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A comment on Breaking the x86 Instruction Set: how to find undocumented x86 instructions. Parent comment

Re:Breaking the x86 Instruction Set: how to find undocumente... by vardump on Monday September 11, 2017 @05:37AM (#15217219)
You don't really need even that.

You just need a set of magic register values, like how CPUID [0] instruction already works.

[0]: http://www.sandpile.org/x86/cpuid.htm

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Re:Breaking the x86 Instruction Set: how to find undocumente... by jevinskie on Monday September 11, 2017 @12:02PM (#15219515)
Yup, this was done in this years USENIX with AMD microcode. See the exploits that check for magic register values at [0] and the paper at [1].

[0]: https://github.com/RUB-SysSec/Microcode/tree/master/updates

[1]: http://syssec.rub.de/research/publications/microcode-reversi...

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