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

Greg Kroah-Hartman
2015-10-23T17:47:29Z

From: Paolo Bonzini <pbonzini@redhat.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@redhat.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.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)