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    Subject[PATCH 4.14 59/69] arm64: backtrace: Dont bother trying to unwind the userspace stack
    Date
    From: Will Deacon <will.deacon@arm.com>

    commit 1e6f5440a6814d28c32d347f338bfef68bc3e69d upstream.

    Calling dump_backtrace() with a pt_regs argument corresponding to
    userspace doesn't make any sense and our unwinder will simply print
    "Call trace:" before unwinding the stack looking for user frames.

    Rather than go through this song and dance, just return early if we're
    passed a user register state.

    Cc: <stable@vger.kernel.org>
    Fixes: 1149aad10b1e ("arm64: Add dump_backtrace() in show_regs")
    Reported-by: Kefeng Wang <wangkefeng.wang@huawei.com>
    Signed-off-by: Will Deacon <will.deacon@arm.com>
    Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

    ---
    arch/arm64/kernel/traps.c | 15 +++++++++------
    1 file changed, 9 insertions(+), 6 deletions(-)

    --- a/arch/arm64/kernel/traps.c
    +++ b/arch/arm64/kernel/traps.c
    @@ -145,10 +145,16 @@ static void dump_instr(const char *lvl,
    void dump_backtrace(struct pt_regs *regs, struct task_struct *tsk)
    {
    struct stackframe frame;
    - int skip;
    + int skip = 0;

    pr_debug("%s(regs = %p tsk = %p)\n", __func__, regs, tsk);

    + if (regs) {
    + if (user_mode(regs))
    + return;
    + skip = 1;
    + }
    +
    if (!tsk)
    tsk = current;

    @@ -169,7 +175,6 @@ void dump_backtrace(struct pt_regs *regs
    frame.graph = tsk->curr_ret_stack;
    #endif

    - skip = !!regs;
    printk("Call trace:\n");
    while (1) {
    unsigned long stack;
    @@ -232,15 +237,13 @@ static int __die(const char *str, int er
    return ret;

    print_modules();
    - __show_regs(regs);
    pr_emerg("Process %.*s (pid: %d, stack limit = 0x%p)\n",
    TASK_COMM_LEN, tsk->comm, task_pid_nr(tsk),
    end_of_stack(tsk));
    + show_regs(regs);

    - if (!user_mode(regs)) {
    - dump_backtrace(regs, tsk);
    + if (!user_mode(regs))
    dump_instr(KERN_EMERG, regs);
    - }

    return ret;
    }

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