From: Thomas Gleixner tglx@linutronix.de
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@linutronix.de Signed-off-by: Peter Zijlstra (Intel) peterz@infradead.org Cc: stable@kernel.org Signed-off-by: Greg Kroah-Hartman gregkh@linuxfoundation.org
--- 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;
/*