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    Subject[tip:x86/debug] x86: Add stack top margin for stack overflow checking
    Commit-ID:  d2db6610219cbcadceea6c43ee03d89068b7d759
    Gitweb: http://git.kernel.org/tip/d2db6610219cbcadceea6c43ee03d89068b7d759
    Author: Mitsuo Hayasaka <mitsuo.hayasaka.hu@hitachi.com>
    AuthorDate: Wed, 7 Dec 2011 17:29:10 +0900
    Committer: Ingo Molnar <mingo@elte.hu>
    CommitDate: Wed, 7 Dec 2011 09:27:11 +0100

    x86: Add stack top margin for stack overflow checking

    It seems that a margin for stack overflow checking is added to
    top of a kernel stack but is not added to IRQ and exception
    stacks in stack_overflow_check(). Therefore, the overflows of
    IRQ and exception stacks are always detected only after they
    actually occurred and data corruption might occur due to them.

    This patch adds the margin to top of IRQ and exception stacks
    as well as a kernel stack to enhance reliability.

    Signed-off-by: Mitsuo Hayasaka <mitsuo.hayasaka.hu@hitachi.com>
    Cc: yrl.pp-manager.tt@hitachi.com
    Cc: Linus Torvalds <torvalds@linux-foundation.org>
    Cc: Andrew Morton <akpm@linux-foundation.org>
    Link: http://lkml.kernel.org/r/20111207082910.9847.3359.stgit@ltc219.sdl.hitachi.co.jp
    [ removed the #undef - we typically don't do that for uncommon names ]
    Signed-off-by: Ingo Molnar <mingo@elte.hu>
    ---
    arch/x86/kernel/irq_64.c | 8 +++++---
    1 files changed, 5 insertions(+), 3 deletions(-)

    diff --git a/arch/x86/kernel/irq_64.c b/arch/x86/kernel/irq_64.c
    index 54e2b2b..d04d3ec 100644
    --- a/arch/x86/kernel/irq_64.c
    +++ b/arch/x86/kernel/irq_64.c
    @@ -38,6 +38,7 @@ int sysctl_panic_on_stackoverflow;
    static inline void stack_overflow_check(struct pt_regs *regs)
    {
    #ifdef CONFIG_DEBUG_STACKOVERFLOW
    +#define STACK_TOP_MARGIN 128
    struct orig_ist *oist;
    u64 irq_stack_top, irq_stack_bottom;
    u64 estack_top, estack_bottom;
    @@ -47,17 +48,18 @@ static inline void stack_overflow_check(struct pt_regs *regs)
    return;

    if (regs->sp >= curbase + sizeof(struct thread_info) +
    - sizeof(struct pt_regs) + 128 &&
    + sizeof(struct pt_regs) + STACK_TOP_MARGIN &&
    regs->sp <= curbase + THREAD_SIZE)
    return;

    - irq_stack_top = (u64)__get_cpu_var(irq_stack_union.irq_stack);
    + irq_stack_top = (u64)__get_cpu_var(irq_stack_union.irq_stack) +
    + STACK_TOP_MARGIN;
    irq_stack_bottom = (u64)__get_cpu_var(irq_stack_ptr);
    if (regs->sp >= irq_stack_top && regs->sp <= irq_stack_bottom)
    return;

    oist = &__get_cpu_var(orig_ist);
    - estack_top = (u64)oist->ist[0] - EXCEPTION_STKSZ;
    + estack_top = (u64)oist->ist[0] - EXCEPTION_STKSZ + STACK_TOP_MARGIN;
    estack_bottom = (u64)oist->ist[N_EXCEPTION_STACKS - 1];
    if (regs->sp >= estack_top && regs->sp <= estack_bottom)
    return;

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