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   1 From sj@kernel.org Tue Jul 16 20:33:46 2024
   2 From: SeongJae Park <sj@kernel.org>
   3 Date: Tue, 16 Jul 2024 11:33:32 -0700
   4 Subject: minmax: relax check to allow comparison between unsigned arguments and signed constants
   5 To: stable@vger.kernel.org, gregkh@linuxfoundation.org
   6 Cc: David Laight <David.Laight@ACULAB.COM>, linux-kernel@vger.kernel.org, David Laight <david.laight@aculab.com>, Andy Shevchenko <andriy.shevchenko@linux.intel.com>, Christoph Hellwig <hch@infradead.org>, "Jason A . Donenfeld" <Jason@zx2c4.com>, Linus Torvalds <torvalds@linux-foundation.org>, Matthew Wilcox <willy@infradead.org>, Andrew Morton <akpm@linux-foundation.org>, SeongJae Park <sj@kernel.org>
   7 Message-ID: <20240716183333.138498-8-sj@kernel.org>
   8
   9 From: David Laight <David.Laight@ACULAB.COM>
  10
  11 commit 867046cc7027703f60a46339ffde91a1970f2901 upstream.
  12
  13 Allow (for example) min(unsigned_var, 20).
  14
  15 The opposite min(signed_var, 20u) is still errored.
  16
  17 Since a comparison between signed and unsigned never makes the unsigned
  18 value negative it is only necessary to adjust the __types_ok() test.
  19
  20 Link: https://lkml.kernel.org/r/633b64e2f39e46bb8234809c5595b8c7@AcuMS.aculab.com
  21 Signed-off-by: David Laight <david.laight@aculab.com>
  22 Cc: Andy Shevchenko <andriy.shevchenko@linux.intel.com>
  23 Cc: Christoph Hellwig <hch@infradead.org>
  24 Cc: Jason A. Donenfeld <Jason@zx2c4.com>
  25 Cc: Linus Torvalds <torvalds@linux-foundation.org>
  26 Cc: Matthew Wilcox (Oracle) <willy@infradead.org>
  27 Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
  28 (cherry picked from commit 867046cc7027703f60a46339ffde91a1970f2901)
  29 Signed-off-by: SeongJae Park <sj@kernel.org>
  30 Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
  31 ---
  32  include/linux/minmax.h |   24 +++++++++++++++++-------
  33  1 file changed, 17 insertions(+), 7 deletions(-)
  34
  35 --- a/include/linux/minmax.h
  36 +++ b/include/linux/minmax.h
  37 @@ -9,13 +9,18 @@
  38  /*
  39   * min()/max()/clamp() macros must accomplish three things:
  40   *
  41 - * - avoid multiple evaluations of the arguments (so side-effects like
  42 + * - Avoid multiple evaluations of the arguments (so side-effects like
  43   *   "x++" happen only once) when non-constant.
  44 - * - perform signed v unsigned type-checking (to generate compile
  45 - *   errors instead of nasty runtime surprises).
  46 - * - retain result as a constant expressions when called with only
  47 + * - Retain result as a constant expressions when called with only
  48   *   constant expressions (to avoid tripping VLA warnings in stack
  49   *   allocation usage).
  50 + * - Perform signed v unsigned type-checking (to generate compile
  51 + *   errors instead of nasty runtime surprises).
  52 + * - Unsigned char/short are always promoted to signed int and can be
  53 + *   compared against signed or unsigned arguments.
  54 + * - Unsigned arguments can be compared against non-negative signed constants.
  55 + * - Comparison of a signed argument against an unsigned constant fails
  56 + *   even if the constant is below __INT_MAX__ and could be cast to int.
  57   */
  58  #define __typecheck(x, y) \
  59         (!!(sizeof((typeof(x) *)1 == (typeof(y) *)1)))
  60 @@ -25,9 +30,14 @@
  61         __builtin_choose_expr(__is_constexpr(is_signed_type(typeof(x))),        \
  62                 is_signed_type(typeof(x)), 0)
  63
  64 -#define __types_ok(x, y)                       \
  65 -       (__is_signed(x) == __is_signed(y) ||    \
  66 -               __is_signed((x) + 0) == __is_signed((y) + 0))
  67 +/* True for a non-negative signed int constant */
  68 +#define __is_noneg_int(x)      \
  69 +       (__builtin_choose_expr(__is_constexpr(x) && __is_signed(x), x, -1) >= 0)
  70 +
  71 +#define __types_ok(x, y)                                       \
  72 +       (__is_signed(x) == __is_signed(y) ||                    \
  73 +               __is_signed((x) + 0) == __is_signed((y) + 0) || \
  74 +               __is_noneg_int(x) || __is_noneg_int(y))
  75
  76  #define __cmp_op_min <
  77  #define __cmp_op_max >