Question about intercept debug breakpoint in the Guest OS

Question about intercept debug breakpoint in the Guest OS

[Kai Luo]

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Hi: 
Recently I try to intercept a given kernel address-syscall address,for example- of the guest windows 7 to the hypervisor, I set the exception flag in the EXCEPTION_BITMAP as follows: 
vmcs.c 
void vmx_do_resume(vcpu * v) 
{ 
...... 
unsigned long intercepts = __vmread(EXCEPTION_BITMAP); 
unsigned long mask = (1UL << TRAP_debug); 
intercepts |= mask; 
__vmwrite(EXCEPTION_BITMAP, intercepts) 
v->arch.guest_context.debugreg[0] = [Address of a syscall]; 
v->arch.guest_context.debugreg[7] |= 2; 
...... 
} 
I do reveive the VMexit in the vmx_vmexit_handler in vmx.c then I want to let the guest os keep going as usual without concerning about the debug breakpoint so I set some flags as follows: 
case TRAP_debug: 
...... 
regs->eflags |= X86_EFLAGS_RF; 
exit_qualification = __vmread(EXIT_QUALIFICATION); 
write_debug(6, exit_qualification | 0xffff0ff0); 
...... 
The problem is the guest os seems trapped into an infinite loop and take the full vcpu capacity, I find the RIP in the VCPU stay the same, EFLAGS value of the VCPU is 0x2 and the guest os can't respond to any movement of mouse or keyboard,. 
Do I missed some flag when restoring the guest context?Or there are some other reasons that lead to this issue?Could you give me any suggestions? 

Jone 




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