我正在尝试在虚拟环境中调试rootkit。通过反转，我知道它使用了 super 简单的CPU时序检查，看起来像这样(source pafish):
static inline unsigned long long rdtsc_diff_vmexit() {
unsigned long long ret, ret2;
unsigned eax, edx;
__asm__ volatile("rdtsc" : "=a" (eax), "=d" (edx));
ret = ((unsigned long long)eax) | (((unsigned long long)edx) << 32);
/* vm exit forced here. it uses: eax = 0; cpuid; */
__asm__ volatile("cpuid" : /* no output */ : "a"(0x00));
/**/
__asm__ volatile("rdtsc" : "=a" (eax), "=d" (edx));
ret2 = ((unsigned long long)eax) | (((unsigned long long)edx) << 32);
return ret2 - ret;
}
int cpu_rdtsc() {
int i;
unsigned long long avg = 0;
for (i = 0; i < 10; i++) {
avg = avg + rdtsc_diff();
Sleep(500);
}
avg = avg / 10;
return (avg < 750 && avg > 0) ? FALSE : TRUE;
}
正如this question(和mailing list)中所述，我克隆了Linux内核源代码(5.4.0稳定版)并相应地编辑了以下文件:
arch/x86/kvm/vmx/vmx.c(大约2300，setup_vmcs_config):
min = CPU_BASED_HLT_EXITING |
#ifdef CONFIG_X86_64
CPU_BASED_CR8_LOAD_EXITING |
CPU_BASED_CR8_STORE_EXITING |
#endif
CPU_BASED_CR3_LOAD_EXITING |
CPU_BASED_CR3_STORE_EXITING |
CPU_BASED_UNCOND_IO_EXITING |
CPU_BASED_MOV_DR_EXITING |
CPU_BASED_USE_TSC_OFFSETTING |
CPU_BASED_MWAIT_EXITING |
CPU_BASED_MONITOR_EXITING |
CPU_BASED_INVLPG_EXITING |
CPU_BASED_RDPMC_EXITING |
CPU_BASED_RDTSC_EXITING; // <- added this
opt = CPU_BASED_TPR_SHADOW |
CPU_BASED_USE_MSR_BITMAPS |
CPU_BASED_ACTIVATE_SECONDARY_CONTROLS;
if (adjust_vmx_controls(min, opt, MSR_IA32_VMX_PROCBASED_CTLS,
&_cpu_based_exec_control) < 0)
return -EIO;
static int (*kvm_vmx_exit_handlers[])(struct kvm_vcpu *vcpu) = {
[EXIT_REASON_EXCEPTION_NMI] = handle_exception_nmi,
[EXIT_REASON_EXTERNAL_INTERRUPT] = handle_external_interrupt,
[EXIT_REASON_TRIPLE_FAULT] = handle_triple_fault,
[EXIT_REASON_NMI_WINDOW] = handle_nmi_window,
[EXIT_REASON_IO_INSTRUCTION] = handle_io,
[EXIT_REASON_CR_ACCESS] = handle_cr,
[EXIT_REASON_DR_ACCESS] = handle_dr,
[EXIT_REASON_CPUID] = kvm_emulate_cpuid,
[EXIT_REASON_MSR_READ] = kvm_emulate_rdmsr,
[EXIT_REASON_MSR_WRITE] = kvm_emulate_wrmsr,
[EXIT_REASON_INTERRUPT_WINDOW] = handle_interrupt_window,
[EXIT_REASON_HLT] = kvm_emulate_halt,
[EXIT_REASON_INVD] = handle_invd,
[EXIT_REASON_INVLPG] = handle_invlpg,
[EXIT_REASON_RDPMC] = handle_rdpmc,
[EXIT_REASON_VMCALL] = handle_vmcall,
[EXIT_REASON_VMCLEAR] = handle_vmx_instruction,
[EXIT_REASON_VMLAUNCH] = handle_vmx_instruction,
[EXIT_REASON_VMPTRLD] = handle_vmx_instruction,
[EXIT_REASON_VMPTRST] = handle_vmx_instruction,
[EXIT_REASON_VMREAD] = handle_vmx_instruction,
[EXIT_REASON_VMRESUME] = handle_vmx_instruction,
[EXIT_REASON_VMWRITE] = handle_vmx_instruction,
[EXIT_REASON_VMOFF] = handle_vmx_instruction,
[EXIT_REASON_VMON] = handle_vmx_instruction,
[EXIT_REASON_TPR_BELOW_THRESHOLD] = handle_tpr_below_threshold,
[EXIT_REASON_APIC_ACCESS] = handle_apic_access,
[EXIT_REASON_APIC_WRITE] = handle_apic_write,
[EXIT_REASON_EOI_INDUCED] = handle_apic_eoi_induced,
[EXIT_REASON_WBINVD] = handle_wbinvd,
[EXIT_REASON_XSETBV] = handle_xsetbv,
[EXIT_REASON_TASK_SWITCH] = handle_task_switch,
[EXIT_REASON_MCE_DURING_VMENTRY] = handle_machine_check,
[EXIT_REASON_GDTR_IDTR] = handle_desc,
[EXIT_REASON_LDTR_TR] = handle_desc,
[EXIT_REASON_EPT_VIOLATION] = handle_ept_violation,
[EXIT_REASON_EPT_MISCONFIG] = handle_ept_misconfig,
[EXIT_REASON_PAUSE_INSTRUCTION] = handle_pause,
[EXIT_REASON_MWAIT_INSTRUCTION] = handle_mwait,
[EXIT_REASON_MONITOR_TRAP_FLAG] = handle_monitor_trap,
[EXIT_REASON_MONITOR_INSTRUCTION] = handle_monitor,
[EXIT_REASON_INVEPT] = handle_vmx_instruction,
[EXIT_REASON_INVVPID] = handle_vmx_instruction,
[EXIT_REASON_RDRAND] = handle_invalid_op,
[EXIT_REASON_RDSEED] = handle_invalid_op,
[EXIT_REASON_PML_FULL] = handle_pml_full,
[EXIT_REASON_INVPCID] = handle_invpcid,
[EXIT_REASON_VMFUNC] = handle_vmx_instruction,
[EXIT_REASON_PREEMPTION_TIMER] = handle_preemption_timer,
[EXIT_REASON_ENCLS] = handle_encls,
[EXIT_REASON_RDTSC] = handle_rdtsc, // <- added exit handler
};
static int handle_rdtsc(struct kvm_vcpu *vcpu)
{
printk("[vmkernel] handling fake rdtsc from cpl %i\n", vmx_get_cpl(vcpu));
uint64_t data;
data = 123;
vcpu->arch.regs[VCPU_REGS_RAX] = data & -1u;
vcpu->arch.regs[VCPU_REGS_RDX] = (data >> 32) & -1u;
skip_emulated_instruction(vcpu);
return 1;
}
dmesg之后，我什么都看不到。同样，测得的差异完全相同且不变。为了使处理程序真正被调用和使用，我还需要编辑什么？我正在将所有选项都设置为默认值(运行
make menuconfig->保存)来构建内核。当然，我还检查了内核是否已启动以及Qemu是否将KVM用于VM。
任何想法，将不胜感激。谢谢。
最佳答案
好吧，我上面发布的代码可以运行，但是只能在Intel CPU上使用。可悲的是我没有注意到。
要使其在AMD CPU上运行，我需要修改 arch/x86/kvm/svm/svm.c :
static int (*const svm_exit_handlers[])(struct vcpu_svm *svm) = {
[SVM_EXIT_READ_CR0] = cr_interception,
[SVM_EXIT_READ_CR3] = cr_interception,
[SVM_EXIT_READ_CR4] = cr_interception,
[SVM_EXIT_READ_CR8] = cr_interception,
[SVM_EXIT_CR0_SEL_WRITE] = cr_interception,
[SVM_EXIT_WRITE_CR0] = cr_interception,
[SVM_EXIT_WRITE_CR3] = cr_interception,
[SVM_EXIT_WRITE_CR4] = cr_interception,
[SVM_EXIT_WRITE_CR8] = cr8_write_interception,
[SVM_EXIT_READ_DR0] = dr_interception,
[SVM_EXIT_READ_DR1] = dr_interception,
[SVM_EXIT_READ_DR2] = dr_interception,
[SVM_EXIT_READ_DR3] = dr_interception,
[SVM_EXIT_READ_DR4] = dr_interception,
[SVM_EXIT_READ_DR5] = dr_interception,
[SVM_EXIT_READ_DR6] = dr_interception,
[SVM_EXIT_READ_DR7] = dr_interception,
[SVM_EXIT_WRITE_DR0] = dr_interception,
[SVM_EXIT_WRITE_DR1] = dr_interception,
[SVM_EXIT_WRITE_DR2] = dr_interception,
[SVM_EXIT_WRITE_DR3] = dr_interception,
[SVM_EXIT_WRITE_DR4] = dr_interception,
[SVM_EXIT_WRITE_DR5] = dr_interception,
[SVM_EXIT_WRITE_DR6] = dr_interception,
[SVM_EXIT_WRITE_DR7] = dr_interception,
[SVM_EXIT_EXCP_BASE + DB_VECTOR] = db_interception,
[SVM_EXIT_EXCP_BASE + BP_VECTOR] = bp_interception,
[SVM_EXIT_EXCP_BASE + UD_VECTOR] = ud_interception,
[SVM_EXIT_EXCP_BASE + PF_VECTOR] = pf_interception,
[SVM_EXIT_EXCP_BASE + MC_VECTOR] = mc_interception,
[SVM_EXIT_EXCP_BASE + AC_VECTOR] = ac_interception,
[SVM_EXIT_EXCP_BASE + GP_VECTOR] = gp_interception,
[SVM_EXIT_INTR] = intr_interception,
[SVM_EXIT_NMI] = nmi_interception,
[SVM_EXIT_SMI] = nop_on_interception,
[SVM_EXIT_INIT] = nop_on_interception,
[SVM_EXIT_VINTR] = interrupt_window_interception,
[SVM_EXIT_RDPMC] = rdpmc_interception,
[SVM_EXIT_CPUID] = cpuid_interception,
[SVM_EXIT_IRET] = iret_interception,
[SVM_EXIT_INVD] = emulate_on_interception,
[SVM_EXIT_PAUSE] = pause_interception,
[SVM_EXIT_HLT] = halt_interception,
[SVM_EXIT_INVLPG] = invlpg_interception,
[SVM_EXIT_INVLPGA] = invlpga_interception,
[SVM_EXIT_IOIO] = io_interception,
[SVM_EXIT_MSR] = msr_interception,
[SVM_EXIT_TASK_SWITCH] = task_switch_interception,
[SVM_EXIT_SHUTDOWN] = shutdown_interception,
[SVM_EXIT_VMRUN] = vmrun_interception,
[SVM_EXIT_VMMCALL] = vmmcall_interception,
[SVM_EXIT_VMLOAD] = vmload_interception,
[SVM_EXIT_VMSAVE] = vmsave_interception,
[SVM_EXIT_STGI] = stgi_interception,
[SVM_EXIT_CLGI] = clgi_interception,
[SVM_EXIT_SKINIT] = skinit_interception,
[SVM_EXIT_WBINVD] = wbinvd_interception,
[SVM_EXIT_MONITOR] = monitor_interception,
[SVM_EXIT_MWAIT] = mwait_interception,
[SVM_EXIT_XSETBV] = xsetbv_interception,
[SVM_EXIT_RDPRU] = rdpru_interception,
[SVM_EXIT_NPF] = npf_interception,
[SVM_EXIT_RSM] = rsm_interception,
[SVM_EXIT_AVIC_INCOMPLETE_IPI] = avic_incomplete_ipi_interception,
[SVM_EXIT_AVIC_UNACCELERATED_ACCESS] = avic_unaccelerated_access_interception,
[SVM_EXIT_RDTSC] = handle_rdtsc_interception, // added handler
};
set_intercept(svm, INTERCEPT_WBINVD);
set_intercept(svm, INTERCEPT_XSETBV);
set_intercept(svm, INTERCEPT_RDPRU);
set_intercept(svm, INTERCEPT_RSM);
set_intercept(svm, INTERCEPT_RDTSC); // added
if (!kvm_mwait_in_guest(svm->vcpu.kvm)) {
set_intercept(svm, INTERCEPT_MONITOR);
set_intercept(svm, INTERCEPT_MWAIT);
}
static int handle_rdtsc_interception(struct vcpu_svm *svm)
{
printk("[vmkernel] handling fake rdtsc (AMD) from cpl %i\n", svm_get_cpl(&svm->vcpu));
svm->vcpu.arch.regs[VCPU_REGS_RAX] = last_tick & -1u;
svm->vcpu.arch.regs[VCPU_REGS_RDX] = (last_tick >> 32) & -1u;
skip_emulated_instruction(&svm->vcpu);
return 1;
}
关于c - 在KVM中拦截RDTSC指令，我们在Stack Overflow上找到一个类似的问题：https://stackoverflow.com/questions/62970242/