KVM: x86: Access to LDT/GDT that wraparound is incorrect
When access to descriptor in LDT/GDT wraparound outside long-mode, the address
of the descriptor should be truncated to 32-bit. Citing Intel SDM 2.1.1.1
"Global and Local Descriptor Tables in IA-32e Mode": "GDTR and LDTR registers
are expanded to 64-bits wide in both IA-32e sub-modes (64-bit mode and
compatibility mode)."
So in other cases, we need to truncate. Creating new function to return a
pointer to descriptor table to avoid too much code duplication.
Signed-off-by: Nadav Amit <namit@cs.technion.ac.il>
[Wrap 64-bit check with #ifdef CONFIG_X86_64, to avoid a "right shift count
>= width of type" warning and consequent undefined behavior. - Paolo]
Signed-off-by: Paolo Bonzini <pbonzini@redhat.com>
diff --git a/arch/x86/kvm/emulate.c b/arch/x86/kvm/emulate.c
index e36e1fc..d949287 100644
--- a/arch/x86/kvm/emulate.c
+++ b/arch/x86/kvm/emulate.c
@@ -1444,28 +1444,8 @@
ops->get_gdt(ctxt, dt);
}
-/* allowed just for 8 bytes segments */
-static int read_segment_descriptor(struct x86_emulate_ctxt *ctxt,
- u16 selector, struct desc_struct *desc,
- ulong *desc_addr_p)
-{
- struct desc_ptr dt;
- u16 index = selector >> 3;
- ulong addr;
-
- get_descriptor_table_ptr(ctxt, selector, &dt);
-
- if (dt.size < index * 8 + 7)
- return emulate_gp(ctxt, selector & 0xfffc);
-
- *desc_addr_p = addr = dt.address + index * 8;
- return ctxt->ops->read_std(ctxt, addr, desc, sizeof *desc,
- &ctxt->exception);
-}
-
-/* allowed just for 8 bytes segments */
-static int write_segment_descriptor(struct x86_emulate_ctxt *ctxt,
- u16 selector, struct desc_struct *desc)
+static int get_descriptor_ptr(struct x86_emulate_ctxt *ctxt,
+ u16 selector, ulong *desc_addr_p)
{
struct desc_ptr dt;
u16 index = selector >> 3;
@@ -1477,6 +1457,47 @@
return emulate_gp(ctxt, selector & 0xfffc);
addr = dt.address + index * 8;
+
+#ifdef CONFIG_X86_64
+ if (addr >> 32 != 0) {
+ u64 efer = 0;
+
+ ctxt->ops->get_msr(ctxt, MSR_EFER, &efer);
+ if (!(efer & EFER_LMA))
+ addr &= (u32)-1;
+ }
+#endif
+
+ *desc_addr_p = addr;
+ return X86EMUL_CONTINUE;
+}
+
+/* allowed just for 8 bytes segments */
+static int read_segment_descriptor(struct x86_emulate_ctxt *ctxt,
+ u16 selector, struct desc_struct *desc,
+ ulong *desc_addr_p)
+{
+ int rc;
+
+ rc = get_descriptor_ptr(ctxt, selector, desc_addr_p);
+ if (rc != X86EMUL_CONTINUE)
+ return rc;
+
+ return ctxt->ops->read_std(ctxt, *desc_addr_p, desc, sizeof(*desc),
+ &ctxt->exception);
+}
+
+/* allowed just for 8 bytes segments */
+static int write_segment_descriptor(struct x86_emulate_ctxt *ctxt,
+ u16 selector, struct desc_struct *desc)
+{
+ int rc;
+ ulong addr;
+
+ rc = get_descriptor_ptr(ctxt, selector, &addr);
+ if (rc != X86EMUL_CONTINUE)
+ return rc;
+
return ctxt->ops->write_std(ctxt, addr, desc, sizeof *desc,
&ctxt->exception);
}