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MORE SHADOW WALKER: THE
PROGRESSION OF TLB-SPLITTING
ON X86
Jacob Torrey: Cyber SMEagol
@JacobTorrey
About Me
• Senior research engineer at Assured
Information Security ()
• Leads low-level computer architectures group
– SMM
– VMM
– BIOS
– Kernel
• Lover of the great outdoors
Outline
• Background
• History
– PaX/GRSecurity - Defensive
– Shadow Walker - Offensive
– MoRE - Defensive
– MoRE Shadow Walker - Offensive
• Conclusions
• Wrap up
Background
Virtual Memory
• Intel x86 provides OS method to abstract view
of memory: virtual memory / paging
Background
Page Translation
• Every memory access requires several memory bus
transactions to perform page translation
– This is slow!
Background
Translation Lookaside Buffer
• The solution to this problem is to cache previous translations
in a buffer called the Translation Lookaside Buffer (TLB)
Background
TLB Splitting
• The CPU’s TLB is used to cache memory page translations to
increase performance.
• De-synchronizing a CPU’s Translation Look-aside Buffer (TLB)
(e.g. Shadow Walker or PaX).
Background
Intel TLB
• In pre-Nehelam CPUs, the D-TLB and I-TLB
were completely separate:
Splitting the TLB
• On a pre-Nehelam CPU, the TLB is split by:
– Trapping on a fault (page or protection)
– Determining if data or instruction (check EIP and
CR2 or exit condition)
– “Priming” the proper TLB by either setting data
access bit(s) and
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