Commit 08d636b6 authored by Steven Rostedt's avatar Steven Rostedt Committed by Steven Rostedt
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ftrace/x86: Have arch x86_64 use breakpoints instead of stop machine



This method changes x86 to add a breakpoint to the mcount locations
instead of calling stop machine.

Now that iret can be handled by NMIs, we perform the following to
update code:

1) Add a breakpoint to all locations that will be modified

2) Sync all cores

3) Update all locations to be either a nop or call (except breakpoint
   op)

4) Sync all cores

5) Remove the breakpoint with the new code.

6) Sync all cores

[
  Added updates that Masami suggested:
   Use unlikely(modifying_ftrace_code) in int3 trap to keep kprobes efficient.
   Don't use NOTIFY_* in ftrace handler in int3 as it is not a notifier.
]

Cc: H. Peter Anvin <hpa@zytor.com>
Acked-by: default avatarMasami Hiramatsu <masami.hiramatsu.pt@hitachi.com>
Signed-off-by: default avatarSteven Rostedt <rostedt@goodmis.org>
parent 438ced17
......@@ -34,6 +34,7 @@
#ifndef __ASSEMBLY__
extern void mcount(void);
extern int modifying_ftrace_code;
static inline unsigned long ftrace_call_adjust(unsigned long addr)
{
......@@ -50,6 +51,8 @@ struct dyn_arch_ftrace {
/* No extra data needed for x86 */
};
int ftrace_int3_handler(struct pt_regs *regs);
#endif /* CONFIG_DYNAMIC_FTRACE */
#endif /* __ASSEMBLY__ */
#endif /* CONFIG_FUNCTION_TRACER */
......
......@@ -20,6 +20,7 @@
#include <linux/init.h>
#include <linux/list.h>
#include <linux/module.h>
#include <linux/kprobes.h>
#include <trace/syscall.h>
......@@ -334,6 +335,347 @@ int ftrace_update_ftrace_func(ftrace_func_t func)
return ret;
}
int modifying_ftrace_code __read_mostly;
/*
* A breakpoint was added to the code address we are about to
* modify, and this is the handle that will just skip over it.
* We are either changing a nop into a trace call, or a trace
* call to a nop. While the change is taking place, we treat
* it just like it was a nop.
*/
int ftrace_int3_handler(struct pt_regs *regs)
{
if (WARN_ON_ONCE(!regs))
return 0;
if (!ftrace_location(regs->ip - 1))
return 0;
regs->ip += MCOUNT_INSN_SIZE - 1;
return 1;
}
static int ftrace_write(unsigned long ip, const char *val, int size)
{
/*
* On x86_64, kernel text mappings are mapped read-only with
* CONFIG_DEBUG_RODATA. So we use the kernel identity mapping instead
* of the kernel text mapping to modify the kernel text.
*
* For 32bit kernels, these mappings are same and we can use
* kernel identity mapping to modify code.
*/
if (within(ip, (unsigned long)_text, (unsigned long)_etext))
ip = (unsigned long)__va(__pa(ip));
return probe_kernel_write((void *)ip, val, size);
}
static int add_break(unsigned long ip, const char *old)
{
unsigned char replaced[MCOUNT_INSN_SIZE];
unsigned char brk = BREAKPOINT_INSTRUCTION;
if (probe_kernel_read(replaced, (void *)ip, MCOUNT_INSN_SIZE))
return -EFAULT;
/* Make sure it is what we expect it to be */
if (memcmp(replaced, old, MCOUNT_INSN_SIZE) != 0)
return -EINVAL;
if (ftrace_write(ip, &brk, 1))
return -EPERM;
return 0;
}
static int add_brk_on_call(struct dyn_ftrace *rec, unsigned long addr)
{
unsigned const char *old;
unsigned long ip = rec->ip;
old = ftrace_call_replace(ip, addr);
return add_break(rec->ip, old);
}
static int add_brk_on_nop(struct dyn_ftrace *rec)
{
unsigned const char *old;
old = ftrace_nop_replace();
return add_break(rec->ip, old);
}
static int add_breakpoints(struct dyn_ftrace *rec, int enable)
{
unsigned long ftrace_addr;
int ret;
ret = ftrace_test_record(rec, enable);
ftrace_addr = (unsigned long)FTRACE_ADDR;
switch (ret) {
case FTRACE_UPDATE_IGNORE:
return 0;
case FTRACE_UPDATE_MAKE_CALL:
/* converting nop to call */
return add_brk_on_nop(rec);
case FTRACE_UPDATE_MAKE_NOP:
/* converting a call to a nop */
return add_brk_on_call(rec, ftrace_addr);
}
return 0;
}
/*
* On error, we need to remove breakpoints. This needs to
* be done caefully. If the address does not currently have a
* breakpoint, we know we are done. Otherwise, we look at the
* remaining 4 bytes of the instruction. If it matches a nop
* we replace the breakpoint with the nop. Otherwise we replace
* it with the call instruction.
*/
static int remove_breakpoint(struct dyn_ftrace *rec)
{
unsigned char ins[MCOUNT_INSN_SIZE];
unsigned char brk = BREAKPOINT_INSTRUCTION;
const unsigned char *nop;
unsigned long ftrace_addr;
unsigned long ip = rec->ip;
/* If we fail the read, just give up */
if (probe_kernel_read(ins, (void *)ip, MCOUNT_INSN_SIZE))
return -EFAULT;
/* If this does not have a breakpoint, we are done */
if (ins[0] != brk)
return -1;
nop = ftrace_nop_replace();
/*
* If the last 4 bytes of the instruction do not match
* a nop, then we assume that this is a call to ftrace_addr.
*/
if (memcmp(&ins[1], &nop[1], MCOUNT_INSN_SIZE - 1) != 0) {
/*
* For extra paranoidism, we check if the breakpoint is on
* a call that would actually jump to the ftrace_addr.
* If not, don't touch the breakpoint, we make just create
* a disaster.
*/
ftrace_addr = (unsigned long)FTRACE_ADDR;
nop = ftrace_call_replace(ip, ftrace_addr);
if (memcmp(&ins[1], &nop[1], MCOUNT_INSN_SIZE - 1) != 0)
return -EINVAL;
}
return probe_kernel_write((void *)ip, &nop[0], 1);
}
static int add_update_code(unsigned long ip, unsigned const char *new)
{
/* skip breakpoint */
ip++;
new++;
if (ftrace_write(ip, new, MCOUNT_INSN_SIZE - 1))
return -EPERM;
return 0;
}
static int add_update_call(struct dyn_ftrace *rec, unsigned long addr)
{
unsigned long ip = rec->ip;
unsigned const char *new;
new = ftrace_call_replace(ip, addr);
return add_update_code(ip, new);
}
static int add_update_nop(struct dyn_ftrace *rec)
{
unsigned long ip = rec->ip;
unsigned const char *new;
new = ftrace_nop_replace();
return add_update_code(ip, new);
}
static int add_update(struct dyn_ftrace *rec, int enable)
{
unsigned long ftrace_addr;
int ret;
ret = ftrace_test_record(rec, enable);
ftrace_addr = (unsigned long)FTRACE_ADDR;
switch (ret) {
case FTRACE_UPDATE_IGNORE:
return 0;
case FTRACE_UPDATE_MAKE_CALL:
/* converting nop to call */
return add_update_call(rec, ftrace_addr);
case FTRACE_UPDATE_MAKE_NOP:
/* converting a call to a nop */
return add_update_nop(rec);
}
return 0;
}
static int finish_update_call(struct dyn_ftrace *rec, unsigned long addr)
{
unsigned long ip = rec->ip;
unsigned const char *new;
new = ftrace_call_replace(ip, addr);
if (ftrace_write(ip, new, 1))
return -EPERM;
return 0;
}
static int finish_update_nop(struct dyn_ftrace *rec)
{
unsigned long ip = rec->ip;
unsigned const char *new;
new = ftrace_nop_replace();
if (ftrace_write(ip, new, 1))
return -EPERM;
return 0;
}
static int finish_update(struct dyn_ftrace *rec, int enable)
{
unsigned long ftrace_addr;
int ret;
ret = ftrace_update_record(rec, enable);
ftrace_addr = (unsigned long)FTRACE_ADDR;
switch (ret) {
case FTRACE_UPDATE_IGNORE:
return 0;
case FTRACE_UPDATE_MAKE_CALL:
/* converting nop to call */
return finish_update_call(rec, ftrace_addr);
case FTRACE_UPDATE_MAKE_NOP:
/* converting a call to a nop */
return finish_update_nop(rec);
}
return 0;
}
static void do_sync_core(void *data)
{
sync_core();
}
static void run_sync(void)
{
int enable_irqs = irqs_disabled();
/* We may be called with interrupts disbled (on bootup). */
if (enable_irqs)
local_irq_enable();
on_each_cpu(do_sync_core, NULL, 1);
if (enable_irqs)
local_irq_disable();
}
static void ftrace_replace_code(int enable)
{
struct ftrace_rec_iter *iter;
struct dyn_ftrace *rec;
const char *report = "adding breakpoints";
int count = 0;
int ret;
for_ftrace_rec_iter(iter) {
rec = ftrace_rec_iter_record(iter);
ret = add_breakpoints(rec, enable);
if (ret)
goto remove_breakpoints;
count++;
}
run_sync();
report = "updating code";
for_ftrace_rec_iter(iter) {
rec = ftrace_rec_iter_record(iter);
ret = add_update(rec, enable);
if (ret)
goto remove_breakpoints;
}
run_sync();
report = "removing breakpoints";
for_ftrace_rec_iter(iter) {
rec = ftrace_rec_iter_record(iter);
ret = finish_update(rec, enable);
if (ret)
goto remove_breakpoints;
}
run_sync();
return;
remove_breakpoints:
ftrace_bug(ret, rec ? rec->ip : 0);
printk(KERN_WARNING "Failed on %s (%d):\n", report, count);
for_ftrace_rec_iter(iter) {
rec = ftrace_rec_iter_record(iter);
remove_breakpoint(rec);
}
}
void arch_ftrace_update_code(int command)
{
modifying_ftrace_code++;
if (command & FTRACE_UPDATE_CALLS)
ftrace_replace_code(1);
else if (command & FTRACE_DISABLE_CALLS)
ftrace_replace_code(0);
if (command & FTRACE_UPDATE_TRACE_FUNC)
ftrace_update_ftrace_func(ftrace_trace_function);
if (command & FTRACE_START_FUNC_RET)
ftrace_enable_ftrace_graph_caller();
else if (command & FTRACE_STOP_FUNC_RET)
ftrace_disable_ftrace_graph_caller();
modifying_ftrace_code--;
}
int __init ftrace_dyn_arch_init(void *data)
{
/* The return code is retured via data */
......
......@@ -50,6 +50,7 @@
#include <asm/processor.h>
#include <asm/debugreg.h>
#include <linux/atomic.h>
#include <asm/ftrace.h>
#include <asm/traps.h>
#include <asm/desc.h>
#include <asm/i387.h>
......@@ -303,8 +304,13 @@ do_general_protection(struct pt_regs *regs, long error_code)
}
/* May run on IST stack. */
dotraplinkage void __kprobes do_int3(struct pt_regs *regs, long error_code)
dotraplinkage void __kprobes notrace do_int3(struct pt_regs *regs, long error_code)
{
#ifdef CONFIG_DYNAMIC_FTRACE
/* ftrace must be first, everything else may cause a recursive crash */
if (unlikely(modifying_ftrace_code) && ftrace_int3_handler(regs))
return;
#endif
#ifdef CONFIG_KGDB_LOW_LEVEL_TRAP
if (kgdb_ll_trap(DIE_INT3, "int3", regs, error_code, X86_TRAP_BP,
SIGTRAP) == NOTIFY_STOP)
......
......@@ -286,6 +286,12 @@ struct ftrace_rec_iter *ftrace_rec_iter_start(void);
struct ftrace_rec_iter *ftrace_rec_iter_next(struct ftrace_rec_iter *iter);
struct dyn_ftrace *ftrace_rec_iter_record(struct ftrace_rec_iter *iter);
#define for_ftrace_rec_iter(iter) \
for (iter = ftrace_rec_iter_start(); \
iter; \
iter = ftrace_rec_iter_next(iter))
int ftrace_update_record(struct dyn_ftrace *rec, int enable);
int ftrace_test_record(struct dyn_ftrace *rec, int enable);
void ftrace_run_stop_machine(int command);
......
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