Merge tag 'iio-for-4.13b' of git://git.kernel.org/pub/scm/linux/kernel/git/jic23...

[mirror_ubuntu-artful-kernel.git] / arch / x86 / kernel / unwind_frame.c

#include <linux/sched.h>
#include <linux/sched/task.h>
#include <linux/sched/task_stack.h>
#include <linux/interrupt.h>
#include <asm/sections.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)
{
        static bool dumped_before = false;
        bool prev_zero, zero = false;
        unsigned long word, *sp;
        struct stack_info stack_info = {0};
        unsigned long visit_mask = 0;

        if (dumped_before)
                return;

        dumped_before = true;

        printk_deferred("unwind stack type:%d next_sp:%p mask:0x%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; sp = PTR_ALIGN(stack_info.next_sp, sizeof(long))) {
                if (get_stack_info(sp, state->task, &stack_info, &visit_mask))
                        break;

                for (; sp < stack_info.end; sp++) {

                        word = READ_ONCE_NOCHECK(*sp);

                        prev_zero = zero;
                        zero = word == 0;

                        if (zero) {
                                if (!prev_zero)
                                        printk_deferred("%p: %0*x ...\n",
                                                        sp, BITS_PER_LONG/4, 0);
                                continue;
                        }

                        printk_deferred("%p: %0*lx (%pB)\n",
                                        sp, BITS_PER_LONG/4, word, (void *)word);
                }
        }
}

unsigned long unwind_get_return_address(struct unwind_state *state)
{
        if (unwind_done(state))
                return 0;

        return __kernel_text_address(state->ip) ? state->ip : 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 in_entry_code(unsigned long ip)
{
        char *addr = (char *)ip;

        if (addr >= __entry_text_start && addr < __entry_text_end)
                return true;

#if defined(CONFIG_FUNCTION_GRAPH_TRACER) || defined(CONFIG_KASAN)
        if (addr >= __irqentry_text_start && addr < __irqentry_text_end)
                return true;
#endif

        return false;
}

static inline unsigned long *last_frame(struct unwind_state *state)
{
        return (unsigned long *)task_pt_regs(state->task) - 2;
}

static bool is_last_frame(struct unwind_state *state)
{
        return state->bp == last_frame(state);
}

#ifdef CONFIG_X86_32
#define GCC_REALIGN_WORDS 3
#else
#define GCC_REALIGN_WORDS 1
#endif

static inline unsigned long *last_aligned_frame(struct unwind_state *state)
{
        return last_frame(state) - GCC_REALIGN_WORDS;
}

static bool is_last_aligned_frame(struct unwind_state *state)
{
        unsigned long *last_bp = last_frame(state);
        unsigned long *aligned_bp = last_aligned_frame(state);

        /*
         * GCC can occasionally decide to realign the stack pointer and change
         * the offset of the stack frame in the prologue of a function called
         * by head/entry code.  Examples:
         *
         * <start_secondary>:
         *      push   %edi
         *      lea    0x8(%esp),%edi
         *      and    $0xfffffff8,%esp
         *      pushl  -0x4(%edi)
         *      push   %ebp
         *      mov    %esp,%ebp
         *
         * <x86_64_start_kernel>:
         *      lea    0x8(%rsp),%r10
         *      and    $0xfffffffffffffff0,%rsp
         *      pushq  -0x8(%r10)
         *      push   %rbp
         *      mov    %rsp,%rbp
         *
         * After aligning the stack, it pushes a duplicate copy of the return
         * address before pushing the frame pointer.
         */
        return (state->bp == aligned_bp && *(aligned_bp + 1) == *(last_bp + 1));
}

static bool is_last_ftrace_frame(struct unwind_state *state)
{
        unsigned long *last_bp = last_frame(state);
        unsigned long *last_ftrace_bp = last_bp - 3;

        /*
         * When unwinding from an ftrace handler of a function called by entry
         * code, the stack layout of the last frame is:
         *
         *   bp
         *   parent ret addr
         *   bp
         *   function ret addr
         *   parent ret addr
         *   pt_regs
         *   -----------------
         */
        return (state->bp == last_ftrace_bp &&
                *state->bp == *(state->bp + 2) &&
                *(state->bp + 1) == *(state->bp + 4));
}

static bool is_last_task_frame(struct unwind_state *state)
{
        return is_last_frame(state) || is_last_aligned_frame(state) ||
               is_last_ftrace_frame(state);
}

/*
 * 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,
                               unsigned long *next_bp)
{
        struct stack_info *info = &state->stack_info;
        enum stack_type prev_type = info->type;
        struct pt_regs *regs;
        unsigned long *frame, *prev_frame_end, *addr_p, addr;
        size_t len;

        if (state->regs)
                prev_frame_end = (void *)state->regs + regs_size(state->regs);
        else
                prev_frame_end = (void *)state->bp + FRAME_HEADER_SIZE;

        /* Is the next frame pointer an encoded pointer to pt_regs? */
        regs = decode_frame_pointer(next_bp);
        if (regs) {
                frame = (unsigned long *)regs;
                len = regs_size(regs);
                state->got_irq = true;
        } else {
                frame = next_bp;
                len = FRAME_HEADER_SIZE;
        }

        /*
         * If the next bp 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 the next bp
         * could be on a subsequent stack.
         */
        while (!on_stack(info, frame, len))
                if (get_stack_info(info->next_sp, state->task, info,
                                   &state->stack_mask))
                        return false;

        /* Make sure it only unwinds up and doesn't overlap the prev frame: */
        if (state->orig_sp && state->stack_info.type == prev_type &&
            frame < prev_frame_end)
                return false;

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

        /* Save the return address: */
        if (state->regs && user_mode(state->regs))
                state->ip = 0;
        else {
                addr_p = unwind_get_return_address_ptr(state);
                addr = READ_ONCE_TASK_STACK(state->task, *addr_p);
                state->ip = ftrace_graph_ret_addr(state->task, &state->graph_idx,
                                                  addr, addr_p);
        }

        /* Save the original stack pointer for unwind_dump(): */
        if (!state->orig_sp)
                state->orig_sp = frame;

        return true;
}

bool unwind_next_frame(struct unwind_state *state)
{
        struct pt_regs *regs;
        unsigned long *next_bp;

        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;
                state->ip = 0;
                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);

        /* Move to the next frame if it's safe: */
        if (!update_stack_state(state, next_bp))
                goto bad_address;

        return true;

bad_address:
        state->error = true;

        /*
         * 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;

        /*
         * Don't warn if the unwinder got lost due to an interrupt in entry
         * code or in the C handler before the first frame pointer got set up:
         */
        if (state->got_irq && in_entry_code(state->ip))
                goto the_end;
        if (state->regs &&
            state->regs->sp >= (unsigned long)last_aligned_frame(state) &&
            state->regs->sp < (unsigned long)task_pt_regs(state->task))
                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_bp);
                unwind_dump(state);
        } 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_bp);
                unwind_dump(state);
        }
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;

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

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

        bp = get_frame_pointer(task, regs);

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

        /*
         * 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);