Commit ce2e852e authored Jan 17, 2017 by Dmitry Vyukov Committed by Radim Krčmář Jan 17, 2017

KVM: x86: fix fixing of hypercalls



emulator_fix_hypercall() replaces hypercall with vmcall instruction,
but it does not handle GP exception properly when writes the new instruction.
It can return X86EMUL_PROPAGATE_FAULT without setting exception information.
This leads to incorrect emulation and triggers
WARN_ON(ctxt->exception.vector > 0x1f) in x86_emulate_insn()
as discovered by syzkaller fuzzer:

WARNING: CPU: 2 PID: 18646 at arch/x86/kvm/emulate.c:5558
Call Trace:
 warn_slowpath_null+0x2c/0x40 kernel/panic.c:582
 x86_emulate_insn+0x16a5/0x4090 arch/x86/kvm/emulate.c:5572
 x86_emulate_instruction+0x403/0x1cc0 arch/x86/kvm/x86.c:5618
 emulate_instruction arch/x86/include/asm/kvm_host.h:1127 [inline]
 handle_exception+0x594/0xfd0 arch/x86/kvm/vmx.c:5762
 vmx_handle_exit+0x2b7/0x38b0 arch/x86/kvm/vmx.c:8625
 vcpu_enter_guest arch/x86/kvm/x86.c:6888 [inline]
 vcpu_run arch/x86/kvm/x86.c:6947 [inline]

Set exception information when write in emulator_fix_hypercall() fails.

Signed-off-by: Dmitry Vyukov <dvyukov@google.com>
Cc: Paolo Bonzini <pbonzini@redhat.com>
Cc: Radim Krčmář <rkrcmar@redhat.com>
Cc: Wanpeng Li <wanpeng.li@hotmail.com>
Cc: kvm@vger.kernel.org
Cc: syzkaller@googlegroups.com
Signed-off-by: Radim Krčmář <rkrcmar@redhat.com>

parent 1b1973ef

arch/x86/kvm/x86.c

+2 −1

Original line number	Diff line number	Diff line
		@@ -6171,7 +6171,8 @@ static int emulator_fix_hypercall(struct x86_emulate_ctxt *ctxt)

		kvm_x86_ops->patch_hypercall(vcpu, instruction);

		return emulator_write_emulated(ctxt, rip, instruction, 3, NULL);
		return emulator_write_emulated(ctxt, rip, instruction, 3,
		&ctxt->exception);
		}

		static int dm_request_for_irq_injection(struct kvm_vcpu *vcpu)

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