On Wed, Apr 29, 2015 at 04:01:19PM +0200, Daniel Borkmann wrote: > On 04/29/2015 03:08 PM, mancha security wrote: > ... > >By the way, has anyone been able to verify that __memory_barrier > >provides DSE protection under various optimizations? Unfortunately, I > >don't have ready access to ICC at the moment or I'd test it myself. > > Never used icc, but it looks like it's free for open source projects; > I can give it a try, but in case you're faster than I am, feel free > to post results here. Time permitting, I'll try setting this up and post my results. > > From what I see based on the code, i.e. after that buggy cleanup > commit ... > > commit 73679e50820123ebdedc67ebcda4562d1d6e4aba > Author: Pranith Kumar <bobby.prani@xxxxxxxxx> > Date: Tue Apr 15 12:05:22 2014 -0400 > > compiler-intel.h: Remove duplicate definition > > barrier is already defined as __memory_barrier in compiler.h > Remove this unnecessary redefinition. > > Signed-off-by: Pranith Kumar <bobby.prani@xxxxxxxxx> > Link: http://lkml.kernel.org/r/CAJhHMCAnYPy0%2BqD-1KBnJPLt3XgAjdR12j%2BySSnPgmZcpbE7HQ@xxxxxxxxxxxxxx > Signed-off-by: H. Peter Anvin <hpa@xxxxxxxxxxxxxxx> > > ... it looks like it's currently using the _same_ gcc inline asm > for the barrier on icc instead of what that commit intended to do. > > So funny enough, we don't actually use __memory_barrier() at the > moment. ;) > > Nonetheless, having a look might be good. Nice catch, 73679e50820 is indeed buggy because ICC defines __GNUC__ (unless -no-gcc is used). That should be reverted. Bug aside, according to [1], ICC does support GNU-style inline asm so for the purposes of barrier_data(), it would be interesting to see if it affords better/worse DSE protection compared to __memory_barrier(). --mancha [1] https://software.intel.com/sites/products/documentation/doclib/iss/2013/compiler/cpp-lin/GUID-5100C4FC-BC2F-4E36-943A-120CFFFB4285.htm
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