[PATCH v4 14/23] KVM: x86: smm: number of GPRs in the SMRAM image depends on the image format

[Maxim Levitsky]

On 64 bit host, if the guest doesn't have X86_FEATURE_LM, KVM will
access 16 gprs to 32-bit smram image, causing out-ouf-bound ram
access.

On 32 bit host, the rsm_load_state_64/enter_smm_save_state_64
is compiled out, thus access overflow can't happen.

Fixes: b443183a25ab61 ("KVM: x86: Reduce the number of emulator GPRs to '8' for 32-bit KVM")

Signed-off-by: Maxim Levitsky <mlevitsk@xxxxxxxxxx>
Reviewed-by: Sean Christopherson <seanjc@xxxxxxxxxx>
---
 arch/x86/kvm/emulate.c | 1 +
 arch/x86/kvm/smm.c     | 4 ++--
 2 files changed, 3 insertions(+), 2 deletions(-)

diff --git a/arch/x86/kvm/emulate.c b/arch/x86/kvm/emulate.c
index 5cc3efa0e21c17..ac6fac25ba25d8 100644
--- a/arch/x86/kvm/emulate.c
+++ b/arch/x86/kvm/emulate.c
@@ -2307,6 +2307,7 @@ static int em_lseg(struct x86_emulate_ctxt *ctxt)
 	return rc;
 }
 
+
 static int em_rsm(struct x86_emulate_ctxt *ctxt)
 {
 	if ((ctxt->ops->get_hflags(ctxt) & X86EMUL_SMM_MASK) == 0)
diff --git a/arch/x86/kvm/smm.c b/arch/x86/kvm/smm.c
index 41ca128478fcd4..b290ad14070f72 100644
--- a/arch/x86/kvm/smm.c
+++ b/arch/x86/kvm/smm.c
@@ -382,7 +382,7 @@ static int rsm_load_state_32(struct x86_emulate_ctxt *ctxt,
 	ctxt->eflags =             GET_SMSTATE(u32, smstate, 0x7ff4) | X86_EFLAGS_FIXED;
 	ctxt->_eip =               GET_SMSTATE(u32, smstate, 0x7ff0);
 
-	for (i = 0; i < NR_EMULATOR_GPRS; i++)
+	for (i = 0; i < 8; i++)
 		*reg_write(ctxt, i) = GET_SMSTATE(u32, smstate, 0x7fd0 + i * 4);
 
 	val = GET_SMSTATE(u32, smstate, 0x7fcc);
@@ -438,7 +438,7 @@ static int rsm_load_state_64(struct x86_emulate_ctxt *ctxt,
 	u64 val, cr0, cr3, cr4;
 	int i, r;
 
-	for (i = 0; i < NR_EMULATOR_GPRS; i++)
+	for (i = 0; i < 16; i++)
 		*reg_write(ctxt, i) = GET_SMSTATE(u64, smstate, 0x7ff8 - i * 8);
 
 	ctxt->_eip   = GET_SMSTATE(u64, smstate, 0x7f78);
-- 
2.34.3