KVM_SET_XCRS failed: Invalid argument

[xupeng1231]

Hello, I try to use the hevd example according to the instruction, however when I runing the fuzzing node with the kvm backend, the KVM_SET_XCRS failed with Invalid argument error.
I use the kvm version 12, and I carry out the expriment in Ubuntu 20.04. Do you know the reason about this failure.

[0vercl0k]

Can you share your regs.json?

I've seen this before it means that the VM where I took the dump had bits in xcr0 that are not supported in the environment you're loading it in; based on my experience it's usually the bits that enable AVX512 or some of those.

Cheers

[xupeng1231]

the regs.json is as follow, I used the regs.json that come from you hevd example, the value of xcr0 is 0xe7. Do you know how to solve the problem, and is there any material that explain about this area? {"rax":"0xdfd98ff3d0","rbx":"0x88","rcx":"0x88","rdx":"0xdeadbeef","rsi":"0x0","rdi":"0x0","rip":"0x7ff6f5bb111e","rsp":"0xdfd98ff380","rbp":"0x0","r8":"0xdfd98ff3d0","r9":"0x400","r10":"0x2263e823055","r11":"0x7ff6f5bcb54d","r12":"0x0","r13":"0x0","r14":"0x0","r15":"0x0","rflags":"0x206","dr0":"0x0","dr1":"0x0","dr2":"0x0","dr3":"0x0","dr6":"0xffff4ff0","dr7":"0x400","es":{"present":true,"selector":"0x2b","base":"0x0","limit":"0xffffffff","attr":"0xcf3"},"cs":{"present":true,"selector":"0x33","base":"0x0","limit":"0x0","attr":"0x22fb"},"ss":{"present":true,"selector":"0x2b","base":"0x0","limit":"0xffffffff","attr":"0xcf3"},"ds":{"present":true,"selector":"0x2b","base":"0x0","limit":"0xffffffff","attr":"0xcf3"},"fs":{"present":true,"selector":"0x53","base":"0x0","limit":"0x3c00","attr":"0x4f3"},"gs":{"present":true,"selector":"0x2b","base":"0xdfd9621000","limit":"0xffffffff","attr":"0xcf3"},"tr":{"present":true,"selector":"0x40","base":"0xfffff8047375c000","limit":"0x67","attr":"0x8b"},"ldtr":{"present":false,"selector":"0x0","base":"0x0","limit":"0x0","attr":"0x0"},"tsc":"0x2531558129a","apic_base":"0xfee00900","sysenter_cs":"0x0","sysenter_esp":"0x0","sysenter_eip":"0x0","pat":"0x7010600070106","efer":"0xd01","star":"0x23001000000000","lstar":"0xfffff8046f1cdc40","cstar":"0xfffff8046f1cd780","sfmask":"0x4700","kernel_gs_base":"0xfffff8046b6f3000","tsc_aux":"0x0","fpcw":"0x27f","fpsw":"0x0","fptw":"0x0","fpst":["0x-Infinity","0x-Infinity","0x-Infinity","0x-Infinity","0x-Infinity","0x-Infinity","0x-Infinity","0x-Infinity"],"mxcsr":"0x1f80","cr0":"0x80050033","cr2":"0x7ff6f5bbed4c","cr3":"0x101ba2000","cr4":"0x3506f8","cr8":"0x0","xcr0":"0xe7","gdtr":{"base":"0xfffff8047375dfb0","limit":"0x57"},"idtr":{"base":"0xfffff8047375b000","limit":"0xfff"},"mxcsr_mask":"0x0","fpop":"0x0"}

[0vercl0k]

Oh sorry I missed the fact you were using the file from the hevd example 🤦🏽‍♂️

Can you try to change the value of xcr0 from 0xe7 to 0x7 and try it again please?

Cheers

[xupeng1231]

Thank you very much. After changing the value of xcr0 from 0xe7 to 0x7, it works well.
Furthermore, your this work(wtf) is really cool and efficient. I will study it systematically. I didn't know much about kvm and virtualization, can you recommend some learning materials related to your system.

[0vercl0k]

Awesome!

Thanks for the kind words 🙏🏽 The best references for me were:

• firecracker's code as it uses internally the same APIs that wtf uses,
• The Definitive KVM (Kernel-based Virtual Machine) API Documentation.

Cheers