[Xen-devel] [PATCH 3/3] x86/microcode: Avoid undefined behaviour from signed integer overflow

[Andrew Cooper <andrew.cooper3@xxxxxxxxxx>]

The checksum should be calculated using unsigned 32bit integers, as it is
intended to overflow and end at 0.

Signed-off-by: Andrew Cooper <andrew.cooper3@xxxxxxxxxx>
---
CC: Jan Beulich <JBeulich@xxxxxxxx>
CC: Kevin Tian <kevin.tian@xxxxxxxxx>
CC: Jun Nakajima <jun.nakajima@xxxxxxxxx>
---
 xen/arch/x86/microcode_intel.c | 5 +++--
 1 file changed, 3 insertions(+), 2 deletions(-)

diff --git a/xen/arch/x86/microcode_intel.c b/xen/arch/x86/microcode_intel.c
index 6949c25..5b411b4 100644
--- a/xen/arch/x86/microcode_intel.c
+++ b/xen/arch/x86/microcode_intel.c
@@ -143,7 +143,8 @@ static int microcode_sanity_check(void *mc)
     struct extended_sigtable *ext_header = NULL;
     struct extended_signature *ext_sig;
     unsigned long total_size, data_size, ext_table_size;
-    int sum, orig_sum, ext_sigcount = 0, i;
+    uint32_t sum, orig_sum;
+    int ext_sigcount = 0, i;
 
     total_size = get_totalsize(mc_header);
     data_size = get_datasize(mc_header);
@@ -201,7 +202,7 @@ static int microcode_sanity_check(void *mc)
     orig_sum = 0;
     i = (MC_HEADER_SIZE + data_size) / DWSIZE;
     while ( i-- )
-        orig_sum += ((int *)mc)[i];
+        orig_sum += ((uint32_t *)mc)[i];
     if ( orig_sum )
     {
         printk(KERN_ERR "microcode: aborting, bad checksum\n");
-- 
2.1.4


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