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Linux/arch/s390/kernel/ftrace.c

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  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 #ifdef CC_USING_HOTPATCH
 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 parent, unsigned long ip)
205 {
206         struct ftrace_graph_ent trace;
207 
208         if (unlikely(ftrace_graph_is_dead()))
209                 goto out;
210         if (unlikely(atomic_read(&current->tracing_graph_pause)))
211                 goto out;
212         ip -= MCOUNT_INSN_SIZE;
213         trace.func = ip;
214         trace.depth = current->curr_ret_stack + 1;
215         /* Only trace if the calling function expects to. */
216         if (!ftrace_graph_entry(&trace))
217                 goto out;
218         if (ftrace_push_return_trace(parent, ip, &trace.depth, 0,
219                                      NULL) == -EBUSY)
220                 goto out;
221         parent = (unsigned long) return_to_handler;
222 out:
223         return parent;
224 }
225 NOKPROBE_SYMBOL(prepare_ftrace_return);
226 
227 /*
228  * Patch the kernel code at ftrace_graph_caller location. The instruction
229  * there is branch relative on condition. To enable the ftrace graph code
230  * block, we simply patch the mask field of the instruction to zero and
231  * turn the instruction into a nop.
232  * To disable the ftrace graph code the mask field will be patched to
233  * all ones, which turns the instruction into an unconditional branch.
234  */
235 int ftrace_enable_ftrace_graph_caller(void)
236 {
237         u8 op = 0x04; /* set mask field to zero */
238 
239         s390_kernel_write(__va(ftrace_graph_caller)+1, &op, sizeof(op));
240         return 0;
241 }
242 
243 int ftrace_disable_ftrace_graph_caller(void)
244 {
245         u8 op = 0xf4; /* set mask field to all ones */
246 
247         s390_kernel_write(__va(ftrace_graph_caller)+1, &op, sizeof(op));
248         return 0;
249 }
250 
251 #endif /* CONFIG_FUNCTION_GRAPH_TRACER */
252 

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