From: Thomas Gleixner <tglx@xxxxxxxxxxxxx>
commit 880a98c339961eaa074393e3a2117cbe9125b8bb upstream.
The entry stack in the cpu entry area is protected against overflow by the
readonly GDT on 64-bit, but on 32-bit the GDT needs to be writeable and
therefore does not trigger a fault on stack overflow.
Add a guard page.
Fixes: c482feefe1ae ("x86/entry/64: Make cpu_entry_area.tss read-only")
Signed-off-by: Thomas Gleixner <tglx@xxxxxxxxxxxxx>
Signed-off-by: Peter Zijlstra (Intel) <peterz@xxxxxxxxxxxxx>
Cc: stable@xxxxxxxxxx
Signed-off-by: Greg Kroah-Hartman <gregkh@xxxxxxxxxxxxxxxxxxx>
---
arch/x86/include/asm/cpu_entry_area.h | 6 +++++-
1 file changed, 5 insertions(+), 1 deletion(-)
--- a/arch/x86/include/asm/cpu_entry_area.h
+++ b/arch/x86/include/asm/cpu_entry_area.h
@@ -78,8 +78,12 @@ struct cpu_entry_area {
/*
* The GDT is just below entry_stack and thus serves (on x86_64) as
- * a a read-only guard page.
+ * a read-only guard page. On 32-bit the GDT must be writeable, so
+ * it needs an extra guard page.
*/
+#ifdef CONFIG_X86_32
+ char guard_entry_stack[PAGE_SIZE];
+#endif
struct entry_stack_page entry_stack_page;
/*
