The patch titled
Subject: kernel.h: skip single-eval logic on literals in min()/max()
has been added to the -mm tree. Its filename is
kernelh-skip-single-eval-logic-on-literals-in-min-max.patch
This patch should soon appear at
http://ozlabs.org/~akpm/mmots/broken-out/kernelh-skip-single-eval-logic-on-literals-in-min-max.patch
and later at
http://ozlabs.org/~akpm/mmotm/broken-out/kernelh-skip-single-eval-logic-on-literals-in-min-max.patch
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------------------------------------------------------
From: Kees Cook <keescook@xxxxxxxxxxxx>
Subject: kernel.h: skip single-eval logic on literals in min()/max()
When max() is used in stack array size calculations from literal values
(e.g. "char foo[max(sizeof(struct1), sizeof(struct2))]", the compiler
thinks this is a dynamic calculation due to the single-eval logic, which
is not needed in the literal case. This change removes several accidental
stack VLAs from an x86 allmodconfig build:
$ diff -u before.txt after.txt | grep ^-
-drivers/input/touchscreen/cyttsp4_core.c:871:2: warning: ISO C90 forbids variable length array `ids' [-Wvla]
-fs/btrfs/tree-checker.c:344:4: warning: ISO C90 forbids variable length array `namebuf' [-Wvla]
-lib/vsprintf.c:747:2: warning: ISO C90 forbids variable length array `sym' [-Wvla]
-net/ipv4/proc.c:403:2: warning: ISO C90 forbids variable length array `buff' [-Wvla]
-net/ipv6/proc.c:198:2: warning: ISO C90 forbids variable length array `buff' [-Wvla]
-net/ipv6/proc.c:218:2: warning: ISO C90 forbids variable length array `buff64' [-Wvla]
Based on an earlier patch from Josh Poimboeuf.
Link: http://lkml.kernel.org/r/20180308214045.GA6787@beast
Signed-off-by: Kees Cook <keescook@xxxxxxxxxxxx>
Reviewed-by: Andrew Morton <akpm@xxxxxxxxxxxxxxxxxxxx>
Cc: Josh Poimboeuf <jpoimboe@xxxxxxxxxx>
Cc: Rasmus Villemoes <linux@xxxxxxxxxxxxxxxxxx>
Cc: "Gustavo A. R. Silva" <gustavo@xxxxxxxxxxxxxx>
Cc: "Tobin C. Harding" <me@xxxxxxxx>
Cc: Steven Rostedt <rostedt@xxxxxxxxxxx>
Cc: Jonathan Corbet <corbet@xxxxxxx>
Cc: Chris Mason <clm@xxxxxx>
Cc: Josef Bacik <jbacik@xxxxxx>
Cc: David Sterba <dsterba@xxxxxxxx>
Cc: "David S. Miller" <davem@xxxxxxxxxxxxx>
Cc: Alexey Kuznetsov <kuznet@xxxxxxxxxxxxx>
Cc: Hideaki YOSHIFUJI <yoshfuji@xxxxxxxxxxxxxx>
Cc: Ingo Molnar <mingo@xxxxxxxxxx>
Cc: Peter Zijlstra <peterz@xxxxxxxxxxxxx>
Cc: Thomas Gleixner <tglx@xxxxxxxxxxxxx>
Cc: Masahiro Yamada <yamada.masahiro@xxxxxxxxxxxxx>
Cc: Borislav Petkov <bp@xxxxxxx>
Cc: Randy Dunlap <rdunlap@xxxxxxxxxxxxx>
Cc: Ian Abbott <abbotti@xxxxxxxxx>
Cc: Sergey Senozhatsky <sergey.senozhatsky.work@xxxxxxxxx>
Cc: Petr Mladek <pmladek@xxxxxxxx>
Cc: Andy Shevchenko <andriy.shevchenko@xxxxxxxxxxxxxxx>
Cc: Pantelis Antoniou <pantelis.antoniou@xxxxxxxxxxxx
Signed-off-by: Andrew Morton <akpm@xxxxxxxxxxxxxxxxxxxx>
---
diff -puN include/linux/kernel.h~kernelh-skip-single-eval-logic-on-literals-in-min-max include/linux/kernel.h
--- a/include/linux/kernel.h~kernelh-skip-single-eval-logic-on-literals-in-min-max
+++ a/include/linux/kernel.h
@@ -790,37 +790,57 @@ static inline void ftrace_dump(enum ftra
* strict type-checking.. See the
* "unnecessary" pointer comparison.
*/
-#define __min(t1, t2, min1, min2, x, y) ({ \
+#define __single_eval_min(t1, t2, min1, min2, x, y) ({ \
t1 min1 = (x); \
t2 min2 = (y); \
(void) (&min1 == &min2); \
min1 < min2 ? min1 : min2; })
+/*
+ * In the case of builtin constant values, there is no need to do the
+ * double-evaluation protection, so the raw comparison can be made.
+ * This allows min()/max() to be used in stack array allocations and
+ * avoid the compiler thinking it is a dynamic value leading to an
+ * accidental VLA.
+ */
+#define __min(t1, t2, x, y) \
+ __builtin_choose_expr(__builtin_constant_p(x) && \
+ __builtin_constant_p(y) && \
+ __builtin_types_compatible_p(t1, t2), \
+ (t1)(x) < (t2)(y) ? (t1)(x) : (t2)(y), \
+ __single_eval_min(t1, t2, \
+ __UNIQUE_ID(max1_), \
+ __UNIQUE_ID(max2_), \
+ x, y))
+
/**
* min - return minimum of two values of the same or compatible types
* @x: first value
* @y: second value
*/
-#define min(x, y) \
- __min(typeof(x), typeof(y), \
- __UNIQUE_ID(min1_), __UNIQUE_ID(min2_), \
- x, y)
+#define min(x, y) __min(typeof(x), typeof(y), x, y)
-#define __max(t1, t2, max1, max2, x, y) ({ \
+#define __single_eval_max(t1, t2, max1, max2, x, y) ({ \
t1 max1 = (x); \
t2 max2 = (y); \
(void) (&max1 == &max2); \
max1 > max2 ? max1 : max2; })
+#define __max(t1, t2, x, y) \
+ __builtin_choose_expr(__builtin_constant_p(x) && \
+ __builtin_constant_p(y) && \
+ __builtin_types_compatible_p(t1, t2), \
+ (t1)(x) > (t2)(y) ? (t1)(x) : (t2)(y), \
+ __single_eval_max(t1, t2, \
+ __UNIQUE_ID(max1_), \
+ __UNIQUE_ID(max2_), \
+ x, y))
/**
* max - return maximum of two values of the same or compatible types
* @x: first value
* @y: second value
*/
-#define max(x, y) \
- __max(typeof(x), typeof(y), \
- __UNIQUE_ID(max1_), __UNIQUE_ID(max2_), \
- x, y)
+#define max(x, y) __max(typeof(x), typeof(y), x, y)
/**
* min3 - return minimum of three values
@@ -874,7 +894,6 @@ static inline void ftrace_dump(enum ftra
*/
#define min_t(type, x, y) \
__min(type, type, \
- __UNIQUE_ID(min1_), __UNIQUE_ID(min2_), \
x, y)
/**
@@ -885,7 +904,6 @@ static inline void ftrace_dump(enum ftra
*/
#define max_t(type, x, y) \
__max(type, type, \
- __UNIQUE_ID(min1_), __UNIQUE_ID(min2_), \
x, y)
/**
_
Patches currently in -mm which might be from keescook@xxxxxxxxxxxx are
bug-use-%pb-in-bug-and-stack-protector-failure.patch
bug-exclude-non-bug-warn-exceptions-from-report_bug.patch
taint-convert-to-indexed-initialization.patch
taint-consolidate-documentation.patch
taint-add-taint-for-randstruct.patch
kernelh-skip-single-eval-logic-on-literals-in-min-max.patch
test_bitmap-do-not-accidentally-use-stack-vla.patch
fork-unconditionally-clear-stack-on-fork.patch
exec-pass-stack-rlimit-into-mm-layout-functions.patch
exec-introduce-finalize_exec-before-start_thread.patch
exec-pin-stack-limit-during-exec.patch
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