This is a note to let you know that I've just added the patch titled
nospec: Allow index argument to have const-qualified type
to the 4.9-stable tree which can be found at: http://www.kernel.org/git/?p=linux/kernel/git/stable/stable-queue.git%3Ba=su...
The filename of the patch is: nospec-allow-index-argument-to-have-const-qualified-type.patch and it can be found in the queue-4.9 subdirectory.
If you, or anyone else, feels it should not be added to the stable tree, please let stable@vger.kernel.org know about it.
From b98c6a160a057d5686a8c54c79cc6c8c94a7d0c8 Mon Sep 17 00:00:00 2001
From: Rasmus Villemoes linux@rasmusvillemoes.dk Date: Fri, 16 Feb 2018 13:20:48 -0800 Subject: nospec: Allow index argument to have const-qualified type
From: Rasmus Villemoes linux@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 linux@rasmusvillemoes.dk Signed-off-by: Dan Williams dan.j.williams@intel.com Acked-by: Linus Torvalds torvalds@linux-foundation.org Cc: Andy Lutomirski luto@kernel.org Cc: Arjan van de Ven arjan@linux.intel.com Cc: Borislav Petkov bp@alien8.de Cc: Dave Hansen dave.hansen@linux.intel.com Cc: David Woodhouse dwmw2@infradead.org Cc: Greg Kroah-Hartman gregkh@linuxfoundation.org Cc: Josh Poimboeuf jpoimboe@redhat.com Cc: Peter Zijlstra peterz@infradead.org Cc: Thomas Gleixner tglx@linutronix.de Cc: Will Deacon will.deacon@arm.com Cc: linux-arch@vger.kernel.org Cc: stable@vger.kernel.org Link: http://lkml.kernel.org/r/151881604837.17395.10812767547837568328.stgit@dwill... Signed-off-by: Ingo Molnar mingo@kernel.org Signed-off-by: Greg Kroah-Hartman gregkh@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 */
Patches currently in stable-queue which might be from linux@rasmusvillemoes.dk are
queue-4.9/nospec-allow-index-argument-to-have-const-qualified-type.patch