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    SubjectRe: [RFC PATCH 1/5] x86: add user_mode_vm check in stack_overflow_check
    On Mon, Nov 07, 2011 at 02:52:35PM +0900, Mitsuo Hayasaka wrote:
    > 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.

    I think you mean to say 'points'.

    How do we accidently point the stack pointer to the kernel stack?

    >
    > 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@hitachi.com>
    > Cc: Thomas Gleixner <tglx@linutronix.de>
    > Cc: Ingo Molnar <mingo@redhat.com>
    > Cc: "H. Peter Anvin" <hpa@zytor.com>
    > ---
    >
    > 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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