Use saturating_sub to prevent underflow

josephlr · josephlr · commit c1d539a35b30 · 2022-03-28T12:29:36.000-07:00
Signed-off-by: Joe Richey &lt;joerichey@google.com&gt;
diff --git a/src/structures/gdt.rs b/src/structures/gdt.rs
@@ -101,13 +101,13 @@ impl GlobalDescriptorTable {
     pub fn add_entry(&mut self, entry: Descriptor) -> SegmentSelector {
         let index = match entry {
             Descriptor::UserSegment(value) => {
-                if self.len > self.table.len() - 1 {
+                if self.len > self.table.len().saturating_sub(1) {
                     panic!("GDT full")
                 }
                 self.push(value)
             }
             Descriptor::SystemSegment(value_low, value_high) => {
-                if self.len > self.table.len() - 2 {
+                if self.len > self.table.len().saturating_sub(2) {
                     panic!("GDT requires two free spaces to hold a SystemSegment")
                 }
                 let index = self.push(value_low);

Original file line number	Diff line number	Diff line change
`@@ -101,13 +101,13 @@ impl GlobalDescriptorTable {`
`101`	`101`	`pub fn add_entry(&mut self, entry: Descriptor) -> SegmentSelector {`
`102`	`102`	`let index = match entry {`
`103`	`103`	`Descriptor::UserSegment(value) => {`
`104`		`- if self.len > self.table.len() - 1 {`
	`104`	`+ if self.len > self.table.len().saturating_sub(1) {`
`105`	`105`	`panic!("GDT full")`
`106`	`106`	`}`
`107`	`107`	`self.push(value)`
`108`	`108`	`}`
`109`	`109`	`Descriptor::SystemSegment(value_low, value_high) => {`
`110`		`- if self.len > self.table.len() - 2 {`
	`110`	`+ if self.len > self.table.len().saturating_sub(2) {`
`111`	`111`	`panic!("GDT requires two free spaces to hold a SystemSegment")`
`112`	`112`	`}`
`113`	`113`	`let index = self.push(value_low);`