[PATCH v2] x86/microcode: Change checksum to u32

[Chris Bainbridge]

Checksum should be unsigned 32-bit otherwise the calculation overflow
results in undefined behaviour:

[    0.000000] ================================================================================
[    0.000000] UBSAN: Undefined behaviour in arch/x86/kernel/cpu/microcode/intel_lib.c:105:12
[    0.000000] signed integer overflow:
[    0.000000] -1500151068 + -2125470173 cannot be represented in type 'int'
[    0.000000] CPU: 0 PID: 0 Comm: swapper Not tainted 4.5.0-rc5+ #495
[    0.000000]  0000000000000086 0000000000000086 0000000000000000 ffffffff83203968
[    0.000000]  ffffffff81b30952 ffffffff834c43b8 ffffffff83203998 ffffffff814fe623
[    0.000000]  ffffffff83203980 ffffffff81bcdf2d ffffffff8339a448 ffffffff83203a08
[    0.000000] Call Trace:
[    0.000000]  [<ffffffff81b30952>] dump_stack+0x4e/0x6c
[    0.000000]  [<ffffffff814fe623>] ? inotify_ioctl+0x43/0x1c0
[    0.000000]  [<ffffffff81bcdf2d>] ubsan_epilogue+0xd/0x40
[    0.000000]  [<ffffffff81bce2fd>] handle_overflow+0xbd/0xe0
[    0.000000]  [<ffffffff81bce32e>] __ubsan_handle_add_overflow+0xe/0x10
[    0.000000]  [<ffffffff81148e45>] microcode_sanity_check+0x405/0x590
[    0.000000]  [<ffffffff8549b01b>] get_matching_model_microcode.isra.2.constprop.8+0xa5/0x345
[    0.000000]  [<ffffffff8548615d>] ? early_idt_handler_common+0x3d/0xae
[    0.000000]  [<ffffffff81b50962>] ? strlcpy+0x52/0xa0
[    0.000000]  [<ffffffff81b30ce1>] ? find_cpio_data+0x371/0x510
[    0.000000]  [<ffffffff8549b461>] load_ucode_intel_bsp+0xa1/0xe5
[    0.000000]  [<ffffffff8549aea8>] load_ucode_bsp+0xdf/0xf3
[    0.000000]  [<ffffffff8549aea8>] ? load_ucode_bsp+0xdf/0xf3
[    0.000000]  [<ffffffff8548671c>] x86_64_start_kernel+0xd1/0xee
[    0.000000] ================================================================================

Link: https://lkml.org/lkml/2016/2/27/79
Signed-off-by: Chris Bainbridge <chris.bainbridge@xxxxxxxxx>
---
 arch/x86/kernel/cpu/microcode/intel_lib.c | 8 ++++----
 1 file changed, 4 insertions(+), 4 deletions(-)

diff --git a/arch/x86/kernel/cpu/microcode/intel_lib.c b/arch/x86/kernel/cpu/microcode/intel_lib.c
index b96896bcbdaf..99ca2c935777 100644
--- a/arch/x86/kernel/cpu/microcode/intel_lib.c
+++ b/arch/x86/kernel/cpu/microcode/intel_lib.c
@@ -49,7 +49,7 @@ int microcode_sanity_check(void *mc, int print_err)
 	unsigned long total_size, data_size, ext_table_size;
 	struct microcode_header_intel *mc_header = mc;
 	struct extended_sigtable *ext_header = NULL;
-	int sum, orig_sum, ext_sigcount = 0, i;
+	u32 sum, orig_sum, ext_sigcount = 0, i;
 	struct extended_signature *ext_sig;
 
 	total_size = get_totalsize(mc_header);
@@ -85,8 +85,8 @@ int microcode_sanity_check(void *mc, int print_err)
 
 	/* check extended table checksum */
 	if (ext_table_size) {
-		int ext_table_sum = 0;
-		int *ext_tablep = (int *)ext_header;
+		u32 ext_table_sum = 0;
+		u32 *ext_tablep = (u32 *)ext_header;
 
 		i = ext_table_size / DWSIZE;
 		while (i--)
@@ -102,7 +102,7 @@ int microcode_sanity_check(void *mc, int print_err)
 	orig_sum = 0;
 	i = (MC_HEADER_SIZE + data_size) / DWSIZE;
 	while (i--)
-		orig_sum += ((int *)mc)[i];
+		orig_sum += ((u32 *)mc)[i];
 	if (orig_sum) {
 		if (print_err)
 			pr_err("aborting, bad checksum\n");
-- 
2.1.4