[PATCH v2 06/11] KVM: x86: emulator/smm: number of GPRs in the SMRAM image depends on the image format

Maxim Levitsky
2022-06-21T15:09:58Z

On 64 bit host, if the guest doesn't have X86_FEATURE_LM, we would
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@redhat.com>
---
arch/x86/kvm/emulate.c | 4 ++--
1 file changed, 2 insertions(+), 2 deletions(-)

diff --git a/arch/x86/kvm/emulate.c b/arch/x86/kvm/emulate.c
index 002687d17f9364..ce186aebca8e83 100644
--- a/arch/x86/kvm/emulate.c
+++ b/arch/x86/kvm/emulate.c
@@ -2469,7 +2469,7 @@ 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);
@@ -2526,7 +2526,7 @@ static int rsm_load_state_64(struct x86_emulate_ctxt *ctxt,
u16 selector;
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);
--
2.26.3