[PATCH -v2 4/4] x86: cleanup the range of stack overflow checking

[Mitsuo Hayasaka]

The overflow checking of kernel stack checks if the stack pointer
points to the available kernel stack range, which is derived from
the original overflow checking.

It is clear that curbase address is always less than low boundary of
available kernel stack. So, this patch removes the first condition
that checks if the pointer is higher than curbase.

Signed-off-by: Mitsuo Hayasaka <mitsuo.hayasaka.hu@xxxxxxxxxxx>
Cc: Thomas Gleixner <tglx@xxxxxxxxxxxxx>
Cc: Ingo Molnar <mingo@xxxxxxxxxx>
Cc: "H. Peter Anvin" <hpa@xxxxxxxxx>
---

 arch/x86/kernel/irq_64.c |    7 +++----
 1 files changed, 3 insertions(+), 4 deletions(-)

diff --git a/arch/x86/kernel/irq_64.c b/arch/x86/kernel/irq_64.c
index 5448bf6..c8c9a78 100644
--- a/arch/x86/kernel/irq_64.c
+++ b/arch/x86/kernel/irq_64.c
@@ -46,10 +46,9 @@ static inline void stack_overflow_check(struct pt_regs *regs)
 	if (user_mode_vm(regs))
 		return;
 
-	if (regs->sp >= curbase &&
-	    regs->sp <= curbase + THREAD_SIZE &&
-	    regs->sp >= curbase + sizeof(struct thread_info) +
-				  sizeof(struct pt_regs) + 128)
+	if (regs->sp >= curbase + sizeof(struct thread_info) +
+				  sizeof(struct pt_regs) + 128 &&
+	    regs->sp <= curbase + THREAD_SIZE)
 		return;
 
 	irq_stack_top = (u64)__get_cpu_var(irq_stack_union.irq_stack);

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