linux-kernel - [PATCH 31/38] KVM: fix load_guest_segment_descriptor() to return X86EMUL

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Date:	Tue, 16 Feb 2010 12:35:29 +0200
From:	Avi Kivity <avi@...hat.com>
To:	kvm@...r.kernel.org
Cc:	linux-kernel@...r.kernel.org
Subject: [PATCH 31/38] KVM: fix load_guest_segment_descriptor() to return X86EMUL_*

From: Takuya Yoshikawa <yoshikawa.takuya@....ntt.co.jp>

This patch fixes load_guest_segment_descriptor() to return
X86EMUL_PROPAGATE_FAULT when it tries to access the descriptor
table beyond the limit of it: suggested by Marcelo.

I have checked current callers of this helper function,
  - kvm_load_segment_descriptor()
  - kvm_task_switch()
and confirmed that this patch will change nothing in the
upper layers if we do not change the handling of this
return value from load_guest_segment_descriptor().

Next step: Although fixing the kvm_task_switch() to handle the
propagated faults properly seems difficult, and maybe not worth
it because TSS is not used commonly these days, we can fix
kvm_load_segment_descriptor(). By doing so, the injected #GP
becomes possible to be handled by the guest. The only problem
for this is how to differentiate this fault from the page faults
generated by kvm_read_guest_virt(). We may have to split this
function to achive this goal.

Signed-off-by: Takuya Yoshikawa <yoshikawa.takuya@....ntt.co.jp>
Signed-off-by: Marcelo Tosatti <mtosatti@...hat.com>
---
 arch/x86/kvm/x86.c |    2 +-
 1 files changed, 1 insertions(+), 1 deletions(-)

diff --git a/arch/x86/kvm/x86.c b/arch/x86/kvm/x86.c
index 0bf3df5..01f0b03 100644
--- a/arch/x86/kvm/x86.c
+++ b/arch/x86/kvm/x86.c
@@ -4663,7 +4663,7 @@ static int load_guest_segment_descriptor(struct kvm_vcpu *vcpu, u16 selector,

 	if (dtable.limit < index * 8 + 7) {
 		kvm_queue_exception_e(vcpu, GP_VECTOR, selector & 0xfffc);
-		return 1;
+		return X86EMUL_PROPAGATE_FAULT;
 	}
 	return kvm_read_guest_virt(dtable.base + index*8, seg_desc, sizeof(*seg_desc), vcpu);
 }
-- 
1.6.5.3

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