[PATCH] x86: Increase exception stack sizes

[Peter Zijlstra]

On Wed, Sep 15, 2021 at 03:34:20PM +0800, 王贇 wrote:
> Hi, Dave, Peter
> 
> What if we just increase the stack size when ftrace enabled?

I think we can do an unconditional increase. But please first test that
guard page patch :-)

---
Subject: x86: Increase exception stack sizes
From: Peter Zijlstra <peterz@xxxxxxxxxxxxx>
Date: Wed Sep 15 16:19:46 CEST 2021

It turns out that a single page of stack is trivial to overflow with
all the tracing gunk enabled. Raise the exception stacks to 2 pages,
which is still half the interrupt stacks, which are at 4 pages.

Reported-by: Michael Wang <yun.wang@xxxxxxxxxxxxxxxxx>
Signed-off-by: Peter Zijlstra (Intel) <peterz@xxxxxxxxxxxxx>
---
 arch/x86/include/asm/page_64_types.h |    2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

--- a/arch/x86/include/asm/page_64_types.h
+++ b/arch/x86/include/asm/page_64_types.h
@@ -15,7 +15,7 @@
 #define THREAD_SIZE_ORDER	(2 + KASAN_STACK_ORDER)
 #define THREAD_SIZE  (PAGE_SIZE << THREAD_SIZE_ORDER)
 
-#define EXCEPTION_STACK_ORDER (0 + KASAN_STACK_ORDER)
+#define EXCEPTION_STACK_ORDER (1 + KASAN_STACK_ORDER)
 #define EXCEPTION_STKSZ (PAGE_SIZE << EXCEPTION_STACK_ORDER)
 
 #define IRQ_STACK_ORDER (2 + KASAN_STACK_ORDER)