[Intel-gfx] [PATCH v8 1/8] overflow: Move and add few utility macros into overflow

[Andrzej Hajda]

On 23.08.2022 12:17, Gwan-gyeong Mun wrote:
> It moves overflows_type utility macro into overflow header from i915_utils
> header. The overflows_type can be used to catch the truncaion (overflow)
> between different data types. And it adds check_assign() macro which
> performs an assigning source value into destination ptr along with an
> overflow check. overflow_type macro has been improved to handle the signbit
> by gcc's built-in overflow check function. And it adds overflows_ptr()
> helper macro for checking the overflows between a value and a pointer
> type/value.
> 
> v3: Add is_type_unsigned() macro (Mauro)
>      Modify overflows_type() macro to consider signed data types (Mauro)
>      Fix the problem that safe_conversion() macro always returns true
> v4: Fix kernel-doc markups
> v6: Move macro addition location so that it can be used by other than drm
>      subsystem (Jani, Mauro, Andi)
>      Change is_type_unsigned to is_unsigned_type to have the same name form
>      as is_signed_type macro
> v8: Add check_assign() and remove safe_conversion() (Kees)
>      Fix overflows_type() to use gcc's built-in overflow function (Andrzej)
>      Add overflows_ptr() to allow overflow checking when assigning a value
>      into a pointer variable (G.G.)
> 
> Signed-off-by: Gwan-gyeong Mun <gwan-gyeong.mun at intel.com>
> Cc: Thomas Hellström <thomas.hellstrom at linux.intel.com>
> Cc: Matthew Auld <matthew.auld at intel.com>
> Cc: Nirmoy Das <nirmoy.das at intel.com>
> Cc: Jani Nikula <jani.nikula at intel.com>
> Cc: Andi Shyti <andi.shyti at linux.intel.com>
> Cc: Andrzej Hajda <andrzej.hajda at intel.com>
> Cc: Mauro Carvalho Chehab <mauro.chehab at linux.intel.com>
> Cc: Kees Cook <keescook at chromium.org>
> Reviewed-by: Mauro Carvalho Chehab <mchehab at kernel.org> (v5)
> ---
>   drivers/gpu/drm/i915/i915_user_extensions.c |  2 +-
>   drivers/gpu/drm/i915/i915_utils.h           |  5 +-
>   include/linux/overflow.h                    | 67 +++++++++++++++++++++
>   3 files changed, 69 insertions(+), 5 deletions(-)
> 
> diff --git a/drivers/gpu/drm/i915/i915_user_extensions.c b/drivers/gpu/drm/i915/i915_user_extensions.c
> index c822d0aafd2d..0fb2fecbcaae 100644
> --- a/drivers/gpu/drm/i915/i915_user_extensions.c
> +++ b/drivers/gpu/drm/i915/i915_user_extensions.c
> @@ -51,7 +51,7 @@ int i915_user_extensions(struct i915_user_extension __user *ext,
>   			return err;
>   
>   		if (get_user(next, &ext->next_extension) ||
> -		    overflows_type(next, ext))
> +		    overflows_ptr(next, ext))
>   			return -EFAULT;
>   
>   		ext = u64_to_user_ptr(next);
> diff --git a/drivers/gpu/drm/i915/i915_utils.h b/drivers/gpu/drm/i915/i915_utils.h
> index c10d68cdc3ca..eb0ded23fa9c 100644
> --- a/drivers/gpu/drm/i915/i915_utils.h
> +++ b/drivers/gpu/drm/i915/i915_utils.h
> @@ -32,6 +32,7 @@
>   #include <linux/types.h>
>   #include <linux/workqueue.h>
>   #include <linux/sched/clock.h>
> +#include <linux/overflow.h>
>   
>   #ifdef CONFIG_X86
>   #include <asm/hypervisor.h>
> @@ -111,10 +112,6 @@ bool i915_error_injected(void);
>   #define range_overflows_end_t(type, start, size, max) \
>   	range_overflows_end((type)(start), (type)(size), (type)(max))
>   
> -/* Note we don't consider signbits :| */
> -#define overflows_type(x, T) \
> -	(sizeof(x) > sizeof(T) && (x) >> BITS_PER_TYPE(T))
> -
>   #define ptr_mask_bits(ptr, n) ({					\
>   	unsigned long __v = (unsigned long)(ptr);			\
>   	(typeof(ptr))(__v & -BIT(n));					\
> diff --git a/include/linux/overflow.h b/include/linux/overflow.h
> index f1221d11f8e5..4016f1378bcc 100644
> --- a/include/linux/overflow.h
> +++ b/include/linux/overflow.h
> @@ -52,6 +52,73 @@ static inline bool __must_check __must_check_overflow(bool overflow)
>   	return unlikely(overflow);
>   }
>   
> +/**
> + * overflows_type - helper for checking the overflows between data types or
> + *                  values
> + *
> + * @x: Source value or data type for overflow check
> + * @T: Destination value or data type for overflow check
> + *
> + * It compares the values or data type between the first and second argument to
> + * check whether overflow can occur when assigning the first argument to the
> + * variable of the second argument. Source and Destination can be singned or
> + * unsigned data types.
> + *
> + * Returns:
> + * True if overflow can occur, false otherwise.
> + */
> +#define overflows_type(x, T) __must_check_overflow(({	\
> +	typeof(T) v = 0;				\
> +	__builtin_add_overflow_p((x), v, v);		\


Above works since gcc7, since gcc5 you can use:
	__builtin_add_overflow((x), v, &v);


> +}))
> +
> +/**
> + * overflows_ptr - helper for checking the overflows between a value and
> + *                 a pointer type/value
> + *
> + * @x: Source value for overflow check
> + * @T: Destination pointer type or value for overflow check
> + *
> + * gcc's built-in overflow check functions don't support checking between the
> + * pointer type and non-pointer type. Therefore it compares the values and
> + * size of each data type between the first and second argument to check whether
> + * truncation can occur when assigning the first argument to the variable of the
> + * second argument. It checks internally the ptr is a pointer type.
> + *
> + * Returns:
> + * True if overflow can occur, false otherwise.
> + */
> +#define overflows_ptr(x, T) __must_check_overflow(({	\
> +	typecheck_pointer(T);				\
> +	((x) < 0) ? 1 : (sizeof(x) > sizeof(T) && (x) >> BITS_PER_TYPE(T)) ? 1 : 0; \
> +}))


Doesn't linux assume that all pointers have size of long int ?
Or at least all pointers have the same size.
In such case we can use:
#define overflows_ptr(x) overflows_type(x, unsigned long)

Regards
Andrzej

> +
> +/**
> + * check_assign - perform an assigning source value into destination ptr along
> + *                with an overflow check.
> + *
> + * @value: Source value
> + * @ptr: Destination pointer address, If the pointer type is not used,
> + *       a warning message is output during build.
> + *
> + * It checks internally the ptr is a pointer type. And it uses gcc's built-in
> + * overflow check function.
> + * It does not use the check_*() wrapper functions, but directly uses gcc's
> + * built-in overflow check function so that it can be used even when
> + * the type of value and the type pointed to by ptr are different without build
> + * warning messages.
> + *
> + * Returns:
> + * If the value would overflow the destination, it returns true. If not return
> + * false. When overflow does not occur, the assigning into ptr from value
> + * succeeds. It follows the return policy as other check_*_overflow() functions
> + * return non-zero as a failure.
> + */
> +#define check_assign(value, ptr) __must_check_overflow(({	\
> +	typecheck_pointer(ptr); 		\
> +	__builtin_add_overflow(0, value, ptr);	\
> +}))
> +
>   /*
>    * For simplicity and code hygiene, the fallback code below insists on
>    * a, b and *d having the same type (similar to the min() and max()