This patch adds the Documentation/intel_mpx.txt file with some information about Intel MPX. Signed-off-by: Qiaowei Ren <qiaowei.ren@xxxxxxxxx> Signed-off-by: Xudong Hao <xudong.hao@xxxxxxxxx> Signed-off-by: Liu Jinsong <jinsong.liu@xxxxxxxxx> --- Documentation/x86/intel_mpx.txt | 76 +++++++++++++++++++++++++++++++++++++++ 1 files changed, 76 insertions(+), 0 deletions(-) create mode 100644 Documentation/x86/intel_mpx.txt diff --git a/Documentation/x86/intel_mpx.txt b/Documentation/x86/intel_mpx.txt new file mode 100644 index 0000000..778d06e --- /dev/null +++ b/Documentation/x86/intel_mpx.txt @@ -0,0 +1,76 @@ +Intel(R) MPX Overview: +===================== + +Intel(R) Memory Protection Extensions (Intel(R) MPX) is a new +capability introduced into Intel Architecture. Intel MPX can +increase the robustness of software when it is used in conjunction +with compiler changes to check that memory references intended +at compile time do not become unsafe at runtime. + +Two of the most important goals of Intel MPX are to provide +this capability at very low performance overhead for newly +compiled code, and to provide compatibility mechanisms with +legacy software components. A direct benefit Intel MPX provides +is hardening software against malicious attacks designed to +cause or exploit buffer overruns. + +For details about the Intel MPX instructions, see "Intel(R) +Architecture Instruction Set Extensions Programming Reference". + +Intel(R) MPX Programming Model +------------------------------ + +Intel MPX introduces new registers and new instructions that +operate on these registers. Some of the registers added are +bounds registers which store a pointer's lower bound and upper +bound limits. Whenever the pointer is used, the requested +reference is checked against the pointer's associated bounds, +thereby preventing out-of-bound memory access (such as buffer +overflows and overruns). Out-of-bounds memory references +initiate a #BR exception which can then be handled in an +appropriate manner. + +Loading and Storing Bounds using Translation +-------------------------------------------- + +Intel MPX defines two instructions for load/store of the linear +address of a pointer to a buffer, along with the bounds of the +buffer into a paging structure of extended bounds. Specifically +when storing extended bounds, the processor will perform address +translation of the address where the pointer is stored to an +address in the Bound Table (BT) to determine the store location +of extended bounds. Loading of an extended bounds performs the +reverse sequence. + +The structure in memory to load/store an extended bound is a +4-tuple consisting of lower bound, upper bound, pointer value +and a reserved field. Bound loads and stores access 32-bit or +64-bit operand size according to the operation mode. Thus, +a bound table entry is 4*32 bits in 32-bit mode and 4*64 bits +in 64-bit mode. + +The linear address of a bound table is stored in a Bound +Directory (BD) entry. And the linear address of the bound +directory is derived from either BNDCFGU or BNDCFGS registers. +Bounds in memory are stored in Bound Tables (BT) as an extended +bound, which are accessed via Bound Directory (BD) and address +translation performed by BNDLDX/BNDSTX instructions. + +Bounds Directory (BD) and Bounds Tables (BT) are stored in +application memory and are allocated by the application (in case +of kernel use, the structures will be in kernel memory). The +bound directory and each instance of bound table are in contiguous +linear memory. + +XSAVE/XRESTOR Support of Intel MPX State +---------------------------------------- + +Enabling Intel MPX requires an OS to manage two bits in XCR0: + - BNDREGS for saving and restoring registers BND0-BND3, + - BNDCSR for saving and restoring the user-mode configuration +(BNDCFGU) and the status register (BNDSTATUS). + +The reason for having two separate bits is that BND0-BND3 is +likely to be volatile state, while BNDCFGU and BNDSTATUS are not. +Therefore, an OS has flexibility in handling these two states +differently in saving or restoring them. -- 1.7.1 -- To unsubscribe from this list: send the line "unsubscribe kvm" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
