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

#include <linux/hardirq.h>
#include <linux/uaccess.h>
#include <linux/ftrace.h>
#include <linux/kernel.h>
#include <linux/types.h>
#include <linux/kmsan-checks.h>
#include <linux/cpufeature.h>
#include <linux/kprobes.h>
#include <linux/execmem.h>
#include <trace/syscall.h>
#include <asm/asm-offsets.h>
#include <asm/text-patching.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;

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_exrl;
                tend = ftrace_shared_hotpatch_trampoline_exrl_end;
        }
#endif /* CONFIG_EXPOLINE */
        if (end)
                *end = tend;
        return tstart;
}

bool ftrace_need_init_nop(void)
{
        return !cpu_has_seq_insn();
}

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 struct ftrace_insn orig = { .opc = 0xc004, .disp = 0 };
        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;
        struct ftrace_insn old;
        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;
        }
#endif

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

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

static struct ftrace_hotpatch_trampoline *ftrace_get_trampoline(struct dyn_ftrace *rec)
{
        struct ftrace_hotpatch_trampoline *trampoline;
        struct ftrace_insn insn;
        s64 disp;
        u16 opc;

        if (copy_from_kernel_nofault(&insn, (void *)rec->ip, sizeof(insn)))
                return ERR_PTR(-EFAULT);
        disp = (s64)insn.disp * 2;
        trampoline = (void *)(rec->ip + disp);
        if (get_kernel_nofault(opc, &trampoline->brasl_opc))
                return ERR_PTR(-EFAULT);
        if (opc != 0xc015)
                return ERR_PTR(-EINVAL);
        return trampoline;
}

static inline struct ftrace_insn
ftrace_generate_branch_insn(unsigned long ip, unsigned long target)
{
        /* brasl r0,target or brcl 0,0 */
        return (struct ftrace_insn){ .opc = target ? 0xc005 : 0xc004,
                                     .disp = target ? (target - ip) / 2 : 0 };
}

static int ftrace_patch_branch_insn(unsigned long ip, unsigned long old_target,
                                    unsigned long target)
{
        struct ftrace_insn orig = ftrace_generate_branch_insn(ip, old_target);
        struct ftrace_insn new = ftrace_generate_branch_insn(ip, target);
        struct ftrace_insn old;

        if (!IS_ALIGNED(ip, 8))
                return -EINVAL;
        if (copy_from_kernel_nofault(&old, (void *)ip, sizeof(old)))
                return -EFAULT;
        /* Verify that the to be replaced code matches what we expect. */
        if (memcmp(&orig, &old, sizeof(old)))
                return -EINVAL;
        s390_kernel_write((void *)ip, &new, sizeof(new));
        return 0;
}

static int ftrace_modify_trampoline_call(struct dyn_ftrace *rec,
                                         unsigned long old_addr,
                                         unsigned long addr)
{
        struct ftrace_hotpatch_trampoline *trampoline;
        u64 old;

        trampoline = ftrace_get_trampoline(rec);
        if (IS_ERR(trampoline))
                return PTR_ERR(trampoline);
        if (get_kernel_nofault(old, &trampoline->interceptor))
                return -EFAULT;
        if (old != old_addr)
                return -EINVAL;
        s390_kernel_write(&trampoline->interceptor, &addr, sizeof(addr));
        return 0;
}

int ftrace_modify_call(struct dyn_ftrace *rec, unsigned long old_addr,
                       unsigned long addr)
{
        if (cpu_has_seq_insn())
                return ftrace_patch_branch_insn(rec->ip, old_addr, addr);
        else
                return ftrace_modify_trampoline_call(rec, old_addr, addr);
}

static int ftrace_patch_branch_mask(void *addr, u16 expected, bool enable)
{
        u16 old;
        u8 op;

        if (get_kernel_nofault(old, addr))
                return -EFAULT;
        if (old != expected)
                return -EINVAL;
        /* set mask field to all ones or zeroes */
        op = enable ? 0xf4 : 0x04;
        s390_kernel_write((char *)addr + 1, &op, sizeof(op));
        return 0;
}

int ftrace_make_nop(struct module *mod, struct dyn_ftrace *rec,
                    unsigned long addr)
{
        /* Expect brcl 0xf,... for the !cpu_has_seq_insn() case */
        if (cpu_has_seq_insn())
                return ftrace_patch_branch_insn(rec->ip, addr, 0);
        else
                return ftrace_patch_branch_mask((void *)rec->ip, 0xc0f4, false);
}

static int ftrace_make_trampoline_call(struct dyn_ftrace *rec, unsigned long addr)
{
        struct ftrace_hotpatch_trampoline *trampoline;

        trampoline = ftrace_get_trampoline(rec);
        if (IS_ERR(trampoline))
                return PTR_ERR(trampoline);
        s390_kernel_write(&trampoline->interceptor, &addr, sizeof(addr));
        /* Expect brcl 0x0,... */
        return ftrace_patch_branch_mask((void *)rec->ip, 0xc004, true);
}

int ftrace_make_call(struct dyn_ftrace *rec, unsigned long addr)
{
        if (cpu_has_seq_insn())
                return ftrace_patch_branch_insn(rec->ip, 0, addr);
        else
                return ftrace_make_trampoline_call(rec, addr);
}

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

void arch_ftrace_update_code(int command)
{
        ftrace_modify_all_code(command);
}

void ftrace_arch_code_modify_post_process(void)
{
        /*
         * Flush any pre-fetched instructions on all
         * CPUs to make the new code visible.
         */
        text_poke_sync_lock();
}

#ifdef CONFIG_FUNCTION_GRAPH_TRACER

void ftrace_graph_func(unsigned long ip, unsigned long parent_ip,
                       struct ftrace_ops *op, struct ftrace_regs *fregs)
{
        unsigned long *parent = &arch_ftrace_regs(fregs)->regs.gprs[14];
        unsigned long sp = arch_ftrace_regs(fregs)->regs.gprs[15];

        if (unlikely(ftrace_graph_is_dead()))
                return;
        if (unlikely(atomic_read(&current->tracing_graph_pause)))
                return;
        if (!function_graph_enter_regs(*parent, ip, 0, (unsigned long *)sp, fregs))
                *parent = (unsigned long)&return_to_handler;
}

#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;

        if (unlikely(kprobe_ftrace_disabled))
                return;

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

        kmsan_unpoison_memory(fregs, ftrace_regs_size());
        regs = ftrace_get_regs(fregs);
        p = get_kprobe((kprobe_opcode_t *)ip);
        if (!regs || 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:
        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