compiler.h: drop fallback overflow checkers
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
Linus Torvalds
parent
76ae847497
commit
4eb6bd55cf
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@ -62,19 +62,6 @@
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#define __no_sanitize_coverage
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#endif
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/*
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* Not all versions of clang implement the type-generic versions
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* of the builtin overflow checkers. Fortunately, clang implements
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* __has_builtin allowing us to avoid awkward version
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* checks. Unfortunately, we don't know which version of gcc clang
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* pretends to be, so the macro may or may not be defined.
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*/
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#if __has_builtin(__builtin_mul_overflow) && \
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__has_builtin(__builtin_add_overflow) && \
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__has_builtin(__builtin_sub_overflow)
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#define COMPILER_HAS_GENERIC_BUILTIN_OVERFLOW 1
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#endif
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#if __has_feature(shadow_call_stack)
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# define __noscs __attribute__((__no_sanitize__("shadow-call-stack")))
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#endif
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@ -128,10 +128,6 @@
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#define __no_sanitize_coverage
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#endif
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#if GCC_VERSION >= 50100
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#define COMPILER_HAS_GENERIC_BUILTIN_OVERFLOW 1
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#endif
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/*
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* Turn individual warnings and errors on and off locally, depending
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* on version.
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@ -6,12 +6,9 @@
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#include <linux/limits.h>
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/*
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* In the fallback code below, we need to compute the minimum and
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* maximum values representable in a given type. These macros may also
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* be useful elsewhere, so we provide them outside the
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* COMPILER_HAS_GENERIC_BUILTIN_OVERFLOW block.
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*
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* It would seem more obvious to do something like
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* We need to compute the minimum and maximum values representable in a given
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* type. These macros may also be useful elsewhere. It would seem more obvious
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* to do something like:
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*
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* #define type_min(T) (T)(is_signed_type(T) ? (T)1 << (8*sizeof(T)-1) : 0)
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* #define type_max(T) (T)(is_signed_type(T) ? ((T)1 << (8*sizeof(T)-1)) - 1 : ~(T)0)
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@ -54,7 +51,6 @@ static inline bool __must_check __must_check_overflow(bool overflow)
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return unlikely(overflow);
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}
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#ifdef COMPILER_HAS_GENERIC_BUILTIN_OVERFLOW
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/*
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* For simplicity and code hygiene, the fallback code below insists on
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* a, b and *d having the same type (similar to the min() and max()
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@ -90,134 +86,6 @@ static inline bool __must_check __must_check_overflow(bool overflow)
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__builtin_mul_overflow(__a, __b, __d); \
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}))
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#else
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/* Checking for unsigned overflow is relatively easy without causing UB. */
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#define __unsigned_add_overflow(a, b, d) ({ \
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typeof(a) __a = (a); \
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typeof(b) __b = (b); \
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typeof(d) __d = (d); \
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(void) (&__a == &__b); \
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(void) (&__a == __d); \
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*__d = __a + __b; \
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*__d < __a; \
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})
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#define __unsigned_sub_overflow(a, b, d) ({ \
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typeof(a) __a = (a); \
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typeof(b) __b = (b); \
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typeof(d) __d = (d); \
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(void) (&__a == &__b); \
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(void) (&__a == __d); \
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*__d = __a - __b; \
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__a < __b; \
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})
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/*
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* If one of a or b is a compile-time constant, this avoids a division.
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*/
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#define __unsigned_mul_overflow(a, b, d) ({ \
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typeof(a) __a = (a); \
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typeof(b) __b = (b); \
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typeof(d) __d = (d); \
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(void) (&__a == &__b); \
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(void) (&__a == __d); \
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*__d = __a * __b; \
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__builtin_constant_p(__b) ? \
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__b > 0 && __a > type_max(typeof(__a)) / __b : \
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__a > 0 && __b > type_max(typeof(__b)) / __a; \
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})
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/*
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* For signed types, detecting overflow is much harder, especially if
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* we want to avoid UB. But the interface of these macros is such that
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* we must provide a result in *d, and in fact we must produce the
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* result promised by gcc's builtins, which is simply the possibly
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* wrapped-around value. Fortunately, we can just formally do the
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* operations in the widest relevant unsigned type (u64) and then
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* truncate the result - gcc is smart enough to generate the same code
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* with and without the (u64) casts.
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*/
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/*
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* Adding two signed integers can overflow only if they have the same
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* sign, and overflow has happened iff the result has the opposite
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* sign.
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*/
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#define __signed_add_overflow(a, b, d) ({ \
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typeof(a) __a = (a); \
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typeof(b) __b = (b); \
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typeof(d) __d = (d); \
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(void) (&__a == &__b); \
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(void) (&__a == __d); \
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*__d = (u64)__a + (u64)__b; \
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(((~(__a ^ __b)) & (*__d ^ __a)) \
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& type_min(typeof(__a))) != 0; \
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})
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/*
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* Subtraction is similar, except that overflow can now happen only
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* when the signs are opposite. In this case, overflow has happened if
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* the result has the opposite sign of a.
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*/
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#define __signed_sub_overflow(a, b, d) ({ \
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typeof(a) __a = (a); \
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typeof(b) __b = (b); \
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typeof(d) __d = (d); \
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(void) (&__a == &__b); \
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(void) (&__a == __d); \
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*__d = (u64)__a - (u64)__b; \
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((((__a ^ __b)) & (*__d ^ __a)) \
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& type_min(typeof(__a))) != 0; \
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})
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/*
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* Signed multiplication is rather hard. gcc always follows C99, so
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* division is truncated towards 0. This means that we can write the
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* overflow check like this:
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*
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* (a > 0 && (b > MAX/a || b < MIN/a)) ||
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* (a < -1 && (b > MIN/a || b < MAX/a) ||
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* (a == -1 && b == MIN)
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*
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* The redundant casts of -1 are to silence an annoying -Wtype-limits
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* (included in -Wextra) warning: When the type is u8 or u16, the
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* __b_c_e in check_mul_overflow obviously selects
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* __unsigned_mul_overflow, but unfortunately gcc still parses this
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* code and warns about the limited range of __b.
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*/
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#define __signed_mul_overflow(a, b, d) ({ \
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typeof(a) __a = (a); \
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typeof(b) __b = (b); \
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typeof(d) __d = (d); \
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typeof(a) __tmax = type_max(typeof(a)); \
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typeof(a) __tmin = type_min(typeof(a)); \
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(void) (&__a == &__b); \
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(void) (&__a == __d); \
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*__d = (u64)__a * (u64)__b; \
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(__b > 0 && (__a > __tmax/__b || __a < __tmin/__b)) || \
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(__b < (typeof(__b))-1 && (__a > __tmin/__b || __a < __tmax/__b)) || \
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(__b == (typeof(__b))-1 && __a == __tmin); \
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})
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#define check_add_overflow(a, b, d) __must_check_overflow( \
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__builtin_choose_expr(is_signed_type(typeof(a)), \
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__signed_add_overflow(a, b, d), \
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__unsigned_add_overflow(a, b, d)))
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#define check_sub_overflow(a, b, d) __must_check_overflow( \
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__builtin_choose_expr(is_signed_type(typeof(a)), \
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__signed_sub_overflow(a, b, d), \
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__unsigned_sub_overflow(a, b, d)))
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#define check_mul_overflow(a, b, d) __must_check_overflow( \
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__builtin_choose_expr(is_signed_type(typeof(a)), \
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__signed_mul_overflow(a, b, d), \
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__unsigned_mul_overflow(a, b, d)))
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#endif /* COMPILER_HAS_GENERIC_BUILTIN_OVERFLOW */
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/** check_shl_overflow() - Calculate a left-shifted value and check overflow
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*
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* @a: Value to be shifted
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@ -38,7 +38,3 @@
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#endif
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#define __printf(a, b) __attribute__((format(printf, a, b)))
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#define __scanf(a, b) __attribute__((format(scanf, a, b)))
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#if GCC_VERSION >= 50100
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#define COMPILER_HAS_GENERIC_BUILTIN_OVERFLOW 1
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#endif
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@ -5,12 +5,9 @@
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#include <linux/compiler.h>
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/*
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* In the fallback code below, we need to compute the minimum and
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* maximum values representable in a given type. These macros may also
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* be useful elsewhere, so we provide them outside the
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* COMPILER_HAS_GENERIC_BUILTIN_OVERFLOW block.
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*
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* It would seem more obvious to do something like
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* We need to compute the minimum and maximum values representable in a given
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* type. These macros may also be useful elsewhere. It would seem more obvious
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* to do something like:
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*
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* #define type_min(T) (T)(is_signed_type(T) ? (T)1 << (8*sizeof(T)-1) : 0)
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* #define type_max(T) (T)(is_signed_type(T) ? ((T)1 << (8*sizeof(T)-1)) - 1 : ~(T)0)
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@ -36,8 +33,6 @@
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#define type_max(T) ((T)((__type_half_max(T) - 1) + __type_half_max(T)))
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#define type_min(T) ((T)((T)-type_max(T)-(T)1))
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#ifdef COMPILER_HAS_GENERIC_BUILTIN_OVERFLOW
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/*
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* For simplicity and code hygiene, the fallback code below insists on
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* a, b and *d having the same type (similar to the min() and max()
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@ -73,135 +68,6 @@
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__builtin_mul_overflow(__a, __b, __d); \
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})
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#else
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/* Checking for unsigned overflow is relatively easy without causing UB. */
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#define __unsigned_add_overflow(a, b, d) ({ \
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typeof(a) __a = (a); \
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typeof(b) __b = (b); \
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typeof(d) __d = (d); \
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(void) (&__a == &__b); \
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(void) (&__a == __d); \
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*__d = __a + __b; \
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*__d < __a; \
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})
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#define __unsigned_sub_overflow(a, b, d) ({ \
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typeof(a) __a = (a); \
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typeof(b) __b = (b); \
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typeof(d) __d = (d); \
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(void) (&__a == &__b); \
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(void) (&__a == __d); \
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*__d = __a - __b; \
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__a < __b; \
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})
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/*
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* If one of a or b is a compile-time constant, this avoids a division.
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*/
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#define __unsigned_mul_overflow(a, b, d) ({ \
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typeof(a) __a = (a); \
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typeof(b) __b = (b); \
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typeof(d) __d = (d); \
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(void) (&__a == &__b); \
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(void) (&__a == __d); \
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*__d = __a * __b; \
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__builtin_constant_p(__b) ? \
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__b > 0 && __a > type_max(typeof(__a)) / __b : \
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__a > 0 && __b > type_max(typeof(__b)) / __a; \
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})
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/*
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* For signed types, detecting overflow is much harder, especially if
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* we want to avoid UB. But the interface of these macros is such that
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* we must provide a result in *d, and in fact we must produce the
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* result promised by gcc's builtins, which is simply the possibly
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* wrapped-around value. Fortunately, we can just formally do the
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* operations in the widest relevant unsigned type (u64) and then
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* truncate the result - gcc is smart enough to generate the same code
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* with and without the (u64) casts.
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*/
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/*
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* Adding two signed integers can overflow only if they have the same
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* sign, and overflow has happened iff the result has the opposite
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* sign.
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*/
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#define __signed_add_overflow(a, b, d) ({ \
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typeof(a) __a = (a); \
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typeof(b) __b = (b); \
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typeof(d) __d = (d); \
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(void) (&__a == &__b); \
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(void) (&__a == __d); \
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*__d = (u64)__a + (u64)__b; \
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(((~(__a ^ __b)) & (*__d ^ __a)) \
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& type_min(typeof(__a))) != 0; \
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})
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/*
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* Subtraction is similar, except that overflow can now happen only
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* when the signs are opposite. In this case, overflow has happened if
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* the result has the opposite sign of a.
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*/
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#define __signed_sub_overflow(a, b, d) ({ \
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typeof(a) __a = (a); \
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typeof(b) __b = (b); \
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typeof(d) __d = (d); \
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(void) (&__a == &__b); \
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(void) (&__a == __d); \
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*__d = (u64)__a - (u64)__b; \
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((((__a ^ __b)) & (*__d ^ __a)) \
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& type_min(typeof(__a))) != 0; \
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})
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/*
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* Signed multiplication is rather hard. gcc always follows C99, so
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* division is truncated towards 0. This means that we can write the
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* overflow check like this:
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*
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* (a > 0 && (b > MAX/a || b < MIN/a)) ||
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* (a < -1 && (b > MIN/a || b < MAX/a) ||
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* (a == -1 && b == MIN)
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*
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* The redundant casts of -1 are to silence an annoying -Wtype-limits
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* (included in -Wextra) warning: When the type is u8 or u16, the
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* __b_c_e in check_mul_overflow obviously selects
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* __unsigned_mul_overflow, but unfortunately gcc still parses this
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* code and warns about the limited range of __b.
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*/
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#define __signed_mul_overflow(a, b, d) ({ \
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typeof(a) __a = (a); \
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typeof(b) __b = (b); \
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typeof(d) __d = (d); \
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typeof(a) __tmax = type_max(typeof(a)); \
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typeof(a) __tmin = type_min(typeof(a)); \
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(void) (&__a == &__b); \
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(void) (&__a == __d); \
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*__d = (u64)__a * (u64)__b; \
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(__b > 0 && (__a > __tmax/__b || __a < __tmin/__b)) || \
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(__b < (typeof(__b))-1 && (__a > __tmin/__b || __a < __tmax/__b)) || \
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(__b == (typeof(__b))-1 && __a == __tmin); \
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})
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#define check_add_overflow(a, b, d) \
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__builtin_choose_expr(is_signed_type(typeof(a)), \
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__signed_add_overflow(a, b, d), \
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__unsigned_add_overflow(a, b, d))
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#define check_sub_overflow(a, b, d) \
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__builtin_choose_expr(is_signed_type(typeof(a)), \
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__signed_sub_overflow(a, b, d), \
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__unsigned_sub_overflow(a, b, d))
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#define check_mul_overflow(a, b, d) \
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__builtin_choose_expr(is_signed_type(typeof(a)), \
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__signed_mul_overflow(a, b, d), \
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__unsigned_mul_overflow(a, b, d))
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#endif /* COMPILER_HAS_GENERIC_BUILTIN_OVERFLOW */
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/**
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* array_size() - Calculate size of 2-dimensional array.
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*
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