On Wed, May 4, 2016 at 5:52 PM, John Denker <jsd@xxxxxxxx> wrote: > On 05/04/2016 02:42 PM, I wrote: > >> I find it very odd that the other seven functions were not >> upgraded. I suggest the attached fix-others.diff would make >> things more consistent. > > Here's a replacement patch. > ... +1, commit it. Its good for three additional reasons. First, this change means the kernel is teaching the next generation the correct way to do things. Many developers aspire to be kernel hackers, and they sometimes use the code from bitops.h. I've actually run across the code in production during an audit where the developers cited bitops.h. Second, it preserves a "silent and dark" cockpit during analysis. That is, when analysis is run, no findings are generated. Auditors and security folks like quiet tools, much like the way pilots like their cockpits (flashing lights and sounding buzzers usually means something is wrong). Third, the pattern is recognized by the major compilers, so the kernel should not have any trouble when porting any of the compilers. I often use multiple compiler to tease out implementation defined behavior in a effort to achieve greater portability. Here are the citations to ensure the kernel is safe with the pattern: * GCC: http://gcc.gnu.org/bugzilla/show_bug.cgi?id=57157 * ICC: http://software.intel.com/en-us/forums/topic/580884 However, Clang may cause trouble because they don't want the responsibility of recognizing the pattern: * https://llvm.org/bugs/show_bug.cgi?id=24226#c8 Instead, they provide a defective rotate. The "defect" here is its non-constant time due to the branch, so it may not be suitable for high-integrity or high-assurance code like linux-crypto: * https://llvm.org/bugs/show_bug.cgi?id=24226#c5 Jeff -- To unsubscribe from this list: send the line "unsubscribe linux-crypto" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
