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compiler.h: drop fallback overflow checkers

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Once upgrading the minimum supported version of GCC to 5.1, we can drop
the fallback code for !COMPILER_HAS_GENERIC_BUILTIN_OVERFLOW.

This is effectively a revert of commit f0907827a8 ("compiler.h: enable
builtin overflow checkers and add fallback code")

Link: https://github.com/ClangBuiltLinux/linux/issues/1438#issuecomment-916745801
Suggested-by: Rasmus Villemoes <linux@rasmusvillemoes.dk>
Signed-off-by: Nick Desaulniers <ndesaulniers@google.com>
Acked-by: Kees Cook <keescook@chromium.org>
Reviewed-by: Nathan Chancellor <nathan@kernel.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
This commit is contained in:
Nick Desaulniers 2021-09-10 16:40:39 -07:00 committed by Linus Torvalds
parent 76ae847497
commit 4eb6bd55cf
5 changed files with 6 additions and 293 deletions
Show Stats Download Patch File Download Diff File Expand all files Collapse all files

13
include/linux/compiler-clang.h
View File

@ -62,19 +62,6 @@
#define __no_sanitize_coverage
#endif
/*
* Not all versions of clang implement the type-generic versions
* of the builtin overflow checkers. Fortunately, clang implements
* __has_builtin allowing us to avoid awkward version
* checks. Unfortunately, we don't know which version of gcc clang
* pretends to be, so the macro may or may not be defined.
*/
#if __has_builtin(__builtin_mul_overflow) && \
__has_builtin(__builtin_add_overflow) && \
__has_builtin(__builtin_sub_overflow)
#define COMPILER_HAS_GENERIC_BUILTIN_OVERFLOW 1
#endif
#if __has_feature(shadow_call_stack)
# define __noscs __attribute__((__no_sanitize__("shadow-call-stack")))
#endif

4
include/linux/compiler-gcc.h
View File

@ -128,10 +128,6 @@
#define __no_sanitize_coverage
#endif
#if GCC_VERSION >= 50100
#define COMPILER_HAS_GENERIC_BUILTIN_OVERFLOW 1
#endif
/*
* Turn individual warnings and errors on and off locally, depending
* on version.

138
include/linux/overflow.h
View File

@ -6,12 +6,9 @@
#include <linux/limits.h>
/*
* In the fallback code below, we need to compute the minimum and
* maximum values representable in a given type. These macros may also
* be useful elsewhere, so we provide them outside the
* COMPILER_HAS_GENERIC_BUILTIN_OVERFLOW block.
*
* It would seem more obvious to do something like
* We need to compute the minimum and maximum values representable in a given
* type. These macros may also be useful elsewhere. It would seem more obvious
* to do something like:
*
* #define type_min(T) (T)(is_signed_type(T) ? (T)1 << (8*sizeof(T)-1) : 0)
* #define type_max(T) (T)(is_signed_type(T) ? ((T)1 << (8*sizeof(T)-1)) - 1 : ~(T)0)
@ -54,7 +51,6 @@ static inline bool __must_check __must_check_overflow(bool overflow)
return unlikely(overflow);
}
#ifdef COMPILER_HAS_GENERIC_BUILTIN_OVERFLOW
/*
* 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()
@ -90,134 +86,6 @@ static inline bool __must_check __must_check_overflow(bool overflow)
__builtin_mul_overflow(__a, __b, __d); \
}))
#else
/* Checking for unsigned overflow is relatively easy without causing UB. */
#define __unsigned_add_overflow(a, b, d) ({ \
typeof(a) __a = (a); \
typeof(b) __b = (b); \
typeof(d) __d = (d); \
(void) (&__a == &__b); \
(void) (&__a == __d); \
*__d = __a + __b; \
*__d < __a; \
})
#define __unsigned_sub_overflow(a, b, d) ({ \
typeof(a) __a = (a); \
typeof(b) __b = (b); \
typeof(d) __d = (d); \
(void) (&__a == &__b); \
(void) (&__a == __d); \
*__d = __a - __b; \
__a < __b; \
})
/*
* If one of a or b is a compile-time constant, this avoids a division.
*/
#define __unsigned_mul_overflow(a, b, d) ({ \
typeof(a) __a = (a); \
typeof(b) __b = (b); \
typeof(d) __d = (d); \
(void) (&__a == &__b); \
(void) (&__a == __d); \
*__d = __a * __b; \
__builtin_constant_p(__b) ? \
__b > 0 && __a > type_max(typeof(__a)) / __b : \
__a > 0 && __b > type_max(typeof(__b)) / __a; \
})
/*
* For signed types, detecting overflow is much harder, especially if
* we want to avoid UB. But the interface of these macros is such that
* we must provide a result in *d, and in fact we must produce the
* result promised by gcc's builtins, which is simply the possibly
* wrapped-around value. Fortunately, we can just formally do the
* operations in the widest relevant unsigned type (u64) and then
* truncate the result - gcc is smart enough to generate the same code
* with and without the (u64) casts.
*/
/*
* Adding two signed integers can overflow only if they have the same
* sign, and overflow has happened iff the result has the opposite
* sign.
*/
#define __signed_add_overflow(a, b, d) ({ \
typeof(a) __a = (a); \
typeof(b) __b = (b); \
typeof(d) __d = (d); \
(void) (&__a == &__b); \
(void) (&__a == __d); \
*__d = (u64)__a + (u64)__b; \
(((~(__a ^ __b)) & (*__d ^ __a)) \
& type_min(typeof(__a))) != 0; \
})
/*
* Subtraction is similar, except that overflow can now happen only
* when the signs are opposite. In this case, overflow has happened if
* the result has the opposite sign of a.
*/
#define __signed_sub_overflow(a, b, d) ({ \
typeof(a) __a = (a); \
typeof(b) __b = (b); \
typeof(d) __d = (d); \
(void) (&__a == &__b); \
(void) (&__a == __d); \
*__d = (u64)__a - (u64)__b; \
((((__a ^ __b)) & (*__d ^ __a)) \
& type_min(typeof(__a))) != 0; \
})
/*
* Signed multiplication is rather hard. gcc always follows C99, so
* division is truncated towards 0. This means that we can write the
* overflow check like this:
*
* (a > 0 && (b > MAX/a || b < MIN/a)) ||
* (a < -1 && (b > MIN/a || b < MAX/a) ||
* (a == -1 && b == MIN)
*
* The redundant casts of -1 are to silence an annoying -Wtype-limits
* (included in -Wextra) warning: When the type is u8 or u16, the
* __b_c_e in check_mul_overflow obviously selects
* __unsigned_mul_overflow, but unfortunately gcc still parses this
* code and warns about the limited range of __b.
*/
#define __signed_mul_overflow(a, b, d) ({ \
typeof(a) __a = (a); \
typeof(b) __b = (b); \
typeof(d) __d = (d); \
typeof(a) __tmax = type_max(typeof(a)); \
typeof(a) __tmin = type_min(typeof(a)); \
(void) (&__a == &__b); \
(void) (&__a == __d); \
*__d = (u64)__a * (u64)__b; \
(__b > 0 && (__a > __tmax/__b || __a < __tmin/__b)) || \
(__b < (typeof(__b))-1 && (__a > __tmin/__b || __a < __tmax/__b)) || \
(__b == (typeof(__b))-1 && __a == __tmin); \
})
#define check_add_overflow(a, b, d) __must_check_overflow( \
__builtin_choose_expr(is_signed_type(typeof(a)), \
__signed_add_overflow(a, b, d), \
__unsigned_add_overflow(a, b, d)))
#define check_sub_overflow(a, b, d) __must_check_overflow( \
__builtin_choose_expr(is_signed_type(typeof(a)), \
__signed_sub_overflow(a, b, d), \
__unsigned_sub_overflow(a, b, d)))
#define check_mul_overflow(a, b, d) __must_check_overflow( \
__builtin_choose_expr(is_signed_type(typeof(a)), \
__signed_mul_overflow(a, b, d), \
__unsigned_mul_overflow(a, b, d)))
#endif /* COMPILER_HAS_GENERIC_BUILTIN_OVERFLOW */
/** check_shl_overflow() - Calculate a left-shifted value and check overflow
*
* @a: Value to be shifted

4
tools/include/linux/compiler-gcc.h
View File

@ -38,7 +38,3 @@
#endif
#define __printf(a, b) __attribute__((format(printf, a, b)))
#define __scanf(a, b) __attribute__((format(scanf, a, b)))
#if GCC_VERSION >= 50100
#define COMPILER_HAS_GENERIC_BUILTIN_OVERFLOW 1
#endif

140
tools/include/linux/overflow.h
View File

@ -5,12 +5,9 @@
#include <linux/compiler.h>
/*
* In the fallback code below, we need to compute the minimum and
* maximum values representable in a given type. These macros may also
* be useful elsewhere, so we provide them outside the
* COMPILER_HAS_GENERIC_BUILTIN_OVERFLOW block.
*
* It would seem more obvious to do something like
* We need to compute the minimum and maximum values representable in a given
* type. These macros may also be useful elsewhere. It would seem more obvious
* to do something like:
*
* #define type_min(T) (T)(is_signed_type(T) ? (T)1 << (8*sizeof(T)-1) : 0)
* #define type_max(T) (T)(is_signed_type(T) ? ((T)1 << (8*sizeof(T)-1)) - 1 : ~(T)0)
@ -36,8 +33,6 @@
#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))
#ifdef COMPILER_HAS_GENERIC_BUILTIN_OVERFLOW
/*
* 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()
@ -73,135 +68,6 @@
__builtin_mul_overflow(__a, __b, __d); \
})
#else
/* Checking for unsigned overflow is relatively easy without causing UB. */
#define __unsigned_add_overflow(a, b, d) ({ \
typeof(a) __a = (a); \
typeof(b) __b = (b); \
typeof(d) __d = (d); \
(void) (&__a == &__b); \
(void) (&__a == __d); \
*__d = __a + __b; \
*__d < __a; \
})
#define __unsigned_sub_overflow(a, b, d) ({ \
typeof(a) __a = (a); \
typeof(b) __b = (b); \
typeof(d) __d = (d); \
(void) (&__a == &__b); \
(void) (&__a == __d); \
*__d = __a - __b; \
__a < __b; \
})
/*
* If one of a or b is a compile-time constant, this avoids a division.
*/
#define __unsigned_mul_overflow(a, b, d) ({ \
typeof(a) __a = (a); \
typeof(b) __b = (b); \
typeof(d) __d = (d); \
(void) (&__a == &__b); \
(void) (&__a == __d); \
*__d = __a * __b; \
__builtin_constant_p(__b) ? \
__b > 0 && __a > type_max(typeof(__a)) / __b : \
__a > 0 && __b > type_max(typeof(__b)) / __a; \
})
/*
* For signed types, detecting overflow is much harder, especially if
* we want to avoid UB. But the interface of these macros is such that
* we must provide a result in *d, and in fact we must produce the
* result promised by gcc's builtins, which is simply the possibly
* wrapped-around value. Fortunately, we can just formally do the
* operations in the widest relevant unsigned type (u64) and then
* truncate the result - gcc is smart enough to generate the same code
* with and without the (u64) casts.
*/
/*
* Adding two signed integers can overflow only if they have the same
* sign, and overflow has happened iff the result has the opposite
* sign.
*/
#define __signed_add_overflow(a, b, d) ({ \
typeof(a) __a = (a); \
typeof(b) __b = (b); \
typeof(d) __d = (d); \
(void) (&__a == &__b); \
(void) (&__a == __d); \
*__d = (u64)__a + (u64)__b; \
(((~(__a ^ __b)) & (*__d ^ __a)) \
& type_min(typeof(__a))) != 0; \
})
/*
* Subtraction is similar, except that overflow can now happen only
* when the signs are opposite. In this case, overflow has happened if
* the result has the opposite sign of a.
*/
#define __signed_sub_overflow(a, b, d) ({ \
typeof(a) __a = (a); \
typeof(b) __b = (b); \
typeof(d) __d = (d); \
(void) (&__a == &__b); \
(void) (&__a == __d); \
*__d = (u64)__a - (u64)__b; \
((((__a ^ __b)) & (*__d ^ __a)) \
& type_min(typeof(__a))) != 0; \
})
/*
* Signed multiplication is rather hard. gcc always follows C99, so
* division is truncated towards 0. This means that we can write the
* overflow check like this:
*
* (a > 0 && (b > MAX/a || b < MIN/a)) ||
* (a < -1 && (b > MIN/a || b < MAX/a) ||
* (a == -1 && b == MIN)
*
* The redundant casts of -1 are to silence an annoying -Wtype-limits
* (included in -Wextra) warning: When the type is u8 or u16, the
* __b_c_e in check_mul_overflow obviously selects
* __unsigned_mul_overflow, but unfortunately gcc still parses this
* code and warns about the limited range of __b.
*/
#define __signed_mul_overflow(a, b, d) ({ \
typeof(a) __a = (a); \
typeof(b) __b = (b); \
typeof(d) __d = (d); \
typeof(a) __tmax = type_max(typeof(a)); \
typeof(a) __tmin = type_min(typeof(a)); \
(void) (&__a == &__b); \
(void) (&__a == __d); \
*__d = (u64)__a * (u64)__b; \
(__b > 0 && (__a > __tmax/__b || __a < __tmin/__b)) || \
(__b < (typeof(__b))-1 && (__a > __tmin/__b || __a < __tmax/__b)) || \
(__b == (typeof(__b))-1 && __a == __tmin); \
})
#define check_add_overflow(a, b, d) \
__builtin_choose_expr(is_signed_type(typeof(a)), \
__signed_add_overflow(a, b, d), \
__unsigned_add_overflow(a, b, d))
#define check_sub_overflow(a, b, d) \
__builtin_choose_expr(is_signed_type(typeof(a)), \
__signed_sub_overflow(a, b, d), \
__unsigned_sub_overflow(a, b, d))
#define check_mul_overflow(a, b, d) \
__builtin_choose_expr(is_signed_type(typeof(a)), \
__signed_mul_overflow(a, b, d), \
__unsigned_mul_overflow(a, b, d))
#endif /* COMPILER_HAS_GENERIC_BUILTIN_OVERFLOW */
/**
* array_size() - Calculate size of 2-dimensional array.
*