On Tue, May 19, 2020 at 12:43 PM Ricardo Neri <ricardo.neri-calde...@linux.intel.com> wrote: > > On Tue, May 19, 2020 at 11:56:40AM -0700, Brendan Shanks wrote: > > > > > On May 19, 2020, at 7:38 AM, Andreas Rammhold <andi@notmuch.email> wrote: > > > > > > Hi, > > > > > > I've been running into a weird problem with UMIP on a current Ryzen > > > 3900x with kernel 5.6.11 where a process receives a page fault after the > > > kernel handled the SLDT (or SIDT) instruction (emulation). > > > > > > The program I am running is run through WINE in 32bit mode and tries to > > > figure out if it is running in a VMWare machine by comparing the results > > > of SLDT against well known constants (basically as shown in the > > > [example] linked below). > > > > > > In dmesg I see the following log lines: > > >> [99970.004756] umip: Program.exe[3080] ip:4373fb sp:32f3e0: SIDT > > >> instruction cannot be used by applications. > > >> [99970.004757] umip: Program.exe[3080] ip:4373fb sp:32f3e0: For now, > > >> expensive software emulation returns the result. > > >> [99970.004758] umip: Program.exe[3080] ip:437415 sp:32f3e0: SLDT > > >> instruction cannot be used by applications. > > > > > > Following that the process terminates with a page fault: > > >> Unhandled exception: page fault on read access to 0xffffffff in 32-bit > > >> code (0x0000000000437415). > > > > > > Assembly at that address: > > >> 0x0000000000437415: sldt 0xffffffe8(%ebp) > > > > > > Running the same executable on the exact same kernel (and userland) but > > > on a Intel i7-8565U doesn't crash at this point. I am guessing the > > > emulation is supposed to do something different on AMD CPUs? > > I am surprised you don't see it on the Intel processor. Maybe it does > not have UMIP. Do you see umip when you do > > $ grep umip /proc/cpuinfo > > ? > > > > > > On the Ryzen the code executes successfully after setting > > > CONFIG_X86_UMIP=n. > > > > Hi Andreas, > > > > The problem is that the kernel does not emulate/spoof the SLDT instruction, > > only SGDT, SIDT, and SMSW. > > SLDT and STR weren't thought to be commonly used, so emulation/spoofing > > wasn’t added. > > In the last few months I have seen reports of one or two (32-bit) Windows > > games that use SLDT though. > > Can you share more information about the application you’re running? > > > > Maybe the best path is to add kernel emulation/spoofing for SLDT and STR on > > 32 and 64-bit, just to cover all the cases. It should be a pretty simple > > patch, I’ll start working on it. > > I have a patch for this already that I wrote for testing purposes: > > https://github.com/ricardon/tip/commit/1692889cb3f8accb523d44b682458e234b93be50 > > Perhaps it can be used as a starting point? Not sure what the spoofing > value should be, though. Perhaps 0?
Possibly SLDT should return nonzero if there's an LDT. --Andy