x86/unwind/orc: Prevent unwinding before ORC initialization

[mirror_ubuntu-jammy-kernel.git] / arch / x86 / kernel / unwind_orc.c

// SPDX-License-Identifier: GPL-2.0-only
#include <linux/module.h>
#include <linux/sort.h>
#include <asm/ptrace.h>
#include <asm/stacktrace.h>
#include <asm/unwind.h>
#include <asm/orc_types.h>
#include <asm/orc_lookup.h>

#define orc_warn(fmt, ...) \
        printk_deferred_once(KERN_WARNING "WARNING: " fmt, ##__VA_ARGS__)

#define orc_warn_current(args...)                                       \
({                                                                      \
        if (state->task == current)                                     \
                orc_warn(args);                                         \
})

extern int __start_orc_unwind_ip[];
extern int __stop_orc_unwind_ip[];
extern struct orc_entry __start_orc_unwind[];
extern struct orc_entry __stop_orc_unwind[];

static bool orc_init __ro_after_init;
static unsigned int lookup_num_blocks __ro_after_init;

static DEFINE_MUTEX(sort_mutex);
static int *cur_orc_ip_table = __start_orc_unwind_ip;
static struct orc_entry *cur_orc_table = __start_orc_unwind;

static inline unsigned long orc_ip(const int *ip)
{
        return (unsigned long)ip + *ip;
}

static struct orc_entry *__orc_find(int *ip_table, struct orc_entry *u_table,
                                    unsigned int num_entries, unsigned long ip)
{
        int *first = ip_table;
        int *last = ip_table + num_entries - 1;
        int *mid = first, *found = first;

        if (!num_entries)
                return NULL;

        /*
         * Do a binary range search to find the rightmost duplicate of a given
         * starting address.  Some entries are section terminators which are
         * "weak" entries for ensuring there are no gaps.  They should be
         * ignored when they conflict with a real entry.
         */
        while (first <= last) {
                mid = first + ((last - first) / 2);

                if (orc_ip(mid) <= ip) {
                        found = mid;
                        first = mid + 1;
                } else
                        last = mid - 1;
        }

        return u_table + (found - ip_table);
}

#ifdef CONFIG_MODULES
static struct orc_entry *orc_module_find(unsigned long ip)
{
        struct module *mod;

        mod = __module_address(ip);
        if (!mod || !mod->arch.orc_unwind || !mod->arch.orc_unwind_ip)
                return NULL;
        return __orc_find(mod->arch.orc_unwind_ip, mod->arch.orc_unwind,
                          mod->arch.num_orcs, ip);
}
#else
static struct orc_entry *orc_module_find(unsigned long ip)
{
        return NULL;
}
#endif

#ifdef CONFIG_DYNAMIC_FTRACE
static struct orc_entry *orc_find(unsigned long ip);

/*
 * Ftrace dynamic trampolines do not have orc entries of their own.
 * But they are copies of the ftrace entries that are static and
 * defined in ftrace_*.S, which do have orc entries.
 *
 * If the unwinder comes across a ftrace trampoline, then find the
 * ftrace function that was used to create it, and use that ftrace
 * function's orc entry, as the placement of the return code in
 * the stack will be identical.
 */
static struct orc_entry *orc_ftrace_find(unsigned long ip)
{
        struct ftrace_ops *ops;
        unsigned long caller;

        ops = ftrace_ops_trampoline(ip);
        if (!ops)
                return NULL;

        if (ops->flags & FTRACE_OPS_FL_SAVE_REGS)
                caller = (unsigned long)ftrace_regs_call;
        else
                caller = (unsigned long)ftrace_call;

        /* Prevent unlikely recursion */
        if (ip == caller)
                return NULL;

        return orc_find(caller);
}
#else
static struct orc_entry *orc_ftrace_find(unsigned long ip)
{
        return NULL;
}
#endif

/*
 * If we crash with IP==0, the last successfully executed instruction
 * was probably an indirect function call with a NULL function pointer,
 * and we don't have unwind information for NULL.
 * This hardcoded ORC entry for IP==0 allows us to unwind from a NULL function
 * pointer into its parent and then continue normally from there.
 */
static struct orc_entry null_orc_entry = {
        .sp_offset = sizeof(long),
        .sp_reg = ORC_REG_SP,
        .bp_reg = ORC_REG_UNDEFINED,
        .type = ORC_TYPE_CALL
};

/* Fake frame pointer entry -- used as a fallback for generated code */
static struct orc_entry orc_fp_entry = {
        .type           = ORC_TYPE_CALL,
        .sp_reg         = ORC_REG_BP,
        .sp_offset      = 16,
        .bp_reg         = ORC_REG_PREV_SP,
        .bp_offset      = -16,
        .end            = 0,
};

static struct orc_entry *orc_find(unsigned long ip)
{
        static struct orc_entry *orc;

        if (ip == 0)
                return &null_orc_entry;

        /* For non-init vmlinux addresses, use the fast lookup table: */
        if (ip >= LOOKUP_START_IP && ip < LOOKUP_STOP_IP) {
                unsigned int idx, start, stop;

                idx = (ip - LOOKUP_START_IP) / LOOKUP_BLOCK_SIZE;

                if (unlikely((idx >= lookup_num_blocks-1))) {
                        orc_warn("WARNING: bad lookup idx: idx=%u num=%u ip=%pB\n",
                                 idx, lookup_num_blocks, (void *)ip);
                        return NULL;
                }

                start = orc_lookup[idx];
                stop = orc_lookup[idx + 1] + 1;

                if (unlikely((__start_orc_unwind + start >= __stop_orc_unwind) ||
                             (__start_orc_unwind + stop > __stop_orc_unwind))) {
                        orc_warn("WARNING: bad lookup value: idx=%u num=%u start=%u stop=%u ip=%pB\n",
                                 idx, lookup_num_blocks, start, stop, (void *)ip);
                        return NULL;
                }

                return __orc_find(__start_orc_unwind_ip + start,
                                  __start_orc_unwind + start, stop - start, ip);
        }

        /* vmlinux .init slow lookup: */
        if (init_kernel_text(ip))
                return __orc_find(__start_orc_unwind_ip, __start_orc_unwind,
                                  __stop_orc_unwind_ip - __start_orc_unwind_ip, ip);

        /* Module lookup: */
        orc = orc_module_find(ip);
        if (orc)
                return orc;

        return orc_ftrace_find(ip);
}

#ifdef CONFIG_MODULES

static void orc_sort_swap(void *_a, void *_b, int size)
{
        struct orc_entry *orc_a, *orc_b;
        struct orc_entry orc_tmp;
        int *a = _a, *b = _b, tmp;
        int delta = _b - _a;

        /* Swap the .orc_unwind_ip entries: */
        tmp = *a;
        *a = *b + delta;
        *b = tmp - delta;

        /* Swap the corresponding .orc_unwind entries: */
        orc_a = cur_orc_table + (a - cur_orc_ip_table);
        orc_b = cur_orc_table + (b - cur_orc_ip_table);
        orc_tmp = *orc_a;
        *orc_a = *orc_b;
        *orc_b = orc_tmp;
}

static int orc_sort_cmp(const void *_a, const void *_b)
{
        struct orc_entry *orc_a;
        const int *a = _a, *b = _b;
        unsigned long a_val = orc_ip(a);
        unsigned long b_val = orc_ip(b);

        if (a_val > b_val)
                return 1;
        if (a_val < b_val)
                return -1;

        /*
         * The "weak" section terminator entries need to always be on the left
         * to ensure the lookup code skips them in favor of real entries.
         * These terminator entries exist to handle any gaps created by
         * whitelisted .o files which didn't get objtool generation.
         */
        orc_a = cur_orc_table + (a - cur_orc_ip_table);
        return orc_a->sp_reg == ORC_REG_UNDEFINED && !orc_a->end ? -1 : 1;
}

void unwind_module_init(struct module *mod, void *_orc_ip, size_t orc_ip_size,
                        void *_orc, size_t orc_size)
{
        int *orc_ip = _orc_ip;
        struct orc_entry *orc = _orc;
        unsigned int num_entries = orc_ip_size / sizeof(int);

        WARN_ON_ONCE(orc_ip_size % sizeof(int) != 0 ||
                     orc_size % sizeof(*orc) != 0 ||
                     num_entries != orc_size / sizeof(*orc));

        /*
         * The 'cur_orc_*' globals allow the orc_sort_swap() callback to
         * associate an .orc_unwind_ip table entry with its corresponding
         * .orc_unwind entry so they can both be swapped.
         */
        mutex_lock(&sort_mutex);
        cur_orc_ip_table = orc_ip;
        cur_orc_table = orc;
        sort(orc_ip, num_entries, sizeof(int), orc_sort_cmp, orc_sort_swap);
        mutex_unlock(&sort_mutex);

        mod->arch.orc_unwind_ip = orc_ip;
        mod->arch.orc_unwind = orc;
        mod->arch.num_orcs = num_entries;
}
#endif

void __init unwind_init(void)
{
        size_t orc_ip_size = (void *)__stop_orc_unwind_ip - (void *)__start_orc_unwind_ip;
        size_t orc_size = (void *)__stop_orc_unwind - (void *)__start_orc_unwind;
        size_t num_entries = orc_ip_size / sizeof(int);
        struct orc_entry *orc;
        int i;

        if (!num_entries || orc_ip_size % sizeof(int) != 0 ||
            orc_size % sizeof(struct orc_entry) != 0 ||
            num_entries != orc_size / sizeof(struct orc_entry)) {
                orc_warn("WARNING: Bad or missing .orc_unwind table.  Disabling unwinder.\n");
                return;
        }

        /*
         * Note, the orc_unwind and orc_unwind_ip tables were already
         * sorted at build time via the 'sorttable' tool.
         * It's ready for binary search straight away, no need to sort it.
         */

        /* Initialize the fast lookup table: */
        lookup_num_blocks = orc_lookup_end - orc_lookup;
        for (i = 0; i < lookup_num_blocks-1; i++) {
                orc = __orc_find(__start_orc_unwind_ip, __start_orc_unwind,
                                 num_entries,
                                 LOOKUP_START_IP + (LOOKUP_BLOCK_SIZE * i));
                if (!orc) {
                        orc_warn("WARNING: Corrupt .orc_unwind table.  Disabling unwinder.\n");
                        return;
                }

                orc_lookup[i] = orc - __start_orc_unwind;
        }

        /* Initialize the ending block: */
        orc = __orc_find(__start_orc_unwind_ip, __start_orc_unwind, num_entries,
                         LOOKUP_STOP_IP);
        if (!orc) {
                orc_warn("WARNING: Corrupt .orc_unwind table.  Disabling unwinder.\n");
                return;
        }
        orc_lookup[lookup_num_blocks-1] = orc - __start_orc_unwind;

        orc_init = true;
}

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);

unsigned long *unwind_get_return_address_ptr(struct unwind_state *state)
{
        if (unwind_done(state))
                return NULL;

        if (state->regs)
                return &state->regs->ip;

        if (state->sp)
                return (unsigned long *)state->sp - 1;

        return NULL;
}

static bool stack_access_ok(struct unwind_state *state, unsigned long _addr,
                            size_t len)
{
        struct stack_info *info = &state->stack_info;
        void *addr = (void *)_addr;

        if (!on_stack(info, addr, len) &&
            (get_stack_info(addr, state->task, info, &state->stack_mask)))
                return false;

        return true;
}

static bool deref_stack_reg(struct unwind_state *state, unsigned long addr,
                            unsigned long *val)
{
        if (!stack_access_ok(state, addr, sizeof(long)))
                return false;

        *val = READ_ONCE_NOCHECK(*(unsigned long *)addr);
        return true;
}

static bool deref_stack_regs(struct unwind_state *state, unsigned long addr,
                             unsigned long *ip, unsigned long *sp)
{
        struct pt_regs *regs = (struct pt_regs *)addr;

        /* x86-32 support will be more complicated due to the &regs->sp hack */
        BUILD_BUG_ON(IS_ENABLED(CONFIG_X86_32));

        if (!stack_access_ok(state, addr, sizeof(struct pt_regs)))
                return false;

        *ip = regs->ip;
        *sp = regs->sp;
        return true;
}

static bool deref_stack_iret_regs(struct unwind_state *state, unsigned long addr,
                                  unsigned long *ip, unsigned long *sp)
{
        struct pt_regs *regs = (void *)addr - IRET_FRAME_OFFSET;

        if (!stack_access_ok(state, addr, IRET_FRAME_SIZE))
                return false;

        *ip = regs->ip;
        *sp = regs->sp;
        return true;
}

bool unwind_next_frame(struct unwind_state *state)
{
        unsigned long ip_p, sp, orig_ip = state->ip, prev_sp = state->sp;
        enum stack_type prev_type = state->stack_info.type;
        struct orc_entry *orc;
        bool indirect = false;

        if (unwind_done(state))
                return false;

        /* Don't let modules unload while we're reading their ORC data. */
        preempt_disable();

        /* End-of-stack check for user tasks: */
        if (state->regs && user_mode(state->regs))
                goto the_end;

        /*
         * Find the orc_entry associated with the text address.
         *
         * Decrement call return addresses by one so they work for sibling
         * calls and calls to noreturn functions.
         */
        orc = orc_find(state->signal ? state->ip : state->ip - 1);
        if (!orc) {
                /*
                 * As a fallback, try to assume this code uses a frame pointer.
                 * This is useful for generated code, like BPF, which ORC
                 * doesn't know about.  This is just a guess, so the rest of
                 * the unwind is no longer considered reliable.
                 */
                orc = &orc_fp_entry;
                state->error = true;
        }

        /* End-of-stack check for kernel threads: */
        if (orc->sp_reg == ORC_REG_UNDEFINED) {
                if (!orc->end)
                        goto err;

                goto the_end;
        }

        /* Find the previous frame's stack: */
        switch (orc->sp_reg) {
        case ORC_REG_SP:
                sp = state->sp + orc->sp_offset;
                break;

        case ORC_REG_BP:
                sp = state->bp + orc->sp_offset;
                break;

        case ORC_REG_SP_INDIRECT:
                sp = state->sp + orc->sp_offset;
                indirect = true;
                break;

        case ORC_REG_BP_INDIRECT:
                sp = state->bp + orc->sp_offset;
                indirect = true;
                break;

        case ORC_REG_R10:
                if (!state->regs || !state->full_regs) {
                        orc_warn_current("missing R10 value at %pB\n",
                                         (void *)state->ip);
                        goto err;
                }
                sp = state->regs->r10;
                break;

        case ORC_REG_R13:
                if (!state->regs || !state->full_regs) {
                        orc_warn_current("missing R13 value at %pB\n",
                                         (void *)state->ip);
                        goto err;
                }
                sp = state->regs->r13;
                break;

        case ORC_REG_DI:
                if (!state->regs || !state->full_regs) {
                        orc_warn_current("missing RDI value at %pB\n",
                                         (void *)state->ip);
                        goto err;
                }
                sp = state->regs->di;
                break;

        case ORC_REG_DX:
                if (!state->regs || !state->full_regs) {
                        orc_warn_current("missing DX value at %pB\n",
                                         (void *)state->ip);
                        goto err;
                }
                sp = state->regs->dx;
                break;

        default:
                orc_warn("unknown SP base reg %d at %pB\n",
                         orc->sp_reg, (void *)state->ip);
                goto err;
        }

        if (indirect) {
                if (!deref_stack_reg(state, sp, &sp))
                        goto err;
        }

        /* Find IP, SP and possibly regs: */
        switch (orc->type) {
        case ORC_TYPE_CALL:
                ip_p = sp - sizeof(long);

                if (!deref_stack_reg(state, ip_p, &state->ip))
                        goto err;

                state->ip = ftrace_graph_ret_addr(state->task, &state->graph_idx,
                                                  state->ip, (void *)ip_p);

                state->sp = sp;
                state->regs = NULL;
                state->signal = false;
                break;

        case ORC_TYPE_REGS:
                if (!deref_stack_regs(state, sp, &state->ip, &state->sp)) {
                        orc_warn_current("can't access registers at %pB\n",
                                         (void *)orig_ip);
                        goto err;
                }

                state->regs = (struct pt_regs *)sp;
                state->full_regs = true;
                state->signal = true;
                break;

        case ORC_TYPE_REGS_IRET:
                if (!deref_stack_iret_regs(state, sp, &state->ip, &state->sp)) {
                        orc_warn_current("can't access iret registers at %pB\n",
                                         (void *)orig_ip);
                        goto err;
                }

                state->regs = (void *)sp - IRET_FRAME_OFFSET;
                state->full_regs = false;
                state->signal = true;
                break;

        default:
                orc_warn("unknown .orc_unwind entry type %d at %pB\n",
                         orc->type, (void *)orig_ip);
                break;
        }

        /* Find BP: */
        switch (orc->bp_reg) {
        case ORC_REG_UNDEFINED:
                if (state->regs && state->full_regs)
                        state->bp = state->regs->bp;
                break;

        case ORC_REG_PREV_SP:
                if (!deref_stack_reg(state, sp + orc->bp_offset, &state->bp))
                        goto err;
                break;

        case ORC_REG_BP:
                if (!deref_stack_reg(state, state->bp + orc->bp_offset, &state->bp))
                        goto err;
                break;

        default:
                orc_warn("unknown BP base reg %d for ip %pB\n",
                         orc->bp_reg, (void *)orig_ip);
                goto err;
        }

        /* Prevent a recursive loop due to bad ORC data: */
        if (state->stack_info.type == prev_type &&
            on_stack(&state->stack_info, (void *)state->sp, sizeof(long)) &&
            state->sp <= prev_sp) {
                orc_warn_current("stack going in the wrong direction? at %pB\n",
                                 (void *)orig_ip);
                goto err;
        }

        preempt_enable();
        return true;

err:
        state->error = true;

the_end:
        preempt_enable();
        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)
{
        if (!orc_init)
                goto done;

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

        /*
         * Refuse to unwind the stack of a task while it's executing on another
         * CPU.  This check is racy, but that's ok: the unwinder has other
         * checks to prevent it from going off the rails.
         */
        if (task_on_another_cpu(task))
                goto done;

        if (regs) {
                if (user_mode(regs))
                        goto done;

                state->ip = regs->ip;
                state->sp = regs->sp;
                state->bp = regs->bp;
                state->regs = regs;
                state->full_regs = true;
                state->signal = true;

        } else if (task == current) {
                asm volatile("lea (%%rip), %0\n\t"
                             "mov %%rsp, %1\n\t"
                             "mov %%rbp, %2\n\t"
                             : "=r" (state->ip), "=r" (state->sp),
                               "=r" (state->bp));

        } else {
                struct inactive_task_frame *frame = (void *)task->thread.sp;

                state->sp = task->thread.sp;
                state->bp = READ_ONCE_NOCHECK(frame->bp);
                state->ip = READ_ONCE_NOCHECK(frame->ret_addr);
        }

        if (get_stack_info((unsigned long *)state->sp, state->task,
                           &state->stack_info, &state->stack_mask)) {
                /*
                 * We weren't on a valid stack.  It's possible that
                 * we overflowed a valid stack into a guard page.
                 * See if the next page up is valid so that we can
                 * generate some kind of backtrace if this happens.
                 */
                void *next_page = (void *)PAGE_ALIGN((unsigned long)state->sp);
                if (get_stack_info(next_page, state->task, &state->stack_info,
                                   &state->stack_mask))
                        return;
        }

        /*
         * 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.
         */

        /* When starting from regs, skip the regs frame: */
        if (regs) {
                unwind_next_frame(state);
                return;
        }

        /* Otherwise, skip ahead to the user-specified starting frame: */
        while (!unwind_done(state) &&
               (!on_stack(&state->stack_info, first_frame, sizeof(long)) ||
                        state->sp < (unsigned long)first_frame))
                unwind_next_frame(state);

        return;

done:
        state->stack_info.type = STACK_TYPE_UNKNOWN;
        return;
}
EXPORT_SYMBOL_GPL(__unwind_start);