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During fuzzing a kernel driver via WTF fuzzer with bochscpu backend for one case I got #GP (--> nt!KiGeneralProtectionFault() ) on the instruction:
fffff8062804a378 0f22e0 mov cr4,rax

Inside nt!KiFlushCurrentTbWorker():

I caught the reason in the debug build of bochs: check_CR4(): write of 0x00350e78 not supported (allowMask=0x3727ff)
(https://sourceforge.net/p/bochs/code/HEAD/tree/trunk/bochs/cpu/crregs.cc#l1273)

Decoded:
001101110010011111111111 - allowed mask
001101010000111001111000 - new value

11 bit is important for now:
// [11] UMIP: User Mode Instruction Prevention R/W
(https://sourceforge.net/p/bochs/code/HEAD/tree/trunk/bochs/cpu/crregs.cc#l1172)

And this bit isn't set:

  if (is_cpu_extension_supported(BX_ISA_UMIP))
    allowMask |= BX_CR4_UMIP_MASK;

(https://sourceforge.net/p/bochs/code/HEAD/tree/trunk/bochs/cpu/crregs.cc#l1251)

The flag BX_ISA_UMIP is set (enable_cpu_extension(BX_ISA_UMIP);) for 3 CPU profiles:

• corei3_cnl (https://sourceforge.net/p/bochs/code/HEAD/tree/trunk/bochs/cpu/cpudb/intel/corei3_cnl.cc#l116)
• corei7_icelake-u (https://sourceforge.net/p/bochs/code/HEAD/tree/trunk/bochs/cpu/cpudb/intel/corei7_icelake-u.cc#l130)
• tigerlake (https://sourceforge.net/p/bochs/code/HEAD/tree/trunk/bochs/cpu/cpudb/intel/tigerlake.cc#l134)

Inside this project the CPU profile selection is simulated in the sim_get_param_enum() function, which uses PARAMS_ENUM with "cpu.model" key:

According to this part, the hardcoded value of 24 always means "corei7_skylake_x", which does not support UMIP.
I think it would be nice to sync with the actual cpudb.h and return the value 27 for the latest CPU profile (tigerlake):
https://sourceforge.net/p/bochs/code/HEAD/tree/trunk/bochs/cpudb.h#l55

While investigating 0vercl0k/wtf#140, I found that suspicious piece of code in mod.rs which seems like a bug..?:

    pub unsafe fn set_state(&self, s: &State) {
        // ...
        self.set_mxcsr(s.mxcsr);
        self.set_mxcsr_mask(s.mxcsr);
    }

Hello,
I encountered this error with rust 1.54

error[E0557]: feature has been removed
 --> vendor\bochscpu\src\lib.rs:1:12
  |
1 | #![feature(unwind_attributes)]
  |            ^^^^^^^^^^^^^^^^^ feature has been removed
  |
  = note: use the C-unwind ABI instead

I guess it's related to rust-lang/rfcs#2945