// SPDX-License-Identifier: GPL-2.0
/*
 * Dynamic function tracer architecture backend.
 *
 * Copyright IBM Corp. 2009,2014
 *
 *   Author(s): Heiko Carstens <heiko.carstens@de.ibm.com>,
 *              Martin Schwidefsky <schwidefsky@de.ibm.com>
 */

#include <linux/moduleloader.h>
#include <linux/hardirq.h>
#include <linux/uaccess.h>
#include <linux/ftrace.h>
#include <linux/kernel.h>
#include <linux/types.h>
#include <linux/kprobes.h>
#include <trace/syscall.h>
#include <asm/asm-offsets.h>
#include <asm/cacheflush.h>
#include <asm/ftrace.lds.h>
#include <asm/nospec-branch.h>
#include <asm/set_memory.h>
#include "entry.h"
#include "ftrace.h"

/*
 * To generate function prologue either gcc's hotpatch feature (since gcc 4.8)
 * or a combination of -pg -mrecord-mcount -mnop-mcount -mfentry flags
 * (since gcc 9 / clang 10) is used.
 * In both cases the original and also the disabled function prologue contains
 * only a single six byte instruction and looks like this:
 * >    brcl    0,0                     # offset 0
 * To enable ftrace the code gets patched like above and afterwards looks
 * like this:
 * >    brasl   %r0,ftrace_caller       # offset 0
 *
 * The instruction will be patched by ftrace_make_call / ftrace_make_nop.
 * The ftrace function gets called with a non-standard C function call ABI
 * where r0 contains the return address. It is also expected that the called
 * function only clobbers r0 and r1, but restores r2-r15.
 * For module code we can't directly jump to ftrace caller, but need a
 * trampoline (ftrace_plt), which clobbers also r1.
 */

void *ftrace_func __read_mostly = ftrace_stub;
struct ftrace_insn {
        u16 opc;
        s32 disp;
} __packed;

asm(
        "       .align 16\n"
        "ftrace_shared_hotpatch_trampoline_br:\n"
        "       lmg     %r0,%r1,2(%r1)\n"
        "       br      %r1\n"
        "ftrace_shared_hotpatch_trampoline_br_end:\n"
);

#ifdef CONFIG_EXPOLINE
asm(
        "       .align 16\n"
        "ftrace_shared_hotpatch_trampoline_ex:\n"
        "       lmg     %r0,%r1,2(%r1)\n"
        "       ex      %r0," __stringify(__LC_BR_R1) "(%r0)\n"
        "       j       .\n"
        "ftrace_shared_hotpatch_trampoline_ex_end:\n"
);

asm(
        "       .align 16\n"
        "ftrace_shared_hotpatch_trampoline_exrl:\n"
        "       lmg     %r0,%r1,2(%r1)\n"
        "       .insn   ril,0xc60000000000,%r0,0f\n" /* exrl */
        "       j       .\n"
        "0:     br      %r1\n"
        "ftrace_shared_hotpatch_trampoline_exrl_end:\n"
);
#endif /* CONFIG_EXPOLINE */

#ifdef CONFIG_MODULES
static char *ftrace_plt;

asm(
        "       .data\n"
        "ftrace_plt_template:\n"
        "       basr    %r1,%r0\n"
        "       lg      %r1,0f-.(%r1)\n"
        "       br      %r1\n"
        "0:     .quad   ftrace_caller\n"
        "ftrace_plt_template_end:\n"
        "       .previous\n"
);
#endif /* CONFIG_MODULES */

static const char *ftrace_shared_hotpatch_trampoline(const char **end)
{
        const char *tstart, *tend;

        tstart = ftrace_shared_hotpatch_trampoline_br;
        tend = ftrace_shared_hotpatch_trampoline_br_end;
#ifdef CONFIG_EXPOLINE
        if (!nospec_disable) {
                tstart = ftrace_shared_hotpatch_trampoline_ex;
                tend = ftrace_shared_hotpatch_trampoline_ex_end;
                if (test_facility(35)) { /* exrl */
                        tstart = ftrace_shared_hotpatch_trampoline_exrl;
                        tend = ftrace_shared_hotpatch_trampoline_exrl_end;
                }
        }
#endif /* CONFIG_EXPOLINE */
        if (end)
                *end = tend;
        return tstart;
}

bool ftrace_need_init_nop(void)
{
        return ftrace_shared_hotpatch_trampoline(NULL);
}

int ftrace_init_nop(struct module *mod, struct dyn_ftrace *rec)
{
        static struct ftrace_hotpatch_trampoline *next_vmlinux_trampoline =
                __ftrace_hotpatch_trampolines_start;
        static const char orig[6] = { 0xc0, 0x04, 0x00, 0x00, 0x00, 0x00 };
        static struct ftrace_hotpatch_trampoline *trampoline;
        struct ftrace_hotpatch_trampoline **next_trampoline;
        struct ftrace_hotpatch_trampoline *trampolines_end;
        struct ftrace_hotpatch_trampoline tmp;
        struct ftrace_insn *insn;
        const char *shared;
        s32 disp;

        BUILD_BUG_ON(sizeof(struct ftrace_hotpatch_trampoline) !=
                     SIZEOF_FTRACE_HOTPATCH_TRAMPOLINE);

        next_trampoline = &next_vmlinux_trampoline;
        trampolines_end = __ftrace_hotpatch_trampolines_end;
        shared = ftrace_shared_hotpatch_trampoline(NULL);
#ifdef CONFIG_MODULES
        if (mod) {
                next_trampoline = &mod->arch.next_trampoline;
                trampolines_end = mod->arch.trampolines_end;
                shared = ftrace_plt;
        }
#endif

        if (WARN_ON_ONCE(*next_trampoline >= trampolines_end))
                return -ENOMEM;
        trampoline = (*next_trampoline)++;

        /* Check for the compiler-generated fentry nop (brcl 0, .). */
        if (WARN_ON_ONCE(memcmp((const void *)rec->ip, &orig, sizeof(orig))))
                return -EINVAL;

        /* Generate the trampoline. */
        tmp.brasl_opc = 0xc015; /* brasl %r1, shared */
        tmp.brasl_disp = (shared - (const char *)&trampoline->brasl_opc) / 2;
        tmp.interceptor = FTRACE_ADDR;
        tmp.rest_of_intercepted_function = rec->ip + sizeof(struct ftrace_insn);
        s390_kernel_write(trampoline, &tmp, sizeof(tmp));

        /* Generate a jump to the trampoline. */
        disp = ((char *)trampoline - (char *)rec->ip) / 2;
        insn = (struct ftrace_insn *)rec->ip;
        s390_kernel_write(&insn->disp, &disp, sizeof(disp));

        return 0;
}

int ftrace_modify_call(struct dyn_ftrace *rec, unsigned long old_addr,
                       unsigned long addr)
{
        return 0;
}

static void ftrace_generate_nop_insn(struct ftrace_insn *insn)
{
        /* brcl 0,0 */
        insn->opc = 0xc004;
        insn->disp = 0;
}

static void ftrace_generate_call_insn(struct ftrace_insn *insn,
                                      unsigned long ip)
{
        unsigned long target;

        /* brasl r0,ftrace_caller */
        target = FTRACE_ADDR;
#ifdef CONFIG_MODULES
        if (is_module_addr((void *)ip))
                target = (unsigned long)ftrace_plt;
#endif /* CONFIG_MODULES */
        insn->opc = 0xc005;
        insn->disp = (target - ip) / 2;
}

static void brcl_disable(void *brcl)
{
        u8 op = 0x04; /* set mask field to zero */

        s390_kernel_write((char *)brcl + 1, &op, sizeof(op));
}

int ftrace_make_nop(struct module *mod, struct dyn_ftrace *rec,
                    unsigned long addr)
{
        struct ftrace_insn orig, new, old;

        if (ftrace_shared_hotpatch_trampoline(NULL)) {
                brcl_disable((void *)rec->ip);
                return 0;
        }

        if (copy_from_kernel_nofault(&old, (void *) rec->ip, sizeof(old)))
                return -EFAULT;
        /* Replace ftrace call with a nop. */
        ftrace_generate_call_insn(&orig, rec->ip);
        ftrace_generate_nop_insn(&new);

        /* Verify that the to be replaced code matches what we expect. */
        if (memcmp(&orig, &old, sizeof(old)))
                return -EINVAL;
        s390_kernel_write((void *) rec->ip, &new, sizeof(new));
        return 0;
}

static void brcl_enable(void *brcl)
{
        u8 op = 0xf4; /* set mask field to all ones */

        s390_kernel_write((char *)brcl + 1, &op, sizeof(op));
}

int ftrace_make_call(struct dyn_ftrace *rec, unsigned long addr)
{
        struct ftrace_insn orig, new, old;

        if (ftrace_shared_hotpatch_trampoline(NULL)) {
                brcl_enable((void *)rec->ip);
                return 0;
        }

        if (copy_from_kernel_nofault(&old, (void *) rec->ip, sizeof(old)))
                return -EFAULT;
        /* Replace nop with an ftrace call. */
        ftrace_generate_nop_insn(&orig);
        ftrace_generate_call_insn(&new, rec->ip);

        /* Verify that the to be replaced code matches what we expect. */
        if (memcmp(&orig, &old, sizeof(old)))
                return -EINVAL;
        s390_kernel_write((void *) rec->ip, &new, sizeof(new));
        return 0;
}

int ftrace_update_ftrace_func(ftrace_func_t func)
{
        ftrace_func = func;
        return 0;
}

int __init ftrace_dyn_arch_init(void)
{
        return 0;
}

void arch_ftrace_update_code(int command)
{
        if (ftrace_shared_hotpatch_trampoline(NULL))
                ftrace_modify_all_code(command);
        else
                ftrace_run_stop_machine(command);
}

static void __ftrace_sync(void *dummy)
{
}

int ftrace_arch_code_modify_post_process(void)
{
        if (ftrace_shared_hotpatch_trampoline(NULL)) {
                /* Send SIGP to the other CPUs, so they see the new code. */
                smp_call_function(__ftrace_sync, NULL, 1);
        }
        return 0;
}

#ifdef CONFIG_MODULES

static int __init ftrace_plt_init(void)
{
        const char *start, *end;

        ftrace_plt = module_alloc(PAGE_SIZE);
        if (!ftrace_plt)
                panic("cannot allocate ftrace plt\n");

        start = ftrace_shared_hotpatch_trampoline(&end);
        if (!start) {
                start = ftrace_plt_template;
                end = ftrace_plt_template_end;
        }
        memcpy(ftrace_plt, start, end - start);
        set_memory_ro((unsigned long)ftrace_plt, 1);
        return 0;
}
device_initcall(ftrace_plt_init);

#endif /* CONFIG_MODULES */

#ifdef CONFIG_FUNCTION_GRAPH_TRACER
/*
 * Hook the return address and push it in the stack of return addresses
 * in current thread info.
 */
unsigned long prepare_ftrace_return(unsigned long ra, unsigned long sp,
                                    unsigned long ip)
{
        if (unlikely(ftrace_graph_is_dead()))
                goto out;
        if (unlikely(atomic_read(&current->tracing_graph_pause)))
                goto out;
        ip -= MCOUNT_INSN_SIZE;
        if (!function_graph_enter(ra, ip, 0, (void *) sp))
                ra = (unsigned long) return_to_handler;
out:
        return ra;
}
NOKPROBE_SYMBOL(prepare_ftrace_return);

/*
 * Patch the kernel code at ftrace_graph_caller location. The instruction
 * there is branch relative on condition. To enable the ftrace graph code
 * block, we simply patch the mask field of the instruction to zero and
 * turn the instruction into a nop.
 * To disable the ftrace graph code the mask field will be patched to
 * all ones, which turns the instruction into an unconditional branch.
 */
int ftrace_enable_ftrace_graph_caller(void)
{
        brcl_disable(ftrace_graph_caller);
        return 0;
}

int ftrace_disable_ftrace_graph_caller(void)
{
        brcl_enable(ftrace_graph_caller);
        return 0;
}

#endif /* CONFIG_FUNCTION_GRAPH_TRACER */

#ifdef CONFIG_KPROBES_ON_FTRACE
void kprobe_ftrace_handler(unsigned long ip, unsigned long parent_ip,
                struct ftrace_ops *ops, struct ftrace_regs *fregs)
{
        struct kprobe_ctlblk *kcb;
        struct pt_regs *regs;
        struct kprobe *p;
        int bit;

        bit = ftrace_test_recursion_trylock(ip, parent_ip);
        if (bit < 0)
                return;

        regs = ftrace_get_regs(fregs);
        preempt_disable_notrace();
        p = get_kprobe((kprobe_opcode_t *)ip);
        if (unlikely(!p) || kprobe_disabled(p))
                goto out;

        if (kprobe_running()) {
                kprobes_inc_nmissed_count(p);
                goto out;
        }

        __this_cpu_write(current_kprobe, p);

        kcb = get_kprobe_ctlblk();
        kcb->kprobe_status = KPROBE_HIT_ACTIVE;

        instruction_pointer_set(regs, ip);

        if (!p->pre_handler || !p->pre_handler(p, regs)) {

                instruction_pointer_set(regs, ip + MCOUNT_INSN_SIZE);

                if (unlikely(p->post_handler)) {
                        kcb->kprobe_status = KPROBE_HIT_SSDONE;
                        p->post_handler(p, regs, 0);
                }
        }
        __this_cpu_write(current_kprobe, NULL);
out:
        preempt_enable_notrace();
        ftrace_test_recursion_unlock(bit);
}
NOKPROBE_SYMBOL(kprobe_ftrace_handler);

int arch_prepare_kprobe_ftrace(struct kprobe *p)
{
        p->ainsn.insn = NULL;
        return 0;
}
#endif