[PATCH v7 1/8] overflow: Move and add few utility macros into overflow

Gwan-gyeong Mun
2022-08-16T11:11:59Z

It moves overflows_type utility macro into overflow header from i915_utils
header. The overflows_type can be used to catch the truncation between data
types. And it adds safe_conversion() macro which performs a type conversion
(cast) of an source value into a new variable, checking that the
destination is large enough to hold the source value. And the functionality
of overflows_type has been improved to handle the signbit.
The is_unsigned_type macro has been added to check the sign bit of the
built-in type.

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

Signed-off-by: Gwan-gyeong Mun <gwan-gyeong.mun@intel.com>
Cc: Thomas Hellström <thomas.hellstrom@linux.intel.com>
Cc: Matthew Auld <matthew.auld@intel.com>
Cc: Nirmoy Das <nirmoy.das@intel.com>
Cc: Jani Nikula <jani.nikula@intel.com>
Cc: Andi Shyti <andi.shyti@linux.intel.com>
Reviewed-by: Mauro Carvalho Chehab <mchehab@kernel.org> (v5)
---
drivers/gpu/drm/i915/i915_utils.h | 5 +--
include/linux/overflow.h | 54 +++++++++++++++++++++++++++++++
2 files changed, 55 insertions(+), 4 deletions(-)

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..462a03454377 100644
--- a/include/linux/overflow.h
+++ b/include/linux/overflow.h
@@ -35,6 +35,60 @@
#define type_max(T) ((T)((__type_half_max(T) - 1) + __type_half_max(T)))
#define type_min(T) ((T)((T)-type_max(T)-(T)1))

+/**
+ * is_unsigned_type - helper for checking data type which is an unsigned data
+ * type or not
+ * @x: The data type to check
+ *
+ * Returns:
+ * True if the data type is an unsigned data type, false otherwise.
+ */
+#define is_unsigned_type(x) ((typeof(x))-1 >= (typeof(x))0)
+
+/**
+ * overflows_type - helper for checking the truncation between data types
+ * @x: Source for overflow type comparison
+ * @T: Destination for overflow type comparison
+ *
+ * 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.
+ * Source and Destination can be used with or without sign bit.
+ * Composite data structures such as union and structure are not considered.
+ * Enum data types are not considered.
+ * Floating point data types are not considered.
+ *
+ * Returns:
+ * True if truncation can occur, false otherwise.
+ */
+#define overflows_type(x, T) \
+ (is_unsigned_type(x) ? \
+ is_unsigned_type(T) ? \
+ (sizeof(x) > sizeof(T) && (x) >> BITS_PER_TYPE(T)) ? 1 : 0 \
+ : (sizeof(x) >= sizeof(T) && (x) >> (BITS_PER_TYPE(T) - 1)) ? 1 : 0 \
+ : is_unsigned_type(T) ? \
+ ((x) < 0) ? 1 : (sizeof(x) > sizeof(T) && (x) >> BITS_PER_TYPE(T)) ? 1 : 0 \
+ : (sizeof(x) > sizeof(T)) ? \
+ ((x) < 0) ? (((x) * -1) >> BITS_PER_TYPE(T)) ? 1 : 0 \
+ : ((x) >> BITS_PER_TYPE(T)) ? 1 : 0 \
+ : 0)
+
+/**
+ * safe_conversion - perform a type conversion (cast) of an source value into
+ * a new variable, checking that the destination is large enough to hold the
+ * source value.
+ * @ptr: Destination pointer address
+ * @value: Source value
+ *
+ * Returns:
+ * If the value would overflow the destination, it returns false.
+ */
+#define safe_conversion(ptr, value) ({ \
+ typeof(value) __v = (value); \
+ typeof(ptr) __ptr = (ptr); \
+ overflows_type(__v, *__ptr) ? 0 : ((*__ptr = (typeof(*__ptr))__v), 1); \
+})
+
/*
* Avoids triggering -Wtype-limits compilation warning,
* while using unsigned data types to check a < 0.
--
2.37.1