[PATCH for v4.9 LTS 14/86] KVM: x86: fix fixing of hypercalls

[Levin, Alexander (Sasha Levin)]

From: Dmitry Vyukov <dvyukov@xxxxxxxxxx>

[ Upstream commit ce2e852ecc9a42e4b8dabb46025cfef63209234a ]

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@xxxxxxxxxx>
Cc: Paolo Bonzini <pbonzini@xxxxxxxxxx>
Cc: Radim KrÄmÃÅ <rkrcmar@xxxxxxxxxx>
Cc: Wanpeng Li <wanpeng.li@xxxxxxxxxxx>
Cc: kvm@xxxxxxxxxxxxxxx
Cc: syzkaller@xxxxxxxxxxxxxxxx
Signed-off-by: Radim KrÄmÃÅ <rkrcmar@xxxxxxxxxx>
Signed-off-by: Sasha Levin <alexander.levin@xxxxxxxxxxx>
---
 arch/x86/kvm/x86.c | 3 ++-
 1 file changed, 2 insertions(+), 1 deletion(-)

diff --git a/arch/x86/kvm/x86.c b/arch/x86/kvm/x86.c
index 62cde4f67c72..ab3f00399cbb 100644
--- a/arch/x86/kvm/x86.c
+++ b/arch/x86/kvm/x86.c
@@ -6111,7 +6111,8 @@ 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)
-- 
2.11.0