x86/microcode/intel: Handle truncated microcode images more robustly

We do not check the input data bounds containing the microcode before
copying a struct microcode_intel_header from it. A specially crafted
microcode could cause the kernel to read invalid memory and lead to a
denial-of-service.

Signed-off-by: Quentin Casasnovas <quentin.casasnovas@oracle.com>
Cc: "H. Peter Anvin" <hpa@zytor.com>
Cc: Fenghua Yu <fenghua.yu@intel.com>
Link: http://lkml.kernel.org/r/1422964824-22056-3-git-send-email-quentin.casasnovas@oracle.com
[ Made error message differ from the next one and flipped comparison. ]
Signed-off-by: Borislav Petkov <bp@suse.de>

arch/x86/kernel/cpu/microcode/intel.c

@@ -196,6 +196,11 @@ static enum ucode_state generic_load_microcode(int cpu, void *data, size_t size,
 		struct microcode_header_intel mc_header;
 		unsigned int mc_size;
 
+		if (leftover < sizeof(mc_header)) {
+			pr_err("error! Truncated header in microcode data file\n");
+			break;
+		}
+
 		if (get_ucode_data(&mc_header, ucode_ptr, sizeof(mc_header)))
 			break;
 

arch/x86/kernel/cpu/microcode/intel_early.c

@@ -322,6 +322,10 @@ get_matching_model_microcode(int cpu, unsigned long start,
 	int i;
 
 	while (leftover && mc_saved_count < ARRAY_SIZE(mc_saved_tmp)) {
+
+		if (leftover < sizeof(mc_header))
+			break;
+
 		mc_header = (struct microcode_header_intel *)ucode_ptr;
 
 		mc_size = get_totalsize(mc_header);