4.15-stable review patch.  If anyone has any objections, please let me know.


From: Rasmus Villemoes <li...@rasmusvillemoes.dk>

commit b98c6a160a057d5686a8c54c79cc6c8c94a7d0c8 upstream.

The last expression in a statement expression need not be a bare
variable, quoting gcc docs

  The last thing in the compound statement should be an expression
  followed by a semicolon; the value of this subexpression serves as the
  value of the entire construct.

and we already use that in e.g. the min/max macros which end with a
ternary expression.

This way, we can allow index to have const-qualified type, which will in
some cases avoid the need for introducing a local copy of index of
non-const qualified type. That, in turn, can prevent readers not
familiar with the internals of array_index_nospec from wondering about
the seemingly redundant extra variable, and I think that's worthwhile
considering how confusing the whole _nospec business is.

The expression _i&_mask has type unsigned long (since that is the type
of _mask, and the BUILD_BUG_ONs guarantee that _i will get promoted to
that), so in order not to change the type of the whole expression, add
a cast back to typeof(_i).

Signed-off-by: Rasmus Villemoes <li...@rasmusvillemoes.dk>
Signed-off-by: Dan Williams <dan.j.willi...@intel.com>
Acked-by: Linus Torvalds <torva...@linux-foundation.org>
Cc: Andy Lutomirski <l...@kernel.org>
Cc: Arjan van de Ven <ar...@linux.intel.com>
Cc: Borislav Petkov <b...@alien8.de>
Cc: Dave Hansen <dave.han...@linux.intel.com>
Cc: David Woodhouse <dw...@infradead.org>
Cc: Greg Kroah-Hartman <gre...@linuxfoundation.org>
Cc: Josh Poimboeuf <jpoim...@redhat.com>
Cc: Peter Zijlstra <pet...@infradead.org>
Cc: Thomas Gleixner <t...@linutronix.de>
Cc: Will Deacon <will.dea...@arm.com>
Cc: linux-a...@vger.kernel.org
Cc: sta...@vger.kernel.org
Signed-off-by: Ingo Molnar <mi...@kernel.org>
Signed-off-by: Greg Kroah-Hartman <gre...@linuxfoundation.org>

 include/linux/nospec.h |    3 +--
 1 file changed, 1 insertion(+), 2 deletions(-)

--- a/include/linux/nospec.h
+++ b/include/linux/nospec.h
@@ -72,7 +72,6 @@ static inline unsigned long array_index_
        BUILD_BUG_ON(sizeof(_i) > sizeof(long));                        \
        BUILD_BUG_ON(sizeof(_s) > sizeof(long));                        \
-       _i &= _mask;                                                    \
-       _i;                                                             \
+       (typeof(_i)) (_i & _mask);                                      \
 #endif /* _LINUX_NOSPEC_H */

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