Change in flashrom[master]: ich_descriptors.c: Ensure unsigned types >=0 on to prevent underflow

[Anastasia Klimchuk (Code Review)]

Anastasia Klimchuk has submitted this change. ( https://review.coreboot.org/c/flashrom/+/62764 )

Change subject: ich_descriptors.c: Ensure unsigned types >=0 on to prevent underflow
......................................................................

ich_descriptors.c: Ensure unsigned types >=0 on to prevent underflow

Unsigned types show undefined behaviour if they are subtracted by a
value greater than their own (mostly it wraps to the max value). Using
this value for left shifting could be even more dangerous.

Change-Id: I5921cc571f3dca5188ca1973dba6ececbcbe2f39
Signed-off-by: Aarya Chaumal 
Reviewed-on: https://review.coreboot.org/c/flashrom/+/62764
Tested-by: build bot (Jenkins) 
Reviewed-by: Anastasia Klimchuk 
---
M ich_descriptors.c
1 file changed, 5 insertions(+), 4 deletions(-)

Approvals:
  build bot (Jenkins): Verified
  Anastasia Klimchuk: Looks good to me, approved

diff --git a/ich_descriptors.c b/ich_descriptors.c
index 7c03499..4d85e08 100644
--- a/ich_descriptors.c
+++ b/ich_descriptors.c
@@ -502,16 +502,17 @@
    		msg_pdbg2(" RegA RegB RegC RegD RegE RegF\n");
    	}
    	for (i = 0; i < nm; i++) {
+			const unsigned int ext_region_start = 12;
    		size_t j;
    		msg_pdbg2("%-4s", master_names[i]);
-			for (j = 0; j < (size_t)min(num_regions, 12); j++)
+			for (j = 0; j < (size_t)min(num_regions, ext_region_start); j++)
    			msg_pdbg2("  %c%c ",
    				  desc->master.mstr[i].read & (1 << j) ? 'r' : ' ',
    				  desc->master.mstr[i].write & (1 << j) ? 'w' : ' ');
-			for (; j < num_regions; j++)
+			for (j = ext_region_start; j < num_regions; j++)
    			msg_pdbg2("  %c%c ",
-					  desc->master.mstr[i].ext_read & (1 << (j - 12)) ? 'r' : ' ',
-					  desc->master.mstr[i].ext_write & (1 << (j - 12)) ? 'w' : ' ');
+					  desc->master.mstr[i].ext_read & (1 << (j - ext_region_start)) ? 'r' : ' ',
+					  desc->master.mstr[i].ext_write & (1 << (j - ext_region_start)) ? 'w' : ' ');
    		msg_pdbg2("\n");
    	}
    } else if (cs == CHIPSET_C620_SERIES_LEWISBURG) {