#define struct_data_pointer(p, a) PTR_ALIGN((void *)((p) + 1), (a)) + /** * flex_array_size() - Calculate size of a flexible array member * within an enclosing structure.
Introduce two helper macros to calculate the size of the structure with trailing aligned data and to retrieve the pointer to that data. Signed-off-by: Andy Shevchenko <andriy.shevchenko@linux.intel.com> --- include/linux/overflow.h | 27 ++++++++++++++++++++++++++- 1 file changed, 26 insertions(+), 1 deletion(-)