From: David Laight <David.Laight@xxxxxxxxxx> commit d03eba99f5bf7cbc6e2fdde3b6fa36954ad58e09 upstream. The type-check in min()/max() is there to stop unexpected results if a negative value gets converted to a large unsigned value. However it also rejects 'unsigned int' v 'unsigned long' compares which are common and never problematc. Replace the 'same type' check with a 'same signedness' check. The new test isn't itself a compile time error, so use static_assert() to report the error and give a meaningful error message. Due to the way builtin_choose_expr() works detecting the error in the 'non-constant' side (where static_assert() can be used) also detects errors when the arguments are constant. Link: https://lkml.kernel.org/r/fe7e6c542e094bfca655abcd323c1c98@xxxxxxxxxxxxxxxx Signed-off-by: David Laight <david.laight@xxxxxxxxxx> Cc: Andy Shevchenko <andriy.shevchenko@xxxxxxxxxxxxxxx> Cc: Christoph Hellwig <hch@xxxxxxxxxxxxx> Cc: Jason A. Donenfeld <Jason@xxxxxxxxx> Cc: Linus Torvalds <torvalds@xxxxxxxxxxxxxxxxxxxx> Cc: Matthew Wilcox (Oracle) <willy@xxxxxxxxxxxxx> Signed-off-by: Andrew Morton <akpm@xxxxxxxxxxxxxxxxxxxx> (cherry picked from commit d03eba99f5bf7cbc6e2fdde3b6fa36954ad58e09) Signed-off-by: SeongJae Park <sj@xxxxxxxxxx> Signed-off-by: Greg Kroah-Hartman <gregkh@xxxxxxxxxxxxxxxxxxx> --- include/linux/minmax.h | 62 ++++++++++++++++++++++++++----------------------- 1 file changed, 33 insertions(+), 29 deletions(-) --- a/include/linux/minmax.h +++ b/include/linux/minmax.h @@ -11,9 +11,8 @@ * * - avoid multiple evaluations of the arguments (so side-effects like * "x++" happen only once) when non-constant. - * - perform strict type-checking (to generate warnings instead of - * nasty runtime surprises). See the "unnecessary" pointer comparison - * in __typecheck(). + * - perform signed v unsigned type-checking (to generate compile + * errors instead of nasty runtime surprises). * - retain result as a constant expressions when called with only * constant expressions (to avoid tripping VLA warnings in stack * allocation usage). @@ -21,23 +20,30 @@ #define __typecheck(x, y) \ (!!(sizeof((typeof(x) *)1 == (typeof(y) *)1))) -#define __no_side_effects(x, y) \ - (__is_constexpr(x) && __is_constexpr(y)) +/* is_signed_type() isn't a constexpr for pointer types */ +#define __is_signed(x) \ + __builtin_choose_expr(__is_constexpr(is_signed_type(typeof(x))), \ + is_signed_type(typeof(x)), 0) -#define __safe_cmp(x, y) \ - (__typecheck(x, y) && __no_side_effects(x, y)) +#define __types_ok(x, y) \ + (__is_signed(x) == __is_signed(y)) -#define __cmp(x, y, op) ((x) op (y) ? (x) : (y)) +#define __cmp_op_min < +#define __cmp_op_max > -#define __cmp_once(x, y, unique_x, unique_y, op) ({ \ +#define __cmp(op, x, y) ((x) __cmp_op_##op (y) ? (x) : (y)) + +#define __cmp_once(op, x, y, unique_x, unique_y) ({ \ typeof(x) unique_x = (x); \ typeof(y) unique_y = (y); \ - __cmp(unique_x, unique_y, op); }) - -#define __careful_cmp(x, y, op) \ - __builtin_choose_expr(__safe_cmp(x, y), \ - __cmp(x, y, op), \ - __cmp_once(x, y, __UNIQUE_ID(__x), __UNIQUE_ID(__y), op)) + static_assert(__types_ok(x, y), \ + #op "(" #x ", " #y ") signedness error, fix types or consider u" #op "() before " #op "_t()"); \ + __cmp(op, unique_x, unique_y); }) + +#define __careful_cmp(op, x, y) \ + __builtin_choose_expr(__is_constexpr((x) - (y)), \ + __cmp(op, x, y), \ + __cmp_once(op, x, y, __UNIQUE_ID(__x), __UNIQUE_ID(__y))) #define __clamp(val, lo, hi) \ ((val) >= (hi) ? (hi) : ((val) <= (lo) ? (lo) : (val))) @@ -46,17 +52,15 @@ typeof(val) unique_val = (val); \ typeof(lo) unique_lo = (lo); \ typeof(hi) unique_hi = (hi); \ + static_assert(__builtin_choose_expr(__is_constexpr((lo) > (hi)), \ + (lo) <= (hi), true), \ + "clamp() low limit " #lo " greater than high limit " #hi); \ + static_assert(__types_ok(val, lo), "clamp() 'lo' signedness error"); \ + static_assert(__types_ok(val, hi), "clamp() 'hi' signedness error"); \ __clamp(unique_val, unique_lo, unique_hi); }) -#define __clamp_input_check(lo, hi) \ - (BUILD_BUG_ON_ZERO(__builtin_choose_expr( \ - __is_constexpr((lo) > (hi)), (lo) > (hi), false))) - #define __careful_clamp(val, lo, hi) ({ \ - __clamp_input_check(lo, hi) + \ - __builtin_choose_expr(__typecheck(val, lo) && __typecheck(val, hi) && \ - __typecheck(hi, lo) && __is_constexpr(val) && \ - __is_constexpr(lo) && __is_constexpr(hi), \ + __builtin_choose_expr(__is_constexpr((val) - (lo) + (hi)), \ __clamp(val, lo, hi), \ __clamp_once(val, lo, hi, __UNIQUE_ID(__val), \ __UNIQUE_ID(__lo), __UNIQUE_ID(__hi))); }) @@ -66,14 +70,14 @@ * @x: first value * @y: second value */ -#define min(x, y) __careful_cmp(x, y, <) +#define min(x, y) __careful_cmp(min, x, y) /** * max - return maximum of two values of the same or compatible types * @x: first value * @y: second value */ -#define max(x, y) __careful_cmp(x, y, >) +#define max(x, y) __careful_cmp(max, x, y) /** * umin - return minimum of two non-negative values @@ -82,7 +86,7 @@ * @y: second value */ #define umin(x, y) \ - __careful_cmp((x) + 0u + 0ul + 0ull, (y) + 0u + 0ul + 0ull, <) + __careful_cmp(min, (x) + 0u + 0ul + 0ull, (y) + 0u + 0ul + 0ull) /** * umax - return maximum of two non-negative values @@ -90,7 +94,7 @@ * @y: second value */ #define umax(x, y) \ - __careful_cmp((x) + 0u + 0ul + 0ull, (y) + 0u + 0ul + 0ull, >) + __careful_cmp(max, (x) + 0u + 0ul + 0ull, (y) + 0u + 0ul + 0ull) /** * min3 - return minimum of three values @@ -142,7 +146,7 @@ * @x: first value * @y: second value */ -#define min_t(type, x, y) __careful_cmp((type)(x), (type)(y), <) +#define min_t(type, x, y) __careful_cmp(min, (type)(x), (type)(y)) /** * max_t - return maximum of two values, using the specified type @@ -150,7 +154,7 @@ * @x: first value * @y: second value */ -#define max_t(type, x, y) __careful_cmp((type)(x), (type)(y), >) +#define max_t(type, x, y) __careful_cmp(max, (type)(x), (type)(y)) /** * clamp_t - return a value clamped to a given range using a given type Patches currently in stable-queue which might be from sj@xxxxxxxxxx are queue-5.15/minmax-allow-min-max-clamp-if-the-arguments-have-the-same-signedness.patch queue-5.15/minmax-sanity-check-constant-bounds-when-clamping.patch queue-5.15/minmax-clamp-more-efficiently-by-avoiding-extra-comparison.patch queue-5.15/minmax-relax-check-to-allow-comparison-between-unsigned-arguments-and-signed-constants.patch queue-5.15/minmax-fix-header-inclusions.patch queue-5.15/mm-damon-core-merge-regions-aggressively-when-max_nr_regions-is-unmet.patch queue-5.15/tracing-define-the-is_signed_type-macro-once.patch queue-5.15/minmax-allow-comparisons-of-int-against-unsigned-char-short.patch
