[RFC PATCH 1/5] x86: add user_mode_vm check in stack_overflow_check

[Mitsuo Hayasaka]

The kernel stack overflow is checked in stack_overflow_check(),
which may wrongly detect the overflow if the stack pointer
pointed to the kernel stack accidentally.

This patch adds user-mode-vm checking before it to avoid this
misdetection and bails out early if the user stack is used.

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 |    3 +++
 1 files changed, 3 insertions(+), 0 deletions(-)

diff --git a/arch/x86/kernel/irq_64.c b/arch/x86/kernel/irq_64.c
index acf8fbf..69bca46 100644
--- a/arch/x86/kernel/irq_64.c
+++ b/arch/x86/kernel/irq_64.c
@@ -38,6 +38,9 @@ static inline void stack_overflow_check(struct pt_regs *regs)
 #ifdef CONFIG_DEBUG_STACKOVERFLOW
 	u64 curbase = (u64)task_stack_page(current);
 
+	if (user_mode_vm(regs))
+		return;
+
 	WARN_ONCE(regs->sp >= curbase &&
 		  regs->sp <= curbase + THREAD_SIZE &&
 		  regs->sp <  curbase + sizeof(struct thread_info) +

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