On Fri, Oct 11, 2019 at 09:11:54AM -0700, Jim Mattson wrote: > On Fri, Oct 11, 2019 at 12:48 AM Yang Weijiang <weijiang.yang@xxxxxxxxx> wrote: > > > > On Thu, Oct 10, 2019 at 02:42:51PM -0700, Jim Mattson wrote: > > > On Tue, Sep 17, 2019 at 1:52 AM Yang Weijiang <weijiang.yang@xxxxxxxxx> wrote: > > > > > > > > EPT-Based Sub-Page write Protection(SPP)is a HW capability which allows > > > > Virtual Machine Monitor(VMM) to specify write-permission for guest > > > > physical memory at a sub-page(128 byte) granularity. When this > > > > capability is enabled, the CPU enforces write-access check for sub-pages > > > > within a 4KB page. > > > > > > > > The feature is targeted to provide fine-grained memory protection for > > > > usages such as device virtualization, memory check-point and VM > > > > introspection etc. > > > > > > > > SPP is active when the "sub-page write protection" (bit 23) is 1 in > > > > Secondary VM-Execution Controls. The feature is backed with a Sub-Page > > > > Permission Table(SPPT), SPPT is referenced via a 64-bit control field > > > > called Sub-Page Permission Table Pointer (SPPTP) which contains a > > > > 4K-aligned physical address. > > > > > > > > To enable SPP for certain physical page, the gfn should be first mapped > > > > to a 4KB entry, then set bit 61 of the corresponding EPT leaf entry. > > > > While HW walks EPT, if bit 61 is set, it traverses SPPT with the guset > > > > physical address to find out the sub-page permissions at the leaf entry. > > > > If the corresponding bit is set, write to sub-page is permitted, > > > > otherwise, SPP induced EPT violation is generated. > > > > > > How do you handle sub-page permissions for instructions emulated by kvm? > > How about checking if the gpa is SPP protected, if it is, inject some > > exception to guest? > The SPP semantics are well-defined. If a kvm-emulated instruction > tries to write to a sub-page that is write-protected, then an > SPP-induced EPT violation should be synthesized. Hi, Jim, Regarding the emulated instructions in KVM, there're quite a few instructions can write guest memory, such as MOVS, XCHG, INS etc., check each destination against SPP protected area would be trivial if deals with them individually, and PIO/MMIO induced vmexit/page_fault also can link to a SPP protected page, e.g., a string instruction's the destination is SPP protected memory. Is there a good way to intercept these writes? emulate_ops.write_emulated() is called in most of the emulation cases to check and write guest memory, but not sure it's suitable. Do you have any suggestion? Thanks!
