Add a new debug module param 'debug_intercept_exceptions' which will allow the KVM to intercept any guest exception, and forward it to the guest.
This can be very useful for guest debugging and/or KVM debugging with kvm trace. This is not intended to be used on production systems. This is based on an idea first shown here: https://patchwork.kernel.org/project/kvm/patch/20160301192822.gd22...@pd.tnic/ CC: Borislav Petkov <b...@suse.de> Signed-off-by: Maxim Levitsky <mlevi...@redhat.com> --- arch/x86/include/asm/kvm_host.h | 2 + arch/x86/kvm/svm/svm.c | 77 ++++++++++++++++++++++++++++++++- arch/x86/kvm/svm/svm.h | 5 ++- arch/x86/kvm/x86.c | 5 ++- 4 files changed, 85 insertions(+), 4 deletions(-) diff --git a/arch/x86/include/asm/kvm_host.h b/arch/x86/include/asm/kvm_host.h index a52f973bdff6d..c8f44a88b3153 100644 --- a/arch/x86/include/asm/kvm_host.h +++ b/arch/x86/include/asm/kvm_host.h @@ -1564,6 +1564,8 @@ int kvm_emulate_rdpmc(struct kvm_vcpu *vcpu); void kvm_queue_exception(struct kvm_vcpu *vcpu, unsigned nr); void kvm_queue_exception_e(struct kvm_vcpu *vcpu, unsigned nr, u32 error_code); void kvm_queue_exception_p(struct kvm_vcpu *vcpu, unsigned nr, unsigned long payload); +void kvm_queue_exception_e_p(struct kvm_vcpu *vcpu, unsigned nr, + u32 error_code, unsigned long payload); void kvm_requeue_exception(struct kvm_vcpu *vcpu, unsigned nr); void kvm_requeue_exception_e(struct kvm_vcpu *vcpu, unsigned nr, u32 error_code); void kvm_inject_page_fault(struct kvm_vcpu *vcpu, struct x86_exception *fault); diff --git a/arch/x86/kvm/svm/svm.c b/arch/x86/kvm/svm/svm.c index 271196400495f..94156a367a663 100644 --- a/arch/x86/kvm/svm/svm.c +++ b/arch/x86/kvm/svm/svm.c @@ -197,6 +197,9 @@ module_param(sev_es, int, 0444); bool __read_mostly dump_invalid_vmcb; module_param(dump_invalid_vmcb, bool, 0644); +uint debug_intercept_exceptions; +module_param(debug_intercept_exceptions, uint, 0444); + static bool svm_gp_erratum_intercept = true; static u8 rsm_ins_bytes[] = "\x0f\xaa"; @@ -220,6 +223,8 @@ static const u32 msrpm_ranges[] = {0, 0xc0000000, 0xc0010000}; #define MSRS_RANGE_SIZE 2048 #define MSRS_IN_RANGE (MSRS_RANGE_SIZE * 8 / 2) +static void init_debug_exceptions_intercept(struct vcpu_svm *svm); + u32 svm_msrpm_offset(u32 msr) { u32 offset; @@ -1137,6 +1142,8 @@ static void init_vmcb(struct kvm_vcpu *vcpu) set_exception_intercept(svm, MC_VECTOR); set_exception_intercept(svm, AC_VECTOR); set_exception_intercept(svm, DB_VECTOR); + + init_debug_exceptions_intercept(svm); /* * Guest access to VMware backdoor ports could legitimately * trigger #GP because of TSS I/O permission bitmap. @@ -1913,6 +1920,17 @@ static int pf_interception(struct kvm_vcpu *vcpu) u64 fault_address = svm->vmcb->control.exit_info_2; u64 error_code = svm->vmcb->control.exit_info_1; + if ((debug_intercept_exceptions & (1 << PF_VECTOR))) + if (npt_enabled && !vcpu->arch.apf.host_apf_flags) { + /* If #PF was only intercepted for debug, inject + * it directly to the guest, since the mmu code + * is not ready to deal with such page faults + */ + kvm_queue_exception_e_p(vcpu, PF_VECTOR, + error_code, fault_address); + return 1; + } + return kvm_handle_page_fault(vcpu, error_code, fault_address, static_cpu_has(X86_FEATURE_DECODEASSISTS) ? svm->vmcb->control.insn_bytes : NULL, @@ -3025,7 +3043,7 @@ static int invpcid_interception(struct kvm_vcpu *vcpu) return kvm_handle_invpcid(vcpu, type, gva); } -static int (*const svm_exit_handlers[])(struct kvm_vcpu *vcpu) = { +static int (*svm_exit_handlers[])(struct kvm_vcpu *vcpu) = { [SVM_EXIT_READ_CR0] = cr_interception, [SVM_EXIT_READ_CR3] = cr_interception, [SVM_EXIT_READ_CR4] = cr_interception, @@ -3099,6 +3117,63 @@ static int (*const svm_exit_handlers[])(struct kvm_vcpu *vcpu) = { [SVM_EXIT_VMGEXIT] = sev_handle_vmgexit, }; +static int generic_exception_interception(struct kvm_vcpu *vcpu) +{ + /* + * Generic exception handler which forwards a guest exception + * as-is to the guest. + * For exceptions that don't have a special intercept handler. + * + * Used for 'debug_intercept_exceptions' KVM debug feature only. + */ + struct vcpu_svm *svm = to_svm(vcpu); + int exc = svm->vmcb->control.exit_code - SVM_EXIT_EXCP_BASE; + + WARN_ON(exc < 0 || exc > 31); + + if (exc == TS_VECTOR) { + /* + * SVM doesn't provide us with an error code to be able to + * re-inject the #TS exception, so just disable its + * interception, and let the guest re-execute the instruction. + */ + vmcb_clr_intercept(&svm->vmcb01.ptr->control, + INTERCEPT_EXCEPTION_OFFSET + TS_VECTOR); + recalc_intercepts(svm); + return 1; + } else if (exc == DF_VECTOR) { + /* SVM doesn't provide us with an error code for the #DF */ + kvm_queue_exception_e(vcpu, exc, 0); + return 1; + } + + if (x86_exception_has_error_code(exc)) + kvm_queue_exception_e(vcpu, exc, svm->vmcb->control.exit_info_1); + else + kvm_queue_exception(vcpu, exc); + return 1; +} + +static void init_debug_exceptions_intercept(struct vcpu_svm *svm) +{ + int exc; + + for (exc = 0 ; exc < 32 ; exc++) { + if (!(debug_intercept_exceptions & (1 << exc))) + continue; + + /* Those are defined to have undefined behavior in the SVM spec */ + if (exc == 2 || exc == 9) + continue; + + set_exception_intercept(svm, exc); + + if (!svm_exit_handlers[SVM_EXIT_EXCP_BASE + exc]) + svm_exit_handlers[SVM_EXIT_EXCP_BASE + exc] = + generic_exception_interception; + } +} + static void dump_vmcb(struct kvm_vcpu *vcpu) { struct vcpu_svm *svm = to_svm(vcpu); diff --git a/arch/x86/kvm/svm/svm.h b/arch/x86/kvm/svm/svm.h index 8e276c4fb33df..e0ff9ca996df8 100644 --- a/arch/x86/kvm/svm/svm.h +++ b/arch/x86/kvm/svm/svm.h @@ -32,6 +32,7 @@ static const u32 host_save_user_msrs[] = { #define MSRPM_OFFSETS 16 extern u32 msrpm_offsets[MSRPM_OFFSETS] __read_mostly; extern bool npt_enabled; +extern uint debug_intercept_exceptions; enum { VMCB_INTERCEPTS, /* Intercept vectors, TSC offset, @@ -333,7 +334,9 @@ static inline void clr_exception_intercept(struct vcpu_svm *svm, u32 bit) struct vmcb *vmcb = svm->vmcb01.ptr; WARN_ON_ONCE(bit >= 32); - vmcb_clr_intercept(&vmcb->control, INTERCEPT_EXCEPTION_OFFSET + bit); + + if (!((1 << bit) & debug_intercept_exceptions)) + vmcb_clr_intercept(&vmcb->control, INTERCEPT_EXCEPTION_OFFSET + bit); recalc_intercepts(svm); } diff --git a/arch/x86/kvm/x86.c b/arch/x86/kvm/x86.c index b75d990fcf12b..be509944622bd 100644 --- a/arch/x86/kvm/x86.c +++ b/arch/x86/kvm/x86.c @@ -627,12 +627,13 @@ void kvm_queue_exception_p(struct kvm_vcpu *vcpu, unsigned nr, } EXPORT_SYMBOL_GPL(kvm_queue_exception_p); -static void kvm_queue_exception_e_p(struct kvm_vcpu *vcpu, unsigned nr, - u32 error_code, unsigned long payload) +void kvm_queue_exception_e_p(struct kvm_vcpu *vcpu, unsigned nr, + u32 error_code, unsigned long payload) { kvm_multiple_exception(vcpu, nr, true, error_code, true, payload, false); } +EXPORT_SYMBOL_GPL(kvm_queue_exception_e_p); int kvm_complete_insn_gp(struct kvm_vcpu *vcpu, int err) { -- 2.26.2
