// SPDX-License-Identifier: GPL-2.0
/*
 * Copyright (C) 2008 Matt Fleming <matt@console-pimps.org>
 * Copyright (C) 2008 Paul Mundt <lethal@linux-sh.org>
 *
 * Code for replacing ftrace calls with jumps.
 *
 * Copyright (C) 2007-2008 Steven Rostedt <srostedt@redhat.com>
 *
 * Thanks goes to Ingo Molnar, for suggesting the idea.
 * Mathieu Desnoyers, for suggesting postponing the modifications.
 * Arjan van de Ven, for keeping me straight, and explaining to me
 * the dangers of modifying code on the run.
 */
#include <linux/uaccess.h>
#include <linux/ftrace.h>
#include <linux/string.h>
#include <linux/init.h>
#include <linux/io.h>
#include <linux/kernel.h>
#include <asm/ftrace.h>
#include <asm/cacheflush.h>
#include <asm/unistd.h>
#include <trace/syscall.h>

#ifdef CONFIG_DYNAMIC_FTRACE
static unsigned char ftrace_replaced_code[MCOUNT_INSN_SIZE];

static unsigned char ftrace_nop[4];
/*
 * If we're trying to nop out a call to a function, we instead
 * place a call to the address after the memory table.
 *
 * 8c011060 <a>:
 * 8c011060:       02 d1           mov.l   8c01106c <a+0xc>,r1
 * 8c011062:       22 4f           sts.l   pr,@-r15
 * 8c011064:       02 c7           mova    8c011070 <a+0x10>,r0
 * 8c011066:       2b 41           jmp     @r1
 * 8c011068:       2a 40           lds     r0,pr
 * 8c01106a:       09 00           nop
 * 8c01106c:       68 24           .word 0x2468     <--- ip
 * 8c01106e:       1d 8c           .word 0x8c1d
 * 8c011070:       26 4f           lds.l   @r15+,pr <--- ip + MCOUNT_INSN_SIZE
 *
 * We write 0x8c011070 to 0x8c01106c so that on entry to a() we branch
 * past the _mcount call and continue executing code like normal.
 */
static unsigned char *ftrace_nop_replace(unsigned long ip)
{
        __raw_writel(ip + MCOUNT_INSN_SIZE, ftrace_nop);
        return ftrace_nop;
}

static unsigned char *ftrace_call_replace(unsigned long ip, unsigned long addr)
{
        /* Place the address in the memory table. */
        __raw_writel(addr, ftrace_replaced_code);

        /*
         * No locking needed, this must be called via kstop_machine
         * which in essence is like running on a uniprocessor machine.
         */
        return ftrace_replaced_code;
}

/*
 * Modifying code must take extra care. On an SMP machine, if
 * the code being modified is also being executed on another CPU
 * that CPU will have undefined results and possibly take a GPF.
 * We use kstop_machine to stop other CPUS from executing code.
 * But this does not stop NMIs from happening. We still need
 * to protect against that. We separate out the modification of
 * the code to take care of this.
 *
 * Two buffers are added: An IP buffer and a "code" buffer.
 *
 * 1) Put the instruction pointer into the IP buffer
 *    and the new code into the "code" buffer.
 * 2) Wait for any running NMIs to finish and set a flag that says
 *    we are modifying code, it is done in an atomic operation.
 * 3) Write the code
 * 4) clear the flag.
 * 5) Wait for any running NMIs to finish.
 *
 * If an NMI is executed, the first thing it does is to call
 * "ftrace_nmi_enter". This will check if the flag is set to write
 * and if it is, it will write what is in the IP and "code" buffers.
 *
 * The trick is, it does not matter if everyone is writing the same
 * content to the code location. Also, if a CPU is executing code
 * it is OK to write to that code location if the contents being written
 * are the same as what exists.
 */
#define MOD_CODE_WRITE_FLAG (1 << 31)   /* set when NMI should do the write */
static atomic_t nmi_running = ATOMIC_INIT(0);
static int mod_code_status;             /* holds return value of text write */
static void *mod_code_ip;               /* holds the IP to write to */
static void *mod_code_newcode;          /* holds the text to write to the IP */

static void clear_mod_flag(void)
{
        int old = atomic_read(&nmi_running);

        for (;;) {
                int new = old & ~MOD_CODE_WRITE_FLAG;

                if (old == new)
                        break;

                old = atomic_cmpxchg(&nmi_running, old, new);
        }
}

static void ftrace_mod_code(void)
{
        /*
         * Yes, more than one CPU process can be writing to mod_code_status.
         *    (and the code itself)
         * But if one were to fail, then they all should, and if one were
         * to succeed, then they all should.
         */
        mod_code_status = copy_to_kernel_nofault(mod_code_ip, mod_code_newcode,
                                             MCOUNT_INSN_SIZE);

        /* if we fail, then kill any new writers */
        if (mod_code_status)
                clear_mod_flag();
}

void arch_ftrace_nmi_enter(void)
{
        if (atomic_inc_return(&nmi_running) & MOD_CODE_WRITE_FLAG) {
                smp_rmb();
                ftrace_mod_code();
        }
        /* Must have previous changes seen before executions */
        smp_mb();
}

void arch_ftrace_nmi_exit(void)
{
        /* Finish all executions before clearing nmi_running */
        smp_mb();
        atomic_dec(&nmi_running);
}

static void wait_for_nmi_and_set_mod_flag(void)
{
        if (!atomic_cmpxchg(&nmi_running, 0, MOD_CODE_WRITE_FLAG))
                return;

        do {
                cpu_relax();
        } while (atomic_cmpxchg(&nmi_running, 0, MOD_CODE_WRITE_FLAG));
}

static void wait_for_nmi(void)
{
        if (!atomic_read(&nmi_running))
                return;

        do {
                cpu_relax();
        } while (atomic_read(&nmi_running));
}

static int
do_ftrace_mod_code(unsigned long ip, void *new_code)
{
        mod_code_ip = (void *)ip;
        mod_code_newcode = new_code;

        /* The buffers need to be visible before we let NMIs write them */
        smp_mb();

        wait_for_nmi_and_set_mod_flag();

        /* Make sure all running NMIs have finished before we write the code */
        smp_mb();

        ftrace_mod_code();

        /* Make sure the write happens before clearing the bit */
        smp_mb();

        clear_mod_flag();
        wait_for_nmi();

        return mod_code_status;
}

static int ftrace_modify_code(unsigned long ip, unsigned char *old_code,
                       unsigned char *new_code)
{
        unsigned char replaced[MCOUNT_INSN_SIZE];

        /*
         * Note:
         * We are paranoid about modifying text, as if a bug was to happen, it
         * could cause us to read or write to someplace that could cause harm.
         * Carefully read and modify the code with probe_kernel_*(), and make
         * sure what we read is what we expected it to be before modifying it.
         */

        /* read the text we want to modify */
        if (copy_from_kernel_nofault(replaced, (void *)ip, MCOUNT_INSN_SIZE))
                return -EFAULT;

        /* Make sure it is what we expect it to be */
        if (memcmp(replaced, old_code, MCOUNT_INSN_SIZE) != 0)
                return -EINVAL;

        /* replace the text with the new text */
        if (do_ftrace_mod_code(ip, new_code))
                return -EPERM;

        flush_icache_range(ip, ip + MCOUNT_INSN_SIZE);

        return 0;
}

int ftrace_update_ftrace_func(ftrace_func_t func)
{
        unsigned long ip = (unsigned long)(&ftrace_call) + MCOUNT_INSN_OFFSET;
        unsigned char old[MCOUNT_INSN_SIZE], *new;

        memcpy(old, (unsigned char *)ip, MCOUNT_INSN_SIZE);
        new = ftrace_call_replace(ip, (unsigned long)func);

        return ftrace_modify_code(ip, old, new);
}

int ftrace_make_nop(struct module *mod,
                    struct dyn_ftrace *rec, unsigned long addr)
{
        unsigned char *new, *old;
        unsigned long ip = rec->ip;

        old = ftrace_call_replace(ip, addr);
        new = ftrace_nop_replace(ip);

        return ftrace_modify_code(rec->ip, old, new);
}

int ftrace_make_call(struct dyn_ftrace *rec, unsigned long addr)
{
        unsigned char *new, *old;
        unsigned long ip = rec->ip;

        old = ftrace_nop_replace(ip);
        new = ftrace_call_replace(ip, addr);

        return ftrace_modify_code(rec->ip, old, new);
}
#endif /* CONFIG_DYNAMIC_FTRACE */

#ifdef CONFIG_FUNCTION_GRAPH_TRACER
#ifdef CONFIG_DYNAMIC_FTRACE
extern void ftrace_graph_call(void);

static int ftrace_mod(unsigned long ip, unsigned long old_addr,
                      unsigned long new_addr)
{
        unsigned char code[MCOUNT_INSN_SIZE];

        if (copy_from_kernel_nofault(code, (void *)ip, MCOUNT_INSN_SIZE))
                return -EFAULT;

        if (old_addr != __raw_readl((unsigned long *)code))
                return -EINVAL;

        __raw_writel(new_addr, ip);
        return 0;
}

int ftrace_enable_ftrace_graph_caller(void)
{
        unsigned long ip, old_addr, new_addr;

        ip = (unsigned long)(&ftrace_graph_call) + GRAPH_INSN_OFFSET;
        old_addr = (unsigned long)(&skip_trace);
        new_addr = (unsigned long)(&ftrace_graph_caller);

        return ftrace_mod(ip, old_addr, new_addr);
}

int ftrace_disable_ftrace_graph_caller(void)
{
        unsigned long ip, old_addr, new_addr;

        ip = (unsigned long)(&ftrace_graph_call) + GRAPH_INSN_OFFSET;
        old_addr = (unsigned long)(&ftrace_graph_caller);
        new_addr = (unsigned long)(&skip_trace);

        return ftrace_mod(ip, old_addr, new_addr);
}
#endif /* CONFIG_DYNAMIC_FTRACE */

/*
 * Hook the return address and push it in the stack of return addrs
 * in the current thread info.
 *
 * This is the main routine for the function graph tracer. The function
 * graph tracer essentially works like this:
 *
 * parent is the stack address containing self_addr's return address.
 * We pull the real return address out of parent and store it in
 * current's ret_stack. Then, we replace the return address on the stack
 * with the address of return_to_handler. self_addr is the function that
 * called mcount.
 *
 * When self_addr returns, it will jump to return_to_handler which calls
 * ftrace_return_to_handler. ftrace_return_to_handler will pull the real
 * return address off of current's ret_stack and jump to it.
 */
void prepare_ftrace_return(unsigned long *parent, unsigned long self_addr)
{
        unsigned long old;
        int faulted;
        unsigned long return_hooker = (unsigned long)&return_to_handler;

        if (unlikely(ftrace_graph_is_dead()))
                return;

        if (unlikely(atomic_read(&current->tracing_graph_pause)))
                return;

        /*
         * Protect against fault, even if it shouldn't
         * happen. This tool is too much intrusive to
         * ignore such a protection.
         */
        __asm__ __volatile__(
                "1:                                             \n\t"
                "mov.l          @%2, %0                         \n\t"
                "2:                                             \n\t"
                "mov.l          %3, @%2                         \n\t"
                "mov            #0, %1                          \n\t"
                "3:                                             \n\t"
                ".section .fixup, \"ax\"                        \n\t"
                "4:                                             \n\t"
                "mov.l          5f, %0                          \n\t"
                "jmp            @%0                             \n\t"
                " mov           #1, %1                          \n\t"
                ".balign 4                                      \n\t"
                "5:     .long 3b                                \n\t"
                ".previous                                      \n\t"
                ".section __ex_table,\"a\"                      \n\t"
                ".long 1b, 4b                                   \n\t"
                ".long 2b, 4b                                   \n\t"
                ".previous                                      \n\t"
                : "=&r" (old), "=r" (faulted)
                : "r" (parent), "r" (return_hooker)
        );

        if (unlikely(faulted)) {
                ftrace_graph_stop();
                WARN_ON(1);
                return;
        }

        if (function_graph_enter(old, self_addr, 0, NULL))
                __raw_writel(old, parent);
}
#endif /* CONFIG_FUNCTION_GRAPH_TRACER */