| 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@dwillia2-desk3.amr.corp.intel.com |
| 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 */ |