> 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? > > 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. Alternately, I did work on a Wine patch to emulate the UMIP instructions in user-space, but it adds a lot of code and I don’t think there’s much appetite for it in upstream Wine (especially since the kernel emulation is sufficient for almost all cases). https://www.winehq.org/pipermail/wine-devel/2020-February/160027.html In the meantime, an easy way to disable UMIP without rebuilding the kernel is to pass 'clearcpuid=514’ on the kernel command line. Brendan Shanks CodeWeavers
