From 880a98c339961eaa074393e3a2117cbe9125b8bb Mon Sep 17 00:00:00 2001 From: Thomas Gleixner Date: Thu, 21 Nov 2019 00:40:24 +0100 Subject: [PATCH] x86/cpu_entry_area: Add guard page for entry stack on 32bit 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 Signed-off-by: Peter Zijlstra (Intel) Cc: stable@kernel.org --- arch/x86/include/asm/cpu_entry_area.h | 6 +++++- 1 file changed, 5 insertions(+), 1 deletion(-) diff --git a/arch/x86/include/asm/cpu_entry_area.h b/arch/x86/include/asm/cpu_entry_area.h index 8348f7d..905d89c 100644 --- 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; /* -- 2.7.4