bianbu-repo-mirror/bianbu-linux-6.6
1
0
Fork 0
mirror of https://gitee.com/bianbu-linux/linux-6.6 synced 2025-07-01 23:53:16 -04:00
Code Issues Projects Releases Packages Wiki Activity Actions

overflow: Introduce overflows_type() and castable_to_type()

Browse source 
Implement a robust overflows_type() macro to test if a variable or
constant value would overflow another variable or type. This can be
used as a constant expression for static_assert() (which requires a
constant expression[1][2]) when used on constant values. This must be
constructed manually, since __builtin_add_overflow() does not produce
a constant expression[3].

Additionally adds castable_to_type(), similar to __same_type(), but for
checking if a constant value would overflow if cast to a given type.

Add unit tests for overflows_type(), __same_type(), and castable_to_type()
to the existing KUnit "overflow" test:

[16:03:33] ================== overflow (21 subtests) ==================
...
[16:03:33] [PASSED] overflows_type_test
[16:03:33] [PASSED] same_type_test
[16:03:33] [PASSED] castable_to_type_test
[16:03:33] ==================== [PASSED] overflow =====================
[16:03:33] ============================================================
[16:03:33] Testing complete. Ran 21 tests: passed: 21
[16:03:33] Elapsed time: 24.022s total, 0.002s configuring, 22.598s building, 0.767s running

[1] https://en.cppreference.com/w/c/language/_Static_assert
[2] C11 standard (ISO/IEC 9899:2011): 6.7.10 Static assertions
[3] https://gcc.gnu.org/onlinedocs/gcc/Integer-Overflow-Builtins.html
    6.56 Built-in Functions to Perform Arithmetic with Overflow Checking
    Built-in Function: bool __builtin_add_overflow (type1 a, type2 b,

Cc: Luc Van Oostenryck <luc.vanoostenryck@gmail.com>
Cc: Nathan Chancellor <nathan@kernel.org>
Cc: Nick Desaulniers <ndesaulniers@google.com>
Cc: Tom Rix <trix@redhat.com>
Cc: Daniel Latypov <dlatypov@google.com>
Cc: Vitor Massaru Iha <vitor@massaru.org>
Cc: "Gustavo A. R. Silva" <gustavoars@kernel.org>
Cc: Jani Nikula <jani.nikula@intel.com>
Cc: Mauro Carvalho Chehab <mchehab@kernel.org>
Cc: linux-hardening@vger.kernel.org
Cc: llvm@lists.linux.dev
Co-developed-by: Gwan-gyeong Mun <gwan-gyeong.mun@intel.com>
Signed-off-by: Gwan-gyeong Mun <gwan-gyeong.mun@intel.com>
Signed-off-by: Kees Cook <keescook@chromium.org>
Link: https://lore.kernel.org/r/20221024201125.1416422-1-gwan-gyeong.mun@intel.com
This commit is contained in:
Kees Cook 2022-10-24 23:11:25 +03:00
parent 6dd142d901
commit 4b21d25bf5
6 changed files with 431 additions and 5 deletions
Download patch file Download diff file Expand all files Collapse all files

47
include/linux/overflow.h
View file

@ -128,6 +128,53 @@ static inline bool __must_check __must_check_overflow(bool overflow)
(*_d >> _to_shift) != _a); \
}))
#define __overflows_type_constexpr(x, T) ( \
is_unsigned_type(typeof(x)) ? \
(x) > type_max(typeof(T)) : \
is_unsigned_type(typeof(T)) ? \
(x) < 0 || (x) > type_max(typeof(T)) : \
(x) < type_min(typeof(T)) || (x) > type_max(typeof(T)))
#define __overflows_type(x, T) ({ \
typeof(T) v = 0; \
check_add_overflow((x), v, &v); \
})
/**
* overflows_type - helper for checking the overflows between value, variables,
* or data type
*
* @n: source constant value or variable to be checked
* @T: destination variable or data type proposed to store @x
*
* Compares the @x expression for whether or not it can safely fit in
* the storage of the type in @T. @x and @T can have different types.
* If @x is a constant expression, this will also resolve to a constant
* expression.
*
* Returns: true if overflow can occur, false otherwise.
*/
#define overflows_type(n, T) \
__builtin_choose_expr(__is_constexpr(n), \
__overflows_type_constexpr(n, T), \
__overflows_type(n, T))
/**
* castable_to_type - like __same_type(), but also allows for casted literals
*
* @n: variable or constant value
* @T: variable or data type
*
* Unlike the __same_type() macro, this allows a constant value as the
* first argument. If this value would not overflow into an assignment
* of the second argument's type, it returns true. Otherwise, this falls
* back to __same_type().
*/
#define castable_to_type(n, T) \
__builtin_choose_expr(__is_constexpr(n), \
!__overflows_type_constexpr(n, T), \
__same_type(n, T))
/**
* size_mul() - Calculate size_t multiplication with saturation at SIZE_MAX
* @factor1: first factor