On Wed, 2017-03-08 at 07:56 -0800, Andy Lutomirski wrote: > On Tue, Mar 7, 2017 at 4:32 PM, Ricardo Neri > <ricardo.neri-calderon@xxxxxxxxxxxxxxx> wrote: > > Certain user space programs that run on virtual-8086 mode may utilize > > instructions protected by the User-Mode Instruction Prevention (UMIP) > > security feature present in new Intel processors: SGDT, SIDT and SMSW. In > > such a case, a general protection fault is issued if UMIP is enabled. When > > such a fault happens, the kernel catches it and emulates the results of > > these instructions with dummy values. The purpose of this new > > test is to verify whether the impacted instructions can be executed without > > causing such #GP. If no #GP exceptions occur, we expect to exit virtual- > > 8086 mode from INT 0x80. > > > > The instructions protected by UMIP are executed in representative use > > cases: > > a) the memory address of the result is given in the form of a displacement > > from the base of the data segment > > b) the memory address of the result is given in a general purpose register > > c) the result is stored directly in a general purpose register. > > > > Unfortunately, it is not possible to check the results against a set of > > expected values because no emulation will occur in systems that do not have > > the UMIP feature. Instead, results are printed for verification. > > You could pre-initialize the result buffer to a bunch of non-matching > values (1, 2, 3, ...) and then check that all the invocations of the > same instruction gave the same value. Yes, I can do this. Alternatively, I can check in the test program if the CPU has UMIP and only run the tests in that case. > > If you do this, maybe make it a follow-up patch -- see other email. Great! Thank you! Thanks and BR, Ricardo -- To unsubscribe from this list: send the line "unsubscribe linux-msdos" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
