[PATCH 4/4] x86/microcode_amd: Fail attempts to load a 0-length microcode blob.

[Andrew Cooper <andrew.cooper3@citrix.com>]

Coverity ID: 1055319

Coverity identified that when passed a microcode header with a length field of
0, get_ucode_from_buffer_amd() would end up calling memcpy(NULL, data, 0)
which is undefined behaviour.

While Xen's implementation of memcpy will do the correct thing in this case,
any user trying to load a 0 length microcode blob deserves an -EINVAL.

Signed-off-by: Andrew Cooper <andrew.cooper3@citrix.com>
CC: Keir Fraser <keir@xen.org>
CC: Jan Beulich <JBeulich@suse.com>
CC: Suravee Suthikulpanit <suravee.suthikulpanit@amd.com>
CC: Boris Ostrovsky <boris.ostrovsky@oracle.com>
---
 xen/arch/x86/microcode_amd.c |    2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/xen/arch/x86/microcode_amd.c b/xen/arch/x86/microcode_amd.c
index a3ceef8..2c767a9 100644
--- a/xen/arch/x86/microcode_amd.c
+++ b/xen/arch/x86/microcode_amd.c
@@ -202,7 +202,7 @@ static int get_ucode_from_buffer_amd(
         return -EINVAL;
     }
 
-    if ( (off + mpbuf->len) > bufsize )
+    if ( mpbuf->len == 0 || ((off + mpbuf->len) > bufsize) )
     {
         printk(KERN_ERR "microcode: Bad data in microcode data file\n");
         return -EINVAL;
-- 
1.7.10.4