The patch titled
Subject: minmax: sanity check constant bounds when clamping
has been added to the -mm mm-nonmm-unstable branch. Its filename is
minmax-sanity-check-constant-bounds-when-clamping.patch
This patch will shortly appear at
https://git.kernel.org/pub/scm/linux/kernel/git/akpm/25-new.git/tree/patches/minmax-sanity-check-constant-bounds-when-clamping.patch
This patch will later appear in the mm-nonmm-unstable branch at
git://git.kernel.org/pub/scm/linux/kernel/git/akpm/mm
Before you just go and hit "reply", please:
a) Consider who else should be cc'ed
b) Prefer to cc a suitable mailing list as well
c) Ideally: find the original patch on the mailing list and do a
reply-to-all to that, adding suitable additional cc's
*** Remember to use Documentation/process/submit-checklist.rst when testing your code ***
The -mm tree is included into linux-next via the mm-everything
branch at git://git.kernel.org/pub/scm/linux/kernel/git/akpm/mm
and is updated there every 2-3 working days
------------------------------------------------------
From: "Jason A. Donenfeld" <Jason@xxxxxxxxx>
Subject: minmax: sanity check constant bounds when clamping
Date: Mon, 26 Sep 2022 15:34:34 +0200
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.
Link: https://lkml.kernel.org/r/20220926133435.1333846-1-Jason@xxxxxxxxx
Signed-off-by: Jason A. Donenfeld <Jason@xxxxxxxxx>
Reviewed-by: Andy Shevchenko <andriy.shevchenko@xxxxxxxxxxxxxxx>
Cc: Kees Cook <keescook@xxxxxxxxxxxx>
Signed-off-by: Andrew Morton <akpm@xxxxxxxxxxxxxxxxxxxx>
---
include/linux/minmax.h | 26 ++++++++++++++++++++++++--
1 file changed, 24 insertions(+), 2 deletions(-)
--- a/include/linux/minmax.h~minmax-sanity-check-constant-bounds-when-clamping
+++ a/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
@@ -86,7 +108,7 @@
* 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
@@ -121,7 +143,7 @@
* 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 -mm which might be from Jason@xxxxxxxxx are
minmax-sanity-check-constant-bounds-when-clamping.patch
minmax-clamp-more-efficiently-by-avoiding-extra-comparison.patch
