lguest: fix guest crash on non-linear addresses in gdt pvops

Fixes guest crash 'lguest: bad read address 0x4800000 len 256'

The new per-cpu allocator ends up handing a non-linear address to
write_gdt_entry.  We do __pa() on it, and hand it to the host, which
kills us.

I've long wanted to make the hypercall "LOAD_GDT_ENTRY" to match the IDT
code, but had no pressing reason until now.

Signed-off-by: Rusty Russell <rusty@rustcorp.com.au>
Cc: lguest@ozlabs.org

2 files changed, 10 insertions, 8 deletions

diff --git a/arch/x86/include/asm/lguest_hcall.h b/arch/x86/include/asm/lguest_hcall.h
index 0f4ee7148af..faae1996487 100644
--- a/arch/x86/include/asm/lguest_hcall.h
+++ b/arch/x86/include/asm/lguest_hcall.h
@@ -5,7 +5,6 @@
 #define LHCALL_FLUSH_ASYNC	0
 #define LHCALL_LGUEST_INIT	1
 #define LHCALL_SHUTDOWN		2
-#define LHCALL_LOAD_GDT		3
 #define LHCALL_NEW_PGTABLE	4
 #define LHCALL_FLUSH_TLB	5
 #define LHCALL_LOAD_IDT_ENTRY	6
@@ -17,6 +16,7 @@
 #define LHCALL_SET_PMD		15
 #define LHCALL_LOAD_TLS		16
 #define LHCALL_NOTIFY		17
+#define LHCALL_LOAD_GDT_ENTRY	18
 
 #define LGUEST_TRAP_ENTRY 0x1F
 
diff --git a/arch/x86/lguest/boot.c b/arch/x86/lguest/boot.c
index e94a11e42f9..a2085368a3d 100644
--- a/arch/x86/lguest/boot.c
+++ b/arch/x86/lguest/boot.c
@@ -273,15 +273,15 @@ static void lguest_load_idt(const struct desc_ptr *desc)
  * controls the entire thing and the Guest asks it to make changes using the
  * LOAD_GDT hypercall.
  *
- * This is the opposite of the IDT code where we have a LOAD_IDT_ENTRY
- * hypercall and use that repeatedly to load a new IDT.  I don't think it
- * really matters, but wouldn't it be nice if they were the same?  Wouldn't
- * it be even better if you were the one to send the patch to fix it?
+ * This is the exactly like the IDT code.
  */
 static void lguest_load_gdt(const struct desc_ptr *desc)
 {
-	BUG_ON((desc->size + 1) / 8 != GDT_ENTRIES);
-	kvm_hypercall2(LHCALL_LOAD_GDT, __pa(desc->address), GDT_ENTRIES);
+	unsigned int i;
+	struct desc_struct *gdt = (void *)desc->address;
+
+	for (i = 0; i < (desc->size+1)/8; i++)
+		kvm_hypercall3(LHCALL_LOAD_GDT_ENTRY, i, gdt[i].a, gdt[i].b);
 }
 
 /* For a single GDT entry which changes, we do the lazy thing: alter our GDT,
@@ -291,7 +291,9 @@ static void lguest_write_gdt_entry(struct desc_struct *dt, int entrynum,
 				   const void *desc, int type)
 {
 	native_write_gdt_entry(dt, entrynum, desc, type);
-	kvm_hypercall2(LHCALL_LOAD_GDT, __pa(dt), GDT_ENTRIES);
+	/* Tell Host about this new entry. */
+	kvm_hypercall3(LHCALL_LOAD_GDT_ENTRY, entrynum,
+		       dt[entrynum].a, dt[entrynum].b);
 }
 
 /* OK, I lied.  There are three "thread local storage" GDT entries which change