This is a note to let you know that I've just added the patch titled
minmax: sanity check constant bounds when clamping
to the 5.10-stable tree which can be found at:
http://www.kernel.org/git/?p=linux/kernel/git/stable/stable-queue.git;a=summary
The filename of the patch is:
minmax-sanity-check-constant-bounds-when-clamping.patch
and it can be found in the queue-5.10 subdirectory.
If you, or anyone else, feels it should not be added to the stable tree,
please let <[email protected]> know about it.
>From [email protected] Fri Oct 17
>11:08:22 2025
From: Eliav Farber <[email protected]>
Date: Fri, 17 Oct 2025 09:04:55 +0000
Subject: minmax: sanity check constant bounds when clamping
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Message-ID: <[email protected]>
From: "Jason A. Donenfeld" <[email protected]>
[ Upstream commit 5efcecd9a3b18078d3398b359a84c83f549e22cf ]
The clamp family of functions only makes sense if hi>=lo. If hi and lo
are compile-time constants, then raise a build error. Doing so has
already caught buggy code. This also introduces the infrastructure to
improve the clamping function in subsequent commits.
[[email protected]: coding-style cleanups]
[[email protected]: s@&&\@&& \@]
Link: https://lkml.kernel.org/r/[email protected]
Signed-off-by: Jason A. Donenfeld <[email protected]>
Reviewed-by: Andy Shevchenko <[email protected]>
Cc: Kees Cook <[email protected]>
Signed-off-by: Andrew Morton <[email protected]>
Signed-off-by: Eliav Farber <[email protected]>
Signed-off-by: Greg Kroah-Hartman <[email protected]>
---
include/linux/minmax.h | 26 ++++++++++++++++++++++++--
1 file changed, 24 insertions(+), 2 deletions(-)
--- a/include/linux/minmax.h
+++ b/include/linux/minmax.h
@@ -37,6 +37,28 @@
__cmp(x, y, op), \
__cmp_once(x, y, __UNIQUE_ID(__x), __UNIQUE_ID(__y), op))
+#define __clamp(val, lo, hi) \
+ __cmp(__cmp(val, lo, >), hi, <)
+
+#define __clamp_once(val, lo, hi, unique_val, unique_lo, unique_hi) ({ \
+ typeof(val) unique_val = (val); \
+ typeof(lo) unique_lo = (lo); \
+ typeof(hi) unique_hi = (hi); \
+ __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), \
+ __clamp(val, lo, hi), \
+ __clamp_once(val, lo, hi, __UNIQUE_ID(__val), \
+ __UNIQUE_ID(__lo), __UNIQUE_ID(__hi))); })
+
/**
* min - return minimum of two values of the same or compatible types
* @x: first value
@@ -103,7 +125,7 @@
* This macro does strict typechecking of @lo/@hi to make sure they are of the
* same type as @val. See the unnecessary pointer comparisons.
*/
-#define clamp(val, lo, hi) min((typeof(val))max(val, lo), hi)
+#define clamp(val, lo, hi) __careful_clamp(val, lo, hi)
/*
* ..and if you can't take the strict
@@ -138,7 +160,7 @@
* This macro does no typechecking and uses temporary variables of type
* @type to make all the comparisons.
*/
-#define clamp_t(type, val, lo, hi) min_t(type, max_t(type, val, lo), hi)
+#define clamp_t(type, val, lo, hi) __careful_clamp((type)(val), (type)(lo),
(type)(hi))
/**
* clamp_val - return a value clamped to a given range using val's type
Patches currently in stable-queue which might be from [email protected] are
queue-5.10/minmax-allow-comparisons-of-int-against-unsigned-char-short.patch
queue-5.10/minmax-add-a-few-more-min_t-max_t-users.patch
queue-5.10/minmax-improve-macro-expansion-and-type-checking.patch
queue-5.10/minmax-fix-indentation-of-__cmp_once-and-__clamp_once.patch
queue-5.10/minmax.h-simplify-the-variants-of-clamp.patch
queue-5.10/minmax-add-in_range-macro.patch
queue-5.10/minmax.h-move-all-the-clamp-definitions-after-the-min-max-ones.patch
queue-5.10/minmax-allow-min-max-clamp-if-the-arguments-have-the-same-signedness.patch
queue-5.10/minmax-don-t-use-max-in-situations-that-want-a-c-constant-expression.patch
queue-5.10/minmax.h-remove-some-defines-that-are-only-expanded-once.patch
queue-5.10/minmax.h-use-build_bug_on_msg-for-the-lo-hi-test-in-clamp.patch
queue-5.10/minmax-simplify-min-max-clamp-implementation.patch
queue-5.10/minmax-deduplicate-__unconst_integer_typeof.patch
queue-5.10/minmax-simplify-and-clarify-min_t-max_t-implementation.patch
queue-5.10/minmax.h-add-whitespace-around-operators-and-after-commas.patch
queue-5.10/minmax-sanity-check-constant-bounds-when-clamping.patch
queue-5.10/minmax-avoid-overly-complicated-constant-expressions-in-vm-code.patch
queue-5.10/minmax-make-generic-min-and-max-macros-available-everywhere.patch
queue-5.10/minmax-fix-up-min3-and-max3-too.patch
queue-5.10/minmax.h-reduce-the-define-expansion-of-min-max-and-clamp.patch
queue-5.10/minmax-fix-header-inclusions.patch
queue-5.10/minmax-introduce-min-max-_array.patch
queue-5.10/btrfs-remove-duplicated-in_range-macro.patch
queue-5.10/overflow-tracing-define-the-is_signed_type-macro-once.patch
queue-5.10/minmax-relax-check-to-allow-comparison-between-unsigned-arguments-and-signed-constants.patch
queue-5.10/minmax-clamp-more-efficiently-by-avoiding-extra-comparison.patch
queue-5.10/minmax.h-update-some-comments.patch
