Patch "KVM: x86: fix fixing of hypercalls" has been added to the 4.9-stable tree

This is a note to let you know that I've just added the patch titled

KVM: x86: fix fixing of hypercalls

to the 4.9-stable tree which can be found at:
http://www.kernel.org/git/?p=linux/kernel/git/stable/stable-queue.git;a=summary

The filename of the patch is:
kvm-x86-fix-fixing-of-hypercalls.patch
and it can be found in the queue-4.9 subdirectory.

If you, or anyone else, feels it should not be added to the stable tree, please let <[email protected]> know about it.

From: Dmitry Vyukov <[email protected]>
Date: Tue, 17 Jan 2017 14:51:04 +0100
Subject: KVM: x86: fix fixing of hypercalls

From: Dmitry Vyukov <[email protected]>

[ 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.

---
 arch/x86/kvm/x86.c |    3 ++-
 1 file changed, 2 insertions(+), 1 deletion(-)

@@ -6111,7 +6111,8 @@ static int emulator_fix_hypercall(struct
 
 	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)

Patches currently in stable-queue which might be from [email protected] are

queue-4.9/kvm-x86-fix-fixing-of-hypercalls.patch