What Every Hacker Should Know About TLB Invalidation [pdf]

Within QEMU amd64&#x2F;x86 emulation (not KVM) mode, the IMUL opcode still fails its IMUL opcode emulation after an XOR opcode (also within the same TLB cached page) modified its neighbor IMUL operand(s).<p>TLB got double-invalidated yet some say never invalidated. The crux is a glitch within a singlr entire TLB invalidation operation thereby negating XOR opcode&#x27;s ability to self-modify the neighboring IMUL operand. (Double ROT13, anyone?). I assert double-invalidation because within the same TLB invalidation stroke, XOR operation got performed ... twice, as opposed to retrieving and restoring original IMUL operand value after such invalidation thereby negating XOR computed result EITHER WAY.<p>A failure of self-modifying code within QEMU amd64&#x2F;x86 emulation mode could be a useful test to determine if one is under QEMU emulation mode, of course if the page allows read-write-execute as often found in JavaScript, Java, Python and Dalvik (Android) bytecode memory regions.<p>Fabrice Bellard, author of QEMU, acknowledged the basic of above but failed amd64&#x2F;x86 IMUL&#x2F;XOR self-modify premise in emulation (not KVM) mode of QEMU.<p><a href="https:&#x2F;&#x2F;github.com&#x2F;unicorn-engine&#x2F;unicorn&#x2F;issues&#x2F;364">https:&#x2F;&#x2F;github.com&#x2F;unicorn-engine&#x2F;unicorn&#x2F;issues&#x2F;364</a>

Elaborate memory management (paging) systems need caching of lookups for high performance. But they can go wrong. The post was made in a security&#x2F;safety context but did I miss something, because it didn&#x27;t seems to make clear what the dangers are?

I&#x27;d be interested to see this written for reading (as opposed to presenting). Inferring the speaker&#x27;s meaning from raw slides is a little challenging. I&#x27;ve had to interact with the minutiae of the x86 TLB in a past life, but happily have forgotten most of that.