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    Subject[PATCH 5.15 432/917] x86: Fix get_wchan() to support the ORC unwinder
    Date
    From: Qi Zheng <zhengqi.arch@bytedance.com>

    [ Upstream commit bc9bbb81730ea667c31c5b284f95ee312bab466f ]

    Currently, the kernel CONFIG_UNWINDER_ORC option is enabled by default
    on x86, but the implementation of get_wchan() is still based on the frame
    pointer unwinder, so the /proc/<pid>/wchan usually returned 0 regardless
    of whether the task <pid> is running.

    Reimplement get_wchan() by calling stack_trace_save_tsk(), which is
    adapted to the ORC and frame pointer unwinders.

    Fixes: ee9f8fce9964 ("x86/unwind: Add the ORC unwinder")
    Signed-off-by: Qi Zheng <zhengqi.arch@bytedance.com>
    Signed-off-by: Kees Cook <keescook@chromium.org>
    Signed-off-by: Peter Zijlstra (Intel) <peterz@infradead.org>
    Link: https://lkml.kernel.org/r/20211008111626.271115116@infradead.org
    Signed-off-by: Sasha Levin <sashal@kernel.org>
    ---
    arch/x86/kernel/process.c | 51 +++------------------------------------
    1 file changed, 3 insertions(+), 48 deletions(-)

    diff --git a/arch/x86/kernel/process.c b/arch/x86/kernel/process.c
    index f2f733bcb2b95..cd426c3283ee1 100644
    --- a/arch/x86/kernel/process.c
    +++ b/arch/x86/kernel/process.c
    @@ -945,58 +945,13 @@ unsigned long arch_randomize_brk(struct mm_struct *mm)
    */
    unsigned long get_wchan(struct task_struct *p)
    {
    - unsigned long start, bottom, top, sp, fp, ip, ret = 0;
    - int count = 0;
    + unsigned long entry = 0;

    if (p == current || task_is_running(p))
    return 0;

    - if (!try_get_task_stack(p))
    - return 0;
    -
    - start = (unsigned long)task_stack_page(p);
    - if (!start)
    - goto out;
    -
    - /*
    - * Layout of the stack page:
    - *
    - * ----------- topmax = start + THREAD_SIZE - sizeof(unsigned long)
    - * PADDING
    - * ----------- top = topmax - TOP_OF_KERNEL_STACK_PADDING
    - * stack
    - * ----------- bottom = start
    - *
    - * The tasks stack pointer points at the location where the
    - * framepointer is stored. The data on the stack is:
    - * ... IP FP ... IP FP
    - *
    - * We need to read FP and IP, so we need to adjust the upper
    - * bound by another unsigned long.
    - */
    - top = start + THREAD_SIZE - TOP_OF_KERNEL_STACK_PADDING;
    - top -= 2 * sizeof(unsigned long);
    - bottom = start;
    -
    - sp = READ_ONCE(p->thread.sp);
    - if (sp < bottom || sp > top)
    - goto out;
    -
    - fp = READ_ONCE_NOCHECK(((struct inactive_task_frame *)sp)->bp);
    - do {
    - if (fp < bottom || fp > top)
    - goto out;
    - ip = READ_ONCE_NOCHECK(*(unsigned long *)(fp + sizeof(unsigned long)));
    - if (!in_sched_functions(ip)) {
    - ret = ip;
    - goto out;
    - }
    - fp = READ_ONCE_NOCHECK(*(unsigned long *)fp);
    - } while (count++ < 16 && !task_is_running(p));
    -
    -out:
    - put_task_stack(p);
    - return ret;
    + stack_trace_save_tsk(p, &entry, 1, 0);
    + return entry;
    }

    long do_arch_prctl_common(struct task_struct *task, int option,
    --
    2.33.0


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