root/arch/s390/kernel/ftrace.c

DEFINITIONS

1. ftrace_generate_orig_insn
2. is_kprobe_on_ftrace
3. ftrace_generate_kprobe_nop_insn
4. ftrace_generate_kprobe_call_insn
5. ftrace_modify_call
6. ftrace_make_nop
7. ftrace_make_call
8. ftrace_update_ftrace_func
9. ftrace_dyn_arch_init
10. ftrace_plt_init
11. prepare_ftrace_return
12. ftrace_enable_ftrace_graph_caller
13. ftrace_disable_ftrace_graph_caller

   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 int is_kprobe_on_ftrace(struct ftrace_insn *insn)
  76 {
  77 #ifdef CONFIG_KPROBES
  78         if (insn->opc == BREAKPOINT_INSTRUCTION)
  79                 return 1;
  80 #endif
  81         return 0;
  82 }
  83 
  84 static inline void ftrace_generate_kprobe_nop_insn(struct ftrace_insn *insn)
  85 {
  86 #ifdef CONFIG_KPROBES
  87         insn->opc = BREAKPOINT_INSTRUCTION;
  88         insn->disp = KPROBE_ON_FTRACE_NOP;
  89 #endif
  90 }
  91 
  92 static inline void ftrace_generate_kprobe_call_insn(struct ftrace_insn *insn)
  93 {
  94 #ifdef CONFIG_KPROBES
  95         insn->opc = BREAKPOINT_INSTRUCTION;
  96         insn->disp = KPROBE_ON_FTRACE_CALL;
  97 #endif
  98 }
  99 
 100 int ftrace_modify_call(struct dyn_ftrace *rec, unsigned long old_addr,
 101                        unsigned long addr)
 102 {
 103         return 0;
 104 }
 105 
 106 int ftrace_make_nop(struct module *mod, struct dyn_ftrace *rec,
 107                     unsigned long addr)
 108 {
 109         struct ftrace_insn orig, new, old;
 110 
 111         if (probe_kernel_read(&old, (void *) rec->ip, sizeof(old)))
 112                 return -EFAULT;
 113         if (addr == MCOUNT_ADDR) {
 114                 /* Initial code replacement */
 115                 ftrace_generate_orig_insn(&orig);
 116                 ftrace_generate_nop_insn(&new);
 117         } else if (is_kprobe_on_ftrace(&old)) {
 118                 /*
 119                  * If we find a breakpoint instruction, a kprobe has been
 120                  * placed at the beginning of the function. We write the
 121                  * constant KPROBE_ON_FTRACE_NOP into the remaining four
 122                  * bytes of the original instruction so that the kprobes
 123                  * handler can execute a nop, if it reaches this breakpoint.
 124                  */
 125                 ftrace_generate_kprobe_call_insn(&orig);
 126                 ftrace_generate_kprobe_nop_insn(&new);
 127         } else {
 128                 /* Replace ftrace call with a nop. */
 129                 ftrace_generate_call_insn(&orig, rec->ip);
 130                 ftrace_generate_nop_insn(&new);
 131         }
 132         /* Verify that the to be replaced code matches what we expect. */
 133         if (memcmp(&orig, &old, sizeof(old)))
 134                 return -EINVAL;
 135         s390_kernel_write((void *) rec->ip, &new, sizeof(new));
 136         return 0;
 137 }
 138 
 139 int ftrace_make_call(struct dyn_ftrace *rec, unsigned long addr)
 140 {
 141         struct ftrace_insn orig, new, old;
 142 
 143         if (probe_kernel_read(&old, (void *) rec->ip, sizeof(old)))
 144                 return -EFAULT;
 145         if (is_kprobe_on_ftrace(&old)) {
 146                 /*
 147                  * If we find a breakpoint instruction, a kprobe has been
 148                  * placed at the beginning of the function. We write the
 149                  * constant KPROBE_ON_FTRACE_CALL into the remaining four
 150                  * bytes of the original instruction so that the kprobes
 151                  * handler can execute a brasl if it reaches this breakpoint.
 152                  */
 153                 ftrace_generate_kprobe_nop_insn(&orig);
 154                 ftrace_generate_kprobe_call_insn(&new);
 155         } else {
 156                 /* Replace nop with an ftrace call. */
 157                 ftrace_generate_nop_insn(&orig);
 158                 ftrace_generate_call_insn(&new, rec->ip);
 159         }
 160         /* Verify that the to be replaced code matches what we expect. */
 161         if (memcmp(&orig, &old, sizeof(old)))
 162                 return -EINVAL;
 163         s390_kernel_write((void *) rec->ip, &new, sizeof(new));
 164         return 0;
 165 }
 166 
 167 int ftrace_update_ftrace_func(ftrace_func_t func)
 168 {
 169         return 0;
 170 }
 171 
 172 int __init ftrace_dyn_arch_init(void)
 173 {
 174         return 0;
 175 }
 176 
 177 #ifdef CONFIG_MODULES
 178 
 179 static int __init ftrace_plt_init(void)
 180 {
 181         unsigned int *ip;
 182 
 183         ftrace_plt = (unsigned long) module_alloc(PAGE_SIZE);
 184         if (!ftrace_plt)
 185                 panic("cannot allocate ftrace plt\n");
 186         ip = (unsigned int *) ftrace_plt;
 187         ip[0] = 0x0d10e310; /* basr 1,0; lg 1,10(1); br 1 */
 188         ip[1] = 0x100a0004;
 189         ip[2] = 0x07f10000;
 190         ip[3] = FTRACE_ADDR >> 32;
 191         ip[4] = FTRACE_ADDR & 0xffffffff;
 192         set_memory_ro(ftrace_plt, 1);
 193         return 0;
 194 }
 195 device_initcall(ftrace_plt_init);
 196 
 197 #endif /* CONFIG_MODULES */
 198 
 199 #ifdef CONFIG_FUNCTION_GRAPH_TRACER
 200 /*
 201  * Hook the return address and push it in the stack of return addresses
 202  * in current thread info.
 203  */
 204 unsigned long prepare_ftrace_return(unsigned long ra, unsigned long sp,
 205                                     unsigned long ip)
 206 {
 207         if (unlikely(ftrace_graph_is_dead()))
 208                 goto out;
 209         if (unlikely(atomic_read(&current->tracing_graph_pause)))
 210                 goto out;
 211         ip -= MCOUNT_INSN_SIZE;
 212         if (!function_graph_enter(ra, ip, 0, (void *) sp))
 213                 ra = (unsigned long) return_to_handler;
 214 out:
 215         return ra;
 216 }
 217 NOKPROBE_SYMBOL(prepare_ftrace_return);
 218 
 219 /*
 220  * Patch the kernel code at ftrace_graph_caller location. The instruction
 221  * there is branch relative on condition. To enable the ftrace graph code
 222  * block, we simply patch the mask field of the instruction to zero and
 223  * turn the instruction into a nop.
 224  * To disable the ftrace graph code the mask field will be patched to
 225  * all ones, which turns the instruction into an unconditional branch.
 226  */
 227 int ftrace_enable_ftrace_graph_caller(void)
 228 {
 229         u8 op = 0x04; /* set mask field to zero */
 230 
 231         s390_kernel_write(__va(ftrace_graph_caller)+1, &op, sizeof(op));
 232         return 0;
 233 }
 234 
 235 int ftrace_disable_ftrace_graph_caller(void)
 236 {
 237         u8 op = 0xf4; /* set mask field to all ones */
 238 
 239         s390_kernel_write(__va(ftrace_graph_caller)+1, &op, sizeof(op));
 240         return 0;
 241 }
 242 
 243 #endif /* CONFIG_FUNCTION_GRAPH_TRACER */