arch/s390/kernel/ftrace.c

   1 // SPDX-License-Identifier: GPL-2.0
   2 /*
   3  * Dynamic function tracer architecture backend.
   4  *
   5  * Copyright IBM Corp. 2009,2014
   6  *
   7  *   Author(s): Heiko Carstens <heiko.carstens@de.ibm.com>,
   8  *              Martin Schwidefsky <schwidefsky@de.ibm.com>
   9  */
  10
  11 #include <linux/moduleloader.h>
  12 #include <linux/hardirq.h>
  13 #include <linux/uaccess.h>
  14 #include <linux/ftrace.h>
  15 #include <linux/kernel.h>
  16 #include <linux/types.h>
  17 #include <linux/kprobes.h>
  18 #include <trace/syscall.h>
  19 #include <asm/asm-offsets.h>
  20 #include <asm/cacheflush.h>
  21 #include <asm/set_memory.h>
  22 #include "entry.h"
  23
  24 /*
  25  * The mcount code looks like this:
  26  *      stg     %r14,8(%r15)            # offset 0
  27  *      larl    %r1,<&counter>          # offset 6
  28  *      brasl   %r14,_mcount            # offset 12
  29  *      lg      %r14,8(%r15)            # offset 18
  30  * Total length is 24 bytes. Only the first instruction will be patched
  31  * by ftrace_make_call / ftrace_make_nop.
  32  * The enabled ftrace code block looks like this:
  33  * >    brasl   %r0,ftrace_caller       # offset 0
  34  *      larl    %r1,<&counter>          # offset 6
  35  *      brasl   %r14,_mcount            # offset 12
  36  *      lg      %r14,8(%r15)            # offset 18
  37  * The ftrace function gets called with a non-standard C function call ABI
  38  * where r0 contains the return address. It is also expected that the called
  39  * function only clobbers r0 and r1, but restores r2-r15.
  40  * For module code we can't directly jump to ftrace caller, but need a
  41  * trampoline (ftrace_plt), which clobbers also r1.
  42  * The return point of the ftrace function has offset 24, so execution
  43  * continues behind the mcount block.
  44  * The disabled ftrace code block looks like this:
  45  * >    jg      .+24                    # offset 0
  46  *      larl    %r1,<&counter>          # offset 6
  47  *      brasl   %r14,_mcount            # offset 12
  48  *      lg      %r14,8(%r15)            # offset 18
  49  * The jg instruction branches to offset 24 to skip as many instructions
  50  * as possible.
  51  * In case we use gcc's hotpatch feature the original and also the disabled
  52  * function prologue contains only a single six byte instruction and looks
  53  * like this:
  54  * >    brcl    0,0                     # offset 0
  55  * To enable ftrace the code gets patched like above and afterwards looks
  56  * like this:
  57  * >    brasl   %r0,ftrace_caller       # offset 0
  58  */
  59
  60 unsigned long ftrace_plt;
  61
  62 static inline void ftrace_generate_orig_insn(struct ftrace_insn *insn)
  63 {
  64 #if defined(CC_USING_HOTPATCH) || defined(CC_USING_NOP_MCOUNT)
  65         /* brcl 0,0 */
  66         insn->opc = 0xc004;
  67         insn->disp = 0;
  68 #else
  69         /* stg r14,8(r15) */
  70         insn->opc = 0xe3e0;
  71         insn->disp = 0xf0080024;
  72 #endif
  73 }
  74
  75 static inline void ftrace_generate_kprobe_nop_insn(struct ftrace_insn *insn)
  76 {
  77 #ifdef CONFIG_KPROBES
  78         insn->opc = BREAKPOINT_INSTRUCTION;
  79         insn->disp = KPROBE_ON_FTRACE_NOP;
  80 #endif
  81 }
  82
  83 static inline void ftrace_generate_kprobe_call_insn(struct ftrace_insn *insn)
  84 {
  85 #ifdef CONFIG_KPROBES
  86         insn->opc = BREAKPOINT_INSTRUCTION;
  87         insn->disp = KPROBE_ON_FTRACE_CALL;
  88 #endif
  89 }
  90
  91 int ftrace_modify_call(struct dyn_ftrace *rec, unsigned long old_addr,
  92                        unsigned long addr)
  93 {
  94         return 0;
  95 }
  96
  97 int ftrace_make_nop(struct module *mod, struct dyn_ftrace *rec,
  98                     unsigned long addr)
  99 {
 100         struct ftrace_insn orig, new, old;
 101
 102         if (probe_kernel_read(&old, (void *) rec->ip, sizeof(old)))
 103                 return -EFAULT;
 104         if (addr == MCOUNT_ADDR) {
 105                 /* Initial code replacement */
 106                 ftrace_generate_orig_insn(&orig);
 107                 ftrace_generate_nop_insn(&new);
 108         } else {
 109                 /* Replace ftrace call with a nop. */
 110                 ftrace_generate_call_insn(&orig, rec->ip);
 111                 ftrace_generate_nop_insn(&new);
 112         }
 113         /* Verify that the to be replaced code matches what we expect. */
 114         if (memcmp(&orig, &old, sizeof(old)))
 115                 return -EINVAL;
 116         s390_kernel_write((void *) rec->ip, &new, sizeof(new));
 117         return 0;
 118 }
 119
 120 int ftrace_make_call(struct dyn_ftrace *rec, unsigned long addr)
 121 {
 122         struct ftrace_insn orig, new, old;
 123
 124         if (probe_kernel_read(&old, (void *) rec->ip, sizeof(old)))
 125                 return -EFAULT;
 126         /* Replace nop with an ftrace call. */
 127         ftrace_generate_nop_insn(&orig);
 128         ftrace_generate_call_insn(&new, rec->ip);
 129
 130         /* Verify that the to be replaced code matches what we expect. */
 131         if (memcmp(&orig, &old, sizeof(old)))
 132                 return -EINVAL;
 133         s390_kernel_write((void *) rec->ip, &new, sizeof(new));
 134         return 0;
 135 }
 136
 137 int ftrace_update_ftrace_func(ftrace_func_t func)
 138 {
 139         return 0;
 140 }
 141
 142 int __init ftrace_dyn_arch_init(void)
 143 {
 144         return 0;
 145 }
 146
 147 #ifdef CONFIG_MODULES
 148
 149 static int __init ftrace_plt_init(void)
 150 {
 151         unsigned int *ip;
 152
 153         ftrace_plt = (unsigned long) module_alloc(PAGE_SIZE);
 154         if (!ftrace_plt)
 155                 panic("cannot allocate ftrace plt\n");
 156         ip = (unsigned int *) ftrace_plt;
 157         ip[0] = 0x0d10e310; /* basr 1,0; lg 1,10(1); br 1 */
 158         ip[1] = 0x100a0004;
 159         ip[2] = 0x07f10000;
 160         ip[3] = FTRACE_ADDR >> 32;
 161         ip[4] = FTRACE_ADDR & 0xffffffff;
 162         set_memory_ro(ftrace_plt, 1);
 163         return 0;
 164 }
 165 device_initcall(ftrace_plt_init);
 166
 167 #endif /* CONFIG_MODULES */
 168
 169 #ifdef CONFIG_FUNCTION_GRAPH_TRACER
 170 /*
 171  * Hook the return address and push it in the stack of return addresses
 172  * in current thread info.
 173  */
 174 unsigned long prepare_ftrace_return(unsigned long ra, unsigned long sp,
 175                                     unsigned long ip)
 176 {
 177         if (unlikely(ftrace_graph_is_dead()))
 178                 goto out;
 179         if (unlikely(atomic_read(&current->tracing_graph_pause)))
 180                 goto out;
 181         ip -= MCOUNT_INSN_SIZE;
 182         if (!function_graph_enter(ra, ip, 0, (void *) sp))
 183                 ra = (unsigned long) return_to_handler;
 184 out:
 185         return ra;
 186 }
 187 NOKPROBE_SYMBOL(prepare_ftrace_return);
 188
 189 /*
 190  * Patch the kernel code at ftrace_graph_caller location. The instruction
 191  * there is branch relative on condition. To enable the ftrace graph code
 192  * block, we simply patch the mask field of the instruction to zero and
 193  * turn the instruction into a nop.
 194  * To disable the ftrace graph code the mask field will be patched to
 195  * all ones, which turns the instruction into an unconditional branch.
 196  */
 197 int ftrace_enable_ftrace_graph_caller(void)
 198 {
 199         u8 op = 0x04; /* set mask field to zero */
 200
 201         s390_kernel_write(__va(ftrace_graph_caller)+1, &op, sizeof(op));
 202         return 0;
 203 }
 204
 205 int ftrace_disable_ftrace_graph_caller(void)
 206 {
 207         u8 op = 0xf4; /* set mask field to all ones */
 208
 209         s390_kernel_write(__va(ftrace_graph_caller)+1, &op, sizeof(op));
 210         return 0;
 211 }
 212
 213 #endif /* CONFIG_FUNCTION_GRAPH_TRACER */
 214
 215 #ifdef CONFIG_KPROBES_ON_FTRACE
 216 void kprobe_ftrace_handler(unsigned long ip, unsigned long parent_ip,
 217                 struct ftrace_ops *ops, struct pt_regs *regs)
 218 {
 219         struct kprobe_ctlblk *kcb;
 220         struct kprobe *p = get_kprobe((kprobe_opcode_t *)ip);
 221
 222         if (unlikely(!p) || kprobe_disabled(p))
 223                 return;
 224
 225         if (kprobe_running()) {
 226                 kprobes_inc_nmissed_count(p);
 227                 return;
 228         }
 229
 230         __this_cpu_write(current_kprobe, p);
 231
 232         kcb = get_kprobe_ctlblk();
 233         kcb->kprobe_status = KPROBE_HIT_ACTIVE;
 234
 235         instruction_pointer_set(regs, ip);
 236
 237         if (!p->pre_handler || !p->pre_handler(p, regs)) {
 238
 239                 instruction_pointer_set(regs, ip + MCOUNT_INSN_SIZE);
 240
 241                 if (unlikely(p->post_handler)) {
 242                         kcb->kprobe_status = KPROBE_HIT_SSDONE;
 243                         p->post_handler(p, regs, 0);
 244                 }
 245         }
 246         __this_cpu_write(current_kprobe, NULL);
 247 }
 248 NOKPROBE_SYMBOL(kprobe_ftrace_handler);
 249
 250 int arch_prepare_kprobe_ftrace(struct kprobe *p)
 251 {
 252         p->ainsn.insn = NULL;
 253         return 0;
 254 }
 255 #endif