--- b/Documentation/x86/protection-keys.txt | 65 ++++++++++++++++++++++++++++++++ 1 file changed, 65 insertions(+) diff -puN /dev/null Documentation/x86/protection-keys.txt --- /dev/null 2015-07-13 14:24:11.435656502 -0700 +++ b/Documentation/x86/protection-keys.txt 2015-09-16 09:45:55.874491904 -0700 @@ -0,0 +1,65 @@ +Memory Protection Keys for Userspace (PKU aka PKEYs) is a CPU feature +which will be found on future Intel CPUs. + +Memory Protection Keys provides a mechanism for enforcing page-based +protections, but without requiring modification of the page tables +when an application changes protection domains. It works by +dedicating 4 previously ignored bits in each page table entry to a +"protection key", giving 16 possible keys. + +There is also a new user-accessible register (PKRU) with two separate +bits (Access Disable and Write Disable) for each key. Being a CPU +register, PKRU is inherently thread-local, potentially giving each +thread a different set of protections from every other thread. + +There are two new instructions (RDPKRU/WRPKRU) for reading and writing +to the new register. The feature is only available in 64-bit mode, +even though there is theoretically space in the PAE PTEs. These +permissions are enforced on data access only and have no effect on +instruction fetches. + +The kernel attempts to make protection keys consistent with the +behavior of a plain mprotect(). For instance if you do this: + + mprotect(ptr, size, PROT_NONE); + something(ptr); + +you can expect the same effects with protection keys when doing this: + + mprotect(ptr, size, PROT_READ|PROT_WRITE); + set_pkey(ptr, size, 4); + wrpkru(0xffffff3f); // access disable pkey 4 + something(ptr); + +That should be true whether something() is a direct access to 'ptr' +like: + + *ptr = foo; + +or when the kernel does the access on the application's behalf like +with a read(): + + read(fd, ptr, 1); + +The kernel will send a SIGSEGV in both cases, but si_code will be set +to SEGV_PKERR when violating protection keys versus SEGV_ACCERR when +the plain mprotect() permissions are violated. + +========= + +Changes in v005: + * completed "software enforcement of PKEYs" + * fixed a ton of bugs + +Changes in v004: + * bunch of code updates including working signal handling + +Changes in v003: + * update to new FPU code, and add a bunch of XSAVE patches + to the beginning + +Changes in v002: + + * make mprotect() actually work + + _ -- To unsubscribe, send a message with 'unsubscribe linux-mm' in the body to majordomo@xxxxxxxxx. For more info on Linux MM, see: http://www.linux-mm.org/ . Don't email: <a href=mailto:"dont@xxxxxxxxx";> email@xxxxxxxxx </a>