#include <linux/sched.h>
#include <asm/ptrace.h>
#include <asm/bitops.h>
#include <asm/stacktrace.h>
#include <asm/unwind.h>

#define FRAME_HEADER_SIZE (sizeof(long) * 2)

/*
 * This disables KASAN checking when reading a value from another task's stack,
 * since the other task could be running on another CPU and could have poisoned
 * the stack in the meantime.
 */
#define READ_ONCE_TASK_STACK(task, x)                   \
({                                                      \
        unsigned long val;                              \
        if (task == current)                            \
                val = READ_ONCE(x);                     \
        else                                            \
                val = READ_ONCE_NOCHECK(x);             \
        val;                                            \
})

static void unwind_dump(struct unwind_state *state, unsigned long *sp)
{
        static bool dumped_before = false;
        bool prev_zero, zero = false;
        unsigned long word;

        if (dumped_before)
                return;

        dumped_before = true;

        printk_deferred("unwind stack type:%d next_sp:%p mask:%lx graph_idx:%d\n",
                        state->stack_info.type, state->stack_info.next_sp,
                        state->stack_mask, state->graph_idx);

        for (sp = state->orig_sp; sp < state->stack_info.end; sp++) {
                word = READ_ONCE_NOCHECK(*sp);

                prev_zero = zero;
                zero = word == 0;

                if (zero) {
                        if (!prev_zero)
                                printk_deferred("%p: %016x ...\n", sp, 0);
                        continue;
                }

                printk_deferred("%p: %016lx (%pB)\n", sp, word, (void *)word);
        }
}

unsigned long unwind_get_return_address(struct unwind_state *state)
{
        unsigned long addr;
        unsigned long *addr_p = unwind_get_return_address_ptr(state);

        if (unwind_done(state))
                return 0;

        if (state->regs && user_mode(state->regs))
                return 0;

        addr = READ_ONCE_TASK_STACK(state->task, *addr_p);
        addr = ftrace_graph_ret_addr(state->task, &state->graph_idx, addr,
                                     addr_p);

        return __kernel_text_address(addr) ? addr : 0;
}
EXPORT_SYMBOL_GPL(unwind_get_return_address);

static size_t regs_size(struct pt_regs *regs)
{
        /* x86_32 regs from kernel mode are two words shorter: */
        if (IS_ENABLED(CONFIG_X86_32) && !user_mode(regs))
                return sizeof(*regs) - 2*sizeof(long);

        return sizeof(*regs);
}

static bool is_last_task_frame(struct unwind_state *state)
{
        unsigned long bp = (unsigned long)state->bp;
        unsigned long regs = (unsigned long)task_pt_regs(state->task);

        /*
         * We have to check for the last task frame at two different locations
         * because gcc can occasionally decide to realign the stack pointer and
         * change the offset of the stack frame by a word in the prologue of a
         * function called by head/entry code.
         */
        return bp == regs - FRAME_HEADER_SIZE ||
               bp == regs - FRAME_HEADER_SIZE - sizeof(long);
}

/*
 * This determines if the frame pointer actually contains an encoded pointer to
 * pt_regs on the stack.  See ENCODE_FRAME_POINTER.
 */
static struct pt_regs *decode_frame_pointer(unsigned long *bp)
{
        unsigned long regs = (unsigned long)bp;

        if (!(regs & 0x1))
                return NULL;

        return (struct pt_regs *)(regs & ~0x1);
}

static bool update_stack_state(struct unwind_state *state, void *addr,
                               size_t len)
{
        struct stack_info *info = &state->stack_info;
        enum stack_type orig_type = info->type;

        /*
         * If addr isn't on the current stack, switch to the next one.
         *
         * We may have to traverse multiple stacks to deal with the possibility
         * that 'info->next_sp' could point to an empty stack and 'addr' could
         * be on a subsequent stack.
         */
        while (!on_stack(info, addr, len))
                if (get_stack_info(info->next_sp, state->task, info,
                                   &state->stack_mask))
                        return false;

        if (!state->orig_sp || info->type != orig_type)
                state->orig_sp = addr;

        return true;
}

bool unwind_next_frame(struct unwind_state *state)
{
        struct pt_regs *regs;
        unsigned long *next_bp, *next_frame;
        size_t next_len;
        enum stack_type prev_type = state->stack_info.type;

        if (unwind_done(state))
                return false;

        /* have we reached the end? */
        if (state->regs && user_mode(state->regs))
                goto the_end;

        if (is_last_task_frame(state)) {
                regs = task_pt_regs(state->task);

                /*
                 * kthreads (other than the boot CPU's idle thread) have some
                 * partial regs at the end of their stack which were placed
                 * there by copy_thread_tls().  But the regs don't have any
                 * useful information, so we can skip them.
                 *
                 * This user_mode() check is slightly broader than a PF_KTHREAD
                 * check because it also catches the awkward situation where a
                 * newly forked kthread transitions into a user task by calling
                 * do_execve(), which eventually clears PF_KTHREAD.
                 */
                if (!user_mode(regs))
                        goto the_end;

                /*
                 * We're almost at the end, but not quite: there's still the
                 * syscall regs frame.  Entry code doesn't encode the regs
                 * pointer for syscalls, so we have to set it manually.
                 */
                state->regs = regs;
                state->bp = NULL;
                return true;
        }

        /* get the next frame pointer */
        if (state->regs)
                next_bp = (unsigned long *)state->regs->bp;
        else
                next_bp = (unsigned long *)READ_ONCE_TASK_STACK(state->task,*state->bp);

        /* is the next frame pointer an encoded pointer to pt_regs? */
        regs = decode_frame_pointer(next_bp);
        if (regs) {
                next_frame = (unsigned long *)regs;
                next_len = sizeof(*regs);
        } else {
                next_frame = next_bp;
                next_len = FRAME_HEADER_SIZE;
        }

        /* make sure the next frame's data is accessible */
        if (!update_stack_state(state, next_frame, next_len)) {
                /*
                 * Don't warn on bad regs->bp.  An interrupt in entry code
                 * might cause a false positive warning.
                 */
                if (state->regs)
                        goto the_end;

                goto bad_address;
        }

        /* Make sure it only unwinds up and doesn't overlap the last frame: */
        if (state->stack_info.type == prev_type) {
                if (state->regs && (void *)next_frame < (void *)state->regs + regs_size(state->regs))
                        goto bad_address;

                if (state->bp && (void *)next_frame < (void *)state->bp + FRAME_HEADER_SIZE)
                        goto bad_address;
        }

        /* move to the next frame */
        if (regs) {
                state->regs = regs;
                state->bp = NULL;
        } else {
                state->bp = next_bp;
                state->regs = NULL;
        }

        return true;

bad_address:
        /*
         * When unwinding a non-current task, the task might actually be
         * running on another CPU, in which case it could be modifying its
         * stack while we're reading it.  This is generally not a problem and
         * can be ignored as long as the caller understands that unwinding
         * another task will not always succeed.
         */
        if (state->task != current)
                goto the_end;

        if (state->regs) {
                printk_deferred_once(KERN_WARNING
                        "WARNING: kernel stack regs at %p in %s:%d has bad 'bp' value %p\n",
                        state->regs, state->task->comm,
                        state->task->pid, next_frame);
                unwind_dump(state, (unsigned long *)state->regs);
        } else {
                printk_deferred_once(KERN_WARNING
                        "WARNING: kernel stack frame pointer at %p in %s:%d has bad value %p\n",
                        state->bp, state->task->comm,
                        state->task->pid, next_frame);
                unwind_dump(state, state->bp);
        }
the_end:
        state->stack_info.type = STACK_TYPE_UNKNOWN;
        return false;
}
EXPORT_SYMBOL_GPL(unwind_next_frame);

void __unwind_start(struct unwind_state *state, struct task_struct *task,
                    struct pt_regs *regs, unsigned long *first_frame)
{
        unsigned long *bp, *frame;
        size_t len;

        memset(state, 0, sizeof(*state));
        state->task = task;

        /* don't even attempt to start from user mode regs */
        if (regs && user_mode(regs)) {
                state->stack_info.type = STACK_TYPE_UNKNOWN;
                return;
        }

        /* set up the starting stack frame */
        bp = get_frame_pointer(task, regs);
        regs = decode_frame_pointer(bp);
        if (regs) {
                state->regs = regs;
                frame = (unsigned long *)regs;
                len = sizeof(*regs);
        } else {
                state->bp = bp;
                frame = bp;
                len = FRAME_HEADER_SIZE;
        }

        /* initialize stack info and make sure the frame data is accessible */
        get_stack_info(frame, state->task, &state->stack_info,
                       &state->stack_mask);
        update_stack_state(state, frame, len);

        /*
         * The caller can provide the address of the first frame directly
         * (first_frame) or indirectly (regs->sp) to indicate which stack frame
         * to start unwinding at.  Skip ahead until we reach it.
         */
        while (!unwind_done(state) &&
               (!on_stack(&state->stack_info, first_frame, sizeof(long)) ||
                        state->bp < first_frame))
                unwind_next_frame(state);
}
EXPORT_SYMBOL_GPL(__unwind_start);