Messages in this thread | | | Date | Tue, 19 May 2020 16:38:15 +0200 | From | Andreas Rammhold <> | Subject | umip: AMD Ryzen 3900X, pagefault after emulate SLDT/SIDT instruction |
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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.
I'd love to contriubte a patch but I have no knowledge of the inner workings of how UMIP actually works.
Is there anything else I can provide to help debugging/fixing this? Very happy to test patches as well.
[example] https://www.aldeid.com/wiki/X86-assembly/Instructions/sldt
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