Messages in this thread | | | Date | Tue, 19 May 2020 12:43:20 -0700 | From | Ricardo Neri <> | Subject | Re: umip: AMD Ryzen 3900X, pagefault after emulate SLDT/SIDT instruction |
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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?
Thanks and BR, Ricardo
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