Intel MPX

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Intel MPX (Memory Protection Extensions) is a set of extensions to the x86 instruction set architecture. With compiler, runtime library and operating system support, Intel MPX brings increased security to software by checking pointer references whose normal compile-time intentions are maliciously exploited at runtime due to buffer overflows. Intel MPX introduces new bounds registers, and new instruction set extensions that operate on these registers. Additionally, there is a new set of "bound tables" that store bounds beyond what can fit in the bounds registers.[1][2][3][4][5]

MPX uses four new 128-bit bounds registers, BND0 to BND3, each storing a pair of 64-bit lower bound (LB) and upper bound (UB) values of a buffer. The upper bound is stored in ones' complement form, with BNDMK (create bounds) and BNDCU (check upper bound) performing the conversion. The architecture includes two configuration registers BNDCFGx (BNDCFGU in user space and BNDCFGS in kernel mode), and a status register BNDSTATUS, which provides a memory address and error code in case of an exception.[6][7]

Two-level address translation is used for storing bounds in memory. The top layer consists of a Bounds Directory (BD) created on the application startup. Each BD entry is either empty or contains a pointer to a dynamically created Bounds Table (BT), which in turn contains a set of pointer bounds along with the linear addresses of the pointers. The bounds load (BNDLDX) and store (BNDSTX) instructions transparently perform the address translation and access bounds in the proper BT entry.[6][7]

Intel MPX was introduced as part of the Skylake microarchitecture.[8] Kernel-level software support for Intel MPX was merged into the Linux kernel mainline in kernel version 3.19, which was released on February 8, 2015.[9][10]

Intel Goldmont microarchitecture also supports Intel MPX.[11]


  1. ^ "Intel ISA Extensions". Intel. Retrieved 2013-11-04. 
  2. ^ "Introduction to Intel Memory Protection Extensions". Intel. 2013-07-16. Retrieved 2013-09-10. 
  3. ^ "Discussion of Intel Memory Protection Extensions (MPX) and comparison with AddressSanitizer". Retrieved 2013-11-04. 
  4. ^ "Intel Memory Protection Extensions (Intel MPX) support in the GCC compiler". Retrieved 2013-11-04. 
  5. ^ "Intel MPX Explained: Storing bounds in memory". Retrieved 2017-02-06. 
  6. ^ a b "Intel Architecture Instruction Set Extensions Programming Reference" (PDF). Intel. December 2013. Retrieved 2014-01-17. 
  7. ^ a b Oleksenko, Oleksii; Kuvaiskii, Dmitrii; Bhatotia, Pramod; Felber, Pascal; Fetzer, Christof (2017). "Intel MPX Explained: An Empirical Study of Intel MPX and Software-based Bounds Checking Approaches". arXiv:1702.00719Freely accessible [cs.CR]. 
  8. ^ "Intel Software Development Emulator". Intel. 2012-06-15. Retrieved 2013-11-04. 
  9. ^ "Linux kernel 3.19, Section 1.2. Support for the Intel Memory Protection Extensions". February 9, 2015. Retrieved February 9, 2015. 
  10. ^ Jonathan Corbet (January 29, 2014). "Supporting Intel MPX in Linux". Retrieved February 9, 2015. 
  11. ^ "Intel Software Development Emulator". 

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