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    Subject[PATCH 5.1 180/405] x86/irq/64: Limit IST stack overflow check to #DB stack
    Date
    [ Upstream commit 7dbcf2b0b770eeb803a416ee8dcbef78e6389d40 ]

    Commit

    37fe6a42b343 ("x86: Check stack overflow in detail")

    added a broad check for the full exception stack area, i.e. it considers
    the full exception stack area as valid.

    That's wrong in two aspects:

    1) It does not check the individual areas one by one

    2) #DF, NMI and #MCE are not enabling interrupts which means that a
    regular device interrupt cannot happen in their context. In fact if a
    device interrupt hits one of those IST stacks that's a bug because some
    code path enabled interrupts while handling the exception.

    Limit the check to the #DB stack and consider all other IST stacks as
    'overflow' or invalid.

    Signed-off-by: Thomas Gleixner <tglx@linutronix.de>
    Signed-off-by: Borislav Petkov <bp@suse.de>
    Cc: Andy Lutomirski <luto@kernel.org>
    Cc: "H. Peter Anvin" <hpa@zytor.com>
    Cc: Ingo Molnar <mingo@redhat.com>
    Cc: Josh Poimboeuf <jpoimboe@redhat.com>
    Cc: Mitsuo Hayasaka <mitsuo.hayasaka.hu@hitachi.com>
    Cc: Nicolai Stange <nstange@suse.de>
    Cc: Sean Christopherson <sean.j.christopherson@intel.com>
    Cc: x86-ml <x86@kernel.org>
    Link: https://lkml.kernel.org/r/20190414160143.682135110@linutronix.de
    Signed-off-by: Sasha Levin <sashal@kernel.org>
    ---
    arch/x86/kernel/irq_64.c | 19 ++++++++++++++-----
    1 file changed, 14 insertions(+), 5 deletions(-)

    diff --git a/arch/x86/kernel/irq_64.c b/arch/x86/kernel/irq_64.c
    index 0469cd078db15..b50ac9c7397bb 100644
    --- a/arch/x86/kernel/irq_64.c
    +++ b/arch/x86/kernel/irq_64.c
    @@ -26,9 +26,18 @@ int sysctl_panic_on_stackoverflow;
    /*
    * Probabilistic stack overflow check:
    *
    - * Only check the stack in process context, because everything else
    - * runs on the big interrupt stacks. Checking reliably is too expensive,
    - * so we just check from interrupts.
    + * Regular device interrupts can enter on the following stacks:
    + *
    + * - User stack
    + *
    + * - Kernel task stack
    + *
    + * - Interrupt stack if a device driver reenables interrupts
    + * which should only happen in really old drivers.
    + *
    + * - Debug IST stack
    + *
    + * All other contexts are invalid.
    */
    static inline void stack_overflow_check(struct pt_regs *regs)
    {
    @@ -53,8 +62,8 @@ static inline void stack_overflow_check(struct pt_regs *regs)
    return;

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

    --
    2.20.1


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