// SPDX-License-Identifier: GPL-2.0-or-later
/*
 *  Kernel Probes Jump Optimization (Optprobes)
 *
 * Copyright (C) IBM Corporation, 2002, 2004
 * Copyright (C) Hitachi Ltd., 2012
 */
#include <linux/kprobes.h>
#include <linux/perf_event.h>
#include <linux/ptrace.h>
#include <linux/string.h>
#include <linux/slab.h>
#include <linux/hardirq.h>
#include <linux/preempt.h>
#include <linux/extable.h>
#include <linux/kdebug.h>
#include <linux/kallsyms.h>
#include <linux/kgdb.h>
#include <linux/ftrace.h>
#include <linux/objtool.h>
#include <linux/pgtable.h>
#include <linux/static_call.h>

#include <asm/text-patching.h>
#include <asm/cacheflush.h>
#include <asm/desc.h>
#include <linux/uaccess.h>
#include <asm/alternative.h>
#include <asm/insn.h>
#include <asm/debugreg.h>
#include <asm/set_memory.h>
#include <asm/sections.h>
#include <asm/nospec-branch.h>

#include "common.h"

unsigned long __recover_optprobed_insn(kprobe_opcode_t *buf, unsigned long addr)
{
        struct optimized_kprobe *op;
        struct kprobe *kp;
        long offs;
        int i;

        for (i = 0; i < JMP32_INSN_SIZE; i++) {
                kp = get_kprobe((void *)addr - i);
                /* This function only handles jump-optimized kprobe */
                if (kp && kprobe_optimized(kp)) {
                        op = container_of(kp, struct optimized_kprobe, kp);
                        /* If op is optimized or under unoptimizing */
                        if (list_empty(&op->list) || optprobe_queued_unopt(op))
                                goto found;
                }
        }

        return addr;
found:
        /*
         * If the kprobe can be optimized, original bytes which can be
         * overwritten by jump destination address. In this case, original
         * bytes must be recovered from op->optinsn.copied_insn buffer.
         */
        if (copy_from_kernel_nofault(buf, (void *)addr,
                MAX_INSN_SIZE * sizeof(kprobe_opcode_t)))
                return 0UL;

        if (addr == (unsigned long)kp->addr) {
                buf[0] = kp->opcode;
                memcpy(buf + 1, op->optinsn.copied_insn, DISP32_SIZE);
        } else {
                offs = addr - (unsigned long)kp->addr - 1;
                memcpy(buf, op->optinsn.copied_insn + offs, DISP32_SIZE - offs);
        }

        return (unsigned long)buf;
}

static void synthesize_clac(kprobe_opcode_t *addr)
{
        /*
         * Can't be static_cpu_has() due to how objtool treats this feature bit.
         * This isn't a fast path anyway.
         */
        if (!boot_cpu_has(X86_FEATURE_SMAP))
                return;

        /* Replace the NOP3 with CLAC */
        addr[0] = 0x0f;
        addr[1] = 0x01;
        addr[2] = 0xca;
}

/* Insert a move instruction which sets a pointer to eax/rdi (1st arg). */
static void synthesize_set_arg1(kprobe_opcode_t *addr, unsigned long val)
{
#ifdef CONFIG_X86_64
        *addr++ = 0x48;
        *addr++ = 0xbf;
#else
        *addr++ = 0xb8;
#endif
        *(unsigned long *)addr = val;
}

asm (
                        ".pushsection .rodata\n"
                        ".global optprobe_template_entry\n"
                        "optprobe_template_entry:\n"
#ifdef CONFIG_X86_64
                        "       pushq $" __stringify(__KERNEL_DS) "\n"
                        /* Save the 'sp - 8', this will be fixed later. */
                        "       pushq %rsp\n"
                        "       pushfq\n"
                        ".global optprobe_template_clac\n"
                        "optprobe_template_clac:\n"
                        ASM_NOP3
                        SAVE_REGS_STRING
                        "       movq %rsp, %rsi\n"
                        ".global optprobe_template_val\n"
                        "optprobe_template_val:\n"
                        ASM_NOP5
                        ASM_NOP5
                        ".global optprobe_template_call\n"
                        "optprobe_template_call:\n"
                        ASM_NOP5
                        /* Copy 'regs->flags' into 'regs->ss'. */
                        "       movq 18*8(%rsp), %rdx\n"
                        "       movq %rdx, 20*8(%rsp)\n"
                        RESTORE_REGS_STRING
                        /* Skip 'regs->flags' and 'regs->sp'. */
                        "       addq $16, %rsp\n"
                        /* And pop flags register from 'regs->ss'. */
                        "       popfq\n"
#else /* CONFIG_X86_32 */
                        "       pushl %ss\n"
                        /* Save the 'sp - 4', this will be fixed later. */
                        "       pushl %esp\n"
                        "       pushfl\n"
                        ".global optprobe_template_clac\n"
                        "optprobe_template_clac:\n"
                        ASM_NOP3
                        SAVE_REGS_STRING
                        "       movl %esp, %edx\n"
                        ".global optprobe_template_val\n"
                        "optprobe_template_val:\n"
                        ASM_NOP5
                        ".global optprobe_template_call\n"
                        "optprobe_template_call:\n"
                        ASM_NOP5
                        /* Copy 'regs->flags' into 'regs->ss'. */
                        "       movl 14*4(%esp), %edx\n"
                        "       movl %edx, 16*4(%esp)\n"
                        RESTORE_REGS_STRING
                        /* Skip 'regs->flags' and 'regs->sp'. */
                        "       addl $8, %esp\n"
                        /* And pop flags register from 'regs->ss'. */
                        "       popfl\n"
#endif
                        ".global optprobe_template_end\n"
                        "optprobe_template_end:\n"
                        ".popsection\n");

#define TMPL_CLAC_IDX \
        ((long)optprobe_template_clac - (long)optprobe_template_entry)
#define TMPL_MOVE_IDX \
        ((long)optprobe_template_val - (long)optprobe_template_entry)
#define TMPL_CALL_IDX \
        ((long)optprobe_template_call - (long)optprobe_template_entry)
#define TMPL_END_IDX \
        ((long)optprobe_template_end - (long)optprobe_template_entry)

/* Optimized kprobe call back function: called from optinsn */
static void
optimized_callback(struct optimized_kprobe *op, struct pt_regs *regs)
{
        /* This is possible if op is under delayed unoptimizing */
        if (kprobe_disabled(&op->kp))
                return;

        preempt_disable();
        if (kprobe_running()) {
                kprobes_inc_nmissed_count(&op->kp);
        } else {
                struct kprobe_ctlblk *kcb = get_kprobe_ctlblk();
                /* Adjust stack pointer */
                regs->sp += sizeof(long);
                /* Save skipped registers */
                regs->cs = __KERNEL_CS;
#ifdef CONFIG_X86_32
                regs->gs = 0;
#endif
                regs->ip = (unsigned long)op->kp.addr + INT3_INSN_SIZE;
                regs->orig_ax = ~0UL;

                __this_cpu_write(current_kprobe, &op->kp);
                kcb->kprobe_status = KPROBE_HIT_ACTIVE;
                opt_pre_handler(&op->kp, regs);
                __this_cpu_write(current_kprobe, NULL);
        }
        preempt_enable();
}
NOKPROBE_SYMBOL(optimized_callback);

static int copy_optimized_instructions(u8 *dest, u8 *src, u8 *real)
{
        struct insn insn;
        int len = 0, ret;

        while (len < JMP32_INSN_SIZE) {
                ret = __copy_instruction(dest + len, src + len, real + len, &insn);
                if (!ret || !can_boost(&insn, src + len))
                        return -EINVAL;
                len += ret;
        }
        /* Check whether the address range is reserved */
        if (ftrace_text_reserved(src, src + len - 1) ||
            alternatives_text_reserved(src, src + len - 1) ||
            jump_label_text_reserved(src, src + len - 1) ||
            static_call_text_reserved(src, src + len - 1))
                return -EBUSY;

        return len;
}

/* Check whether insn is indirect jump */
static int insn_is_indirect_jump(struct insn *insn)
{
        return ((insn->opcode.bytes[0] == 0xff &&
                (X86_MODRM_REG(insn->modrm.value) & 6) == 4) || /* Jump */
                insn->opcode.bytes[0] == 0xea); /* Segment based jump */
}

/* Check whether insn jumps into specified address range */
static int insn_jump_into_range(struct insn *insn, unsigned long start, int len)
{
        unsigned long target = 0;

        switch (insn->opcode.bytes[0]) {
        case 0xe0:      /* loopne */
        case 0xe1:      /* loope */
        case 0xe2:      /* loop */
        case 0xe3:      /* jcxz */
        case 0xe9:      /* near relative jump */
        case 0xeb:      /* short relative jump */
                break;
        case 0x0f:
                if ((insn->opcode.bytes[1] & 0xf0) == 0x80) /* jcc near */
                        break;
                return 0;
        default:
                if ((insn->opcode.bytes[0] & 0xf0) == 0x70) /* jcc short */
                        break;
                return 0;
        }
        target = (unsigned long)insn->next_byte + insn->immediate.value;

        return (start <= target && target <= start + len);
}

/* Decode whole function to ensure any instructions don't jump into target */
static int can_optimize(unsigned long paddr)
{
        unsigned long addr, size = 0, offset = 0;
        struct insn insn;
        kprobe_opcode_t buf[MAX_INSN_SIZE];

        /* Lookup symbol including addr */
        if (!kallsyms_lookup_size_offset(paddr, &size, &offset))
                return 0;

        /*
         * Do not optimize in the entry code due to the unstable
         * stack handling and registers setup.
         */
        if (((paddr >= (unsigned long)__entry_text_start) &&
             (paddr <  (unsigned long)__entry_text_end)))
                return 0;

        /* Check there is enough space for a relative jump. */
        if (size - offset < JMP32_INSN_SIZE)
                return 0;

        /* Decode instructions */
        addr = paddr - offset;
        while (addr < paddr - offset + size) { /* Decode until function end */
                unsigned long recovered_insn;
                int ret;

                if (search_exception_tables(addr))
                        /*
                         * Since some fixup code will jumps into this function,
                         * we can't optimize kprobe in this function.
                         */
                        return 0;
                recovered_insn = recover_probed_instruction(buf, addr);
                if (!recovered_insn)
                        return 0;

                ret = insn_decode_kernel(&insn, (void *)recovered_insn);
                if (ret < 0)
                        return 0;
#ifdef CONFIG_KGDB
                /*
                 * If there is a dynamically installed kgdb sw breakpoint,
                 * this function should not be probed.
                 */
                if (insn.opcode.bytes[0] == INT3_INSN_OPCODE &&
                    kgdb_has_hit_break(addr))
                        return 0;
#endif
                /* Recover address */
                insn.kaddr = (void *)addr;
                insn.next_byte = (void *)(addr + insn.length);
                /*
                 * Check any instructions don't jump into target, indirectly or
                 * directly.
                 *
                 * The indirect case is present to handle a code with jump
                 * tables. When the kernel uses retpolines, the check should in
                 * theory additionally look for jumps to indirect thunks.
                 * However, the kernel built with retpolines or IBT has jump
                 * tables disabled so the check can be skipped altogether.
                 */
                if (!IS_ENABLED(CONFIG_MITIGATION_RETPOLINE) &&
                    !IS_ENABLED(CONFIG_X86_KERNEL_IBT) &&
                    insn_is_indirect_jump(&insn))
                        return 0;
                if (insn_jump_into_range(&insn, paddr + INT3_INSN_SIZE,
                                         DISP32_SIZE))
                        return 0;
                addr += insn.length;
        }

        return 1;
}

/* Check optimized_kprobe can actually be optimized. */
int arch_check_optimized_kprobe(struct optimized_kprobe *op)
{
        int i;
        struct kprobe *p;

        for (i = 1; i < op->optinsn.size; i++) {
                p = get_kprobe(op->kp.addr + i);
                if (p && !kprobe_disarmed(p))
                        return -EEXIST;
        }

        return 0;
}

/* Check the addr is within the optimized instructions. */
int arch_within_optimized_kprobe(struct optimized_kprobe *op,
                                 kprobe_opcode_t *addr)
{
        return (op->kp.addr <= addr &&
                op->kp.addr + op->optinsn.size > addr);
}

/* Free optimized instruction slot */
static
void __arch_remove_optimized_kprobe(struct optimized_kprobe *op, int dirty)
{
        u8 *slot = op->optinsn.insn;
        if (slot) {
                int len = TMPL_END_IDX + op->optinsn.size + JMP32_INSN_SIZE;

                /* Record the perf event before freeing the slot */
                if (dirty)
                        perf_event_text_poke(slot, slot, len, NULL, 0);

                free_optinsn_slot(slot, dirty);
                op->optinsn.insn = NULL;
                op->optinsn.size = 0;
        }
}

void arch_remove_optimized_kprobe(struct optimized_kprobe *op)
{
        __arch_remove_optimized_kprobe(op, 1);
}

/*
 * Copy replacing target instructions
 * Target instructions MUST be relocatable (checked inside)
 * This is called when new aggr(opt)probe is allocated or reused.
 */
int arch_prepare_optimized_kprobe(struct optimized_kprobe *op,
                                  struct kprobe *__unused)
{
        u8 *buf = NULL, *slot;
        int ret, len;
        long rel;

        if (!can_optimize((unsigned long)op->kp.addr))
                return -EILSEQ;

        buf = kzalloc(MAX_OPTINSN_SIZE, GFP_KERNEL);
        if (!buf)
                return -ENOMEM;

        op->optinsn.insn = slot = get_optinsn_slot();
        if (!slot) {
                ret = -ENOMEM;
                goto out;
        }

        /*
         * Verify if the address gap is in 2GB range, because this uses
         * a relative jump.
         */
        rel = (long)slot - (long)op->kp.addr + JMP32_INSN_SIZE;
        if (abs(rel) > 0x7fffffff) {
                ret = -ERANGE;
                goto err;
        }

        /* Copy arch-dep-instance from template */
        memcpy(buf, optprobe_template_entry, TMPL_END_IDX);

        /* Copy instructions into the out-of-line buffer */
        ret = copy_optimized_instructions(buf + TMPL_END_IDX, op->kp.addr,
                                          slot + TMPL_END_IDX);
        if (ret < 0)
                goto err;
        op->optinsn.size = ret;
        len = TMPL_END_IDX + op->optinsn.size;

        synthesize_clac(buf + TMPL_CLAC_IDX);

        /* Set probe information */
        synthesize_set_arg1(buf + TMPL_MOVE_IDX, (unsigned long)op);

        /* Set probe function call */
        synthesize_relcall(buf + TMPL_CALL_IDX,
                           slot + TMPL_CALL_IDX, optimized_callback);

        /* Set returning jmp instruction at the tail of out-of-line buffer */
        synthesize_reljump(buf + len, slot + len,
                           (u8 *)op->kp.addr + op->optinsn.size);
        len += JMP32_INSN_SIZE;

        /*
         * Note len = TMPL_END_IDX + op->optinsn.size + JMP32_INSN_SIZE is also
         * used in __arch_remove_optimized_kprobe().
         */

        /* We have to use text_poke() for instruction buffer because it is RO */
        perf_event_text_poke(slot, NULL, 0, buf, len);
        text_poke(slot, buf, len);

        ret = 0;
out:
        kfree(buf);
        return ret;

err:
        __arch_remove_optimized_kprobe(op, 0);
        goto out;
}

/*
 * Replace breakpoints (INT3) with relative jumps (JMP.d32).
 * Caller must call with locking kprobe_mutex and text_mutex.
 *
 * The caller will have installed a regular kprobe and after that issued
 * syncrhonize_rcu_tasks(), this ensures that the instruction(s) that live in
 * the 4 bytes after the INT3 are unused and can now be overwritten.
 */
void arch_optimize_kprobes(struct list_head *oplist)
{
        struct optimized_kprobe *op, *tmp;
        u8 insn_buff[JMP32_INSN_SIZE];

        list_for_each_entry_safe(op, tmp, oplist, list) {
                s32 rel = (s32)((long)op->optinsn.insn -
                        ((long)op->kp.addr + JMP32_INSN_SIZE));

                WARN_ON(kprobe_disabled(&op->kp));

                /* Backup instructions which will be replaced by jump address */
                memcpy(op->optinsn.copied_insn, op->kp.addr + INT3_INSN_SIZE,
                       DISP32_SIZE);

                insn_buff[0] = JMP32_INSN_OPCODE;
                *(s32 *)(&insn_buff[1]) = rel;

                smp_text_poke_single(op->kp.addr, insn_buff, JMP32_INSN_SIZE, NULL);

                list_del_init(&op->list);
        }
}

/*
 * Replace a relative jump (JMP.d32) with a breakpoint (INT3).
 *
 * After that, we can restore the 4 bytes after the INT3 to undo what
 * arch_optimize_kprobes() scribbled. This is safe since those bytes will be
 * unused once the INT3 lands.
 */
void arch_unoptimize_kprobe(struct optimized_kprobe *op)
{
        u8 new[JMP32_INSN_SIZE] = { INT3_INSN_OPCODE, };
        u8 old[JMP32_INSN_SIZE];
        u8 *addr = op->kp.addr;

        memcpy(old, op->kp.addr, JMP32_INSN_SIZE);
        memcpy(new + INT3_INSN_SIZE,
               op->optinsn.copied_insn,
               JMP32_INSN_SIZE - INT3_INSN_SIZE);

        text_poke(addr, new, INT3_INSN_SIZE);
        smp_text_poke_sync_each_cpu();
        text_poke(addr + INT3_INSN_SIZE,
                  new + INT3_INSN_SIZE,
                  JMP32_INSN_SIZE - INT3_INSN_SIZE);
        smp_text_poke_sync_each_cpu();

        perf_event_text_poke(op->kp.addr, old, JMP32_INSN_SIZE, new, JMP32_INSN_SIZE);
}

/*
 * Recover original instructions and breakpoints from relative jumps.
 * Caller must call with locking kprobe_mutex.
 */
extern void arch_unoptimize_kprobes(struct list_head *oplist,
                                    struct list_head *done_list)
{
        struct optimized_kprobe *op, *tmp;

        list_for_each_entry_safe(op, tmp, oplist, list) {
                arch_unoptimize_kprobe(op);
                list_move(&op->list, done_list);
        }
}

int setup_detour_execution(struct kprobe *p, struct pt_regs *regs, int reenter)
{
        struct optimized_kprobe *op;

        if (p->flags & KPROBE_FLAG_OPTIMIZED) {
                /* This kprobe is really able to run optimized path. */
                op = container_of(p, struct optimized_kprobe, kp);
                /* Detour through copied instructions */
                regs->ip = (unsigned long)op->optinsn.insn + TMPL_END_IDX;
                if (!reenter)
                        reset_current_kprobe();
                return 1;
        }
        return 0;
}
NOKPROBE_SYMBOL(setup_detour_execution);