linux-kernel - [PATCH 4.2 39/54] KVM: x86: fix RSM into 64-bit protected mode

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Date:	Fri, 23 Oct 2015 10:45:15 -0700
From:	Greg Kroah-Hartman <gregkh@...uxfoundation.org>
To:	linux-kernel@...r.kernel.org
Cc:	Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
	stable@...r.kernel.org, Paolo Bonzini <pbonzini@...hat.com>
Subject: [PATCH 4.2 39/54] KVM: x86: fix RSM into 64-bit protected mode

4.2-stable review patch.  If anyone has any objections, please let me know.

------------------

From: Paolo Bonzini <pbonzini@...hat.com>

commit b10d92a54dac25a6152f1aa1ffc95c12908035ce upstream.

In order to get into 64-bit protected mode, you need to enable
paging while EFER.LMA=1.  For this to work, CS.L must be 0.
Currently, we load the segments before CR0 and CR4, which means
that if RSM returns into 64-bit protected mode CS.L is already 1
and everything breaks.

Luckily, CS.L=0 is always the case when executing RSM, because it
is forbidden to execute RSM from 64-bit protected mode.  Hence it
is enough to load CR0 and CR4 first, and only then the segments.

Fixes: 660a5d517aaab9187f93854425c4c63f4a09195c
Signed-off-by: Paolo Bonzini <pbonzini@...hat.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@...uxfoundation.org>

---
 arch/x86/kvm/emulate.c |   10 +++++++---
 1 file changed, 7 insertions(+), 3 deletions(-)

--- a/arch/x86/kvm/emulate.c
+++ b/arch/x86/kvm/emulate.c
@@ -2418,7 +2418,7 @@ static int rsm_load_state_64(struct x86_
 	u64 val, cr0, cr4;
 	u32 base3;
 	u16 selector;
-	int i;
+	int i, r;
 
 	for (i = 0; i < 16; i++)
 		*reg_write(ctxt, i) = GET_SMSTATE(u64, smbase, 0x7ff8 - i * 8);
@@ -2460,13 +2460,17 @@ static int rsm_load_state_64(struct x86_
 	dt.address =                GET_SMSTATE(u64, smbase, 0x7e68);
 	ctxt->ops->set_gdt(ctxt, &dt);
 
+	r = rsm_enter_protected_mode(ctxt, cr0, cr4);
+	if (r != X86EMUL_CONTINUE)
+		return r;
+
 	for (i = 0; i < 6; i++) {
-		int r = rsm_load_seg_64(ctxt, smbase, i);
+		r = rsm_load_seg_64(ctxt, smbase, i);
 		if (r != X86EMUL_CONTINUE)
 			return r;
 	}
 
-	return rsm_enter_protected_mode(ctxt, cr0, cr4);
+	return X86EMUL_CONTINUE;
 }
 
 static int em_rsm(struct x86_emulate_ctxt *ctxt)


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