Andi Kleen wrote:
Every byte in the [p,p+n[ range must be used. If you only use the
first byte, via e.g. asm("" :: "m"(*(char*)p)), then the compiler
_will_ skip scrubbing bytes beyond the first. This works with
gcc-3.2.3 up to gcc-4.4.3.
You forgot to credit Mikael who did all the hard work figuring
this out?
/*
+ * Dead store elimination (DSE) is an optimization that may remove a write to
+ * a buffer that is not used anymore. Use ARRAY_PREVENT_DSE after a write when
+ * the scrub is required for security reasons.
+ */
+#define ARRAY_PREVENT_DSE(p, n) \
Maybe it's just me, but the name is ugly.
+ do { \
+ struct __scrub { char c[n]; }; \
Better typeof(*p)[n]
+++ b/include/linux/compiler-intel.h
@@ -14,9 +14,11 @@
* It uses intrinsics to do the equivalent things.
*/
#undef barrier
+#undef ARRAY_PREVENT_DSE
#undef RELOC_HIDE
#define barrier() __memory_barrier()
+#define ARRAY_PREVENT_DSE(p, n)
Who says the Intel compiler doesn't need this?
I'm sure it does dead store elimination too and it understands
gcc asm syntax.
According to the Intel forum, it not only doesn't, but a request for this as a
feature was rejected, so it won't. Or am I misreading this?
http://software.intel.com/en-us/forums/showthread.php?t=46770
--
Bill Davidsen <davidsen@xxxxxxx>
"We have more to fear from the bungling of the incompetent than from
the machinations of the wicked." - from Slashdot
--
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
