From a929bee0e65296ee565251316dc53f1c6b79084a Mon Sep 17 00:00:00 2001 From: Andrew Cooper Date: Wed, 20 Jan 2016 13:58:07 +0100 Subject: [PATCH] x86/vmx: Fix injection of #DB traps following XSA-156 Most #DB exceptions are traps rather than faults, meaning that the instruction pointer in the exception frame points after the instruction rather than at it. However, VMX intercepts all have fault semantics, even when intercepting a trap. Re-injecting an intercepted trap as a fault causes an infinite loop in the guest, by re-executing the same trapping instruction repeatedly. This breaks debugging inside the guest. Introduce a helper which copies VM_EXIT_INTR_INTO to VM_ENTRY_INTR_INFO, and use it to mirror the intercepted interrupt back to the guest. Signed-off-by: Andrew Cooper Acked-by: Kevin Tian master commit: 0747bc8b4d85f3fc0ee1e58418418fa0229e8ff8 master date: 2016-01-05 11:28:56 +0000 --- xen/arch/x86/hvm/vmx/vmx.c | 32 +++++++++++++++++++++++++++++--- 1 file changed, 29 insertions(+), 3 deletions(-) diff --git a/xen/arch/x86/hvm/vmx/vmx.c b/xen/arch/x86/hvm/vmx/vmx.c index f78dc9d5e4..404dcfe5ab 100644 --- a/xen/arch/x86/hvm/vmx/vmx.c +++ b/xen/arch/x86/hvm/vmx/vmx.c @@ -2800,6 +2800,33 @@ static int vmx_handle_eoi_write(void) return 0; } +/* + * Propagate VM_EXIT_INTR_INFO to VM_ENTRY_INTR_INFO. Used to mirror an + * intercepted exception back to the guest as if Xen hadn't intercepted it. + * + * It is the callers responsibility to ensure that this function is only used + * in the context of an appropriate vmexit. + */ +static void vmx_propagate_intr(void) +{ + unsigned long intr, tmp; + + __vmread(VM_EXIT_INTR_INFO, &intr); + + ASSERT(intr & INTR_INFO_VALID_MASK); + + __vmwrite(VM_ENTRY_INTR_INFO, intr); + + if ( intr & INTR_INFO_DELIVER_CODE_MASK ) + { + __vmread(VM_EXIT_INTR_ERROR_CODE, &tmp); + __vmwrite(VM_ENTRY_EXCEPTION_ERROR_CODE, tmp); + } + + __vmread(VM_EXIT_INSTRUCTION_LEN, &tmp); + __vmwrite(VM_ENTRY_INSTRUCTION_LEN, tmp); +} + static void vmx_idtv_reinject(unsigned long idtv_info) { @@ -3048,7 +3075,7 @@ void vmx_vmexit_handler(struct cpu_user_regs *regs) HVMTRACE_1D(TRAP_DEBUG, exit_qualification); write_debugreg(6, exit_qualification | DR_STATUS_RESERVED_ONE); if ( !v->domain->debugger_attached ) - hvm_inject_hw_exception(vector, HVM_DELIVER_NO_ERROR_CODE); + vmx_propagate_intr(); else domain_pause_for_debugger(); break; @@ -3117,8 +3144,7 @@ void vmx_vmexit_handler(struct cpu_user_regs *regs) break; case TRAP_alignment_check: HVMTRACE_1D(TRAP, vector); - __vmread(VM_EXIT_INTR_ERROR_CODE, &ecode); - hvm_inject_hw_exception(vector, ecode); + vmx_propagate_intr(); break; case TRAP_nmi: if ( MASK_EXTR(intr_info, INTR_INFO_INTR_TYPE_MASK) !=