1 files changed, 332 insertions, 168 deletions

diff --git a/arch/x86/kernel/ftrace.c b/arch/x86/kernel/ftrace.c
index c9a281f272fd..32ff36596ab1 100644
--- a/arch/x86/kernel/ftrace.c
+++ b/arch/x86/kernel/ftrace.c
@@ -24,40 +24,21 @@
 #include <trace/syscall.h>
 
 #include <asm/cacheflush.h>
+#include <asm/kprobes.h>
 #include <asm/ftrace.h>
 #include <asm/nops.h>
-#include <asm/nmi.h>
-
 
 #ifdef CONFIG_DYNAMIC_FTRACE
 
-/*
- * modifying_code is set to notify NMIs that they need to use
- * memory barriers when entering or exiting. But we don't want
- * to burden NMIs with unnecessary memory barriers when code
- * modification is not being done (which is most of the time).
- *
- * A mutex is already held when ftrace_arch_code_modify_prepare
- * and post_process are called. No locks need to be taken here.
- *
- * Stop machine will make sure currently running NMIs are done
- * and new NMIs will see the updated variable before we need
- * to worry about NMIs doing memory barriers.
- */
-static int modifying_code __read_mostly;
-static DEFINE_PER_CPU(int, save_modifying_code);
-
 int ftrace_arch_code_modify_prepare(void)
 {
         set_kernel_text_rw();
         set_all_modules_text_rw();
-        modifying_code = 1;
         return 0;
 }
 
 int ftrace_arch_code_modify_post_process(void)
 {
-        modifying_code = 0;
         set_all_modules_text_ro();
         set_kernel_text_ro();
         return 0;
@@ -90,134 +71,6 @@ static unsigned char *ftrace_call_replace(unsigned long ip, unsigned long addr)
         return calc.code;
 }
 
-/*
- * Modifying code must take extra care. On an SMP machine, if
- * the code being modified is also being executed on another CPU
- * that CPU will have undefined results and possibly take a GPF.
- * We use kstop_machine to stop other CPUS from exectuing code.
- * But this does not stop NMIs from happening. We still need
- * to protect against that. We separate out the modification of
- * the code to take care of this.
- *
- * Two buffers are added: An IP buffer and a "code" buffer.
- *
- * 1) Put the instruction pointer into the IP buffer
- *    and the new code into the "code" buffer.
- * 2) Wait for any running NMIs to finish and set a flag that says
- *    we are modifying code, it is done in an atomic operation.
- * 3) Write the code
- * 4) clear the flag.
- * 5) Wait for any running NMIs to finish.
- *
- * If an NMI is executed, the first thing it does is to call
- * "ftrace_nmi_enter". This will check if the flag is set to write
- * and if it is, it will write what is in the IP and "code" buffers.
- *
- * The trick is, it does not matter if everyone is writing the same
- * content to the code location. Also, if a CPU is executing code
- * it is OK to write to that code location if the contents being written
- * are the same as what exists.
- */
-
-#define MOD_CODE_WRITE_FLAG (1 << 31)   /* set when NMI should do the write */
-static atomic_t nmi_running = ATOMIC_INIT(0);
-static int mod_code_status;             /* holds return value of text write */
-static void *mod_code_ip;               /* holds the IP to write to */
-static const void *mod_code_newcode;    /* holds the text to write to the IP */
-
-static unsigned nmi_wait_count;
-static atomic_t nmi_update_count = ATOMIC_INIT(0);
-
-int ftrace_arch_read_dyn_info(char *buf, int size)
-{
-        int r;
-
-        r = snprintf(buf, size, "%u %u",
-                     nmi_wait_count,
-                     atomic_read(&nmi_update_count));
-        return r;
-}
-
-static void clear_mod_flag(void)
-{
-        int old = atomic_read(&nmi_running);
-
-        for (;;) {
-                int new = old & ~MOD_CODE_WRITE_FLAG;
-
-                if (old == new)
-                        break;
-
-                old = atomic_cmpxchg(&nmi_running, old, new);
-        }
-}
-
-static void ftrace_mod_code(void)
-{
-        /*
-         * Yes, more than one CPU process can be writing to mod_code_status.
-         *    (and the code itself)
-         * But if one were to fail, then they all should, and if one were
-         * to succeed, then they all should.
-         */
-        mod_code_status = probe_kernel_write(mod_code_ip, mod_code_newcode,
-                                             MCOUNT_INSN_SIZE);
-
-        /* if we fail, then kill any new writers */
-        if (mod_code_status)
-                clear_mod_flag();
-}
-
-void ftrace_nmi_enter(void)
-{
-        __this_cpu_write(save_modifying_code, modifying_code);
-
-        if (!__this_cpu_read(save_modifying_code))
-                return;
-
-        if (atomic_inc_return(&nmi_running) & MOD_CODE_WRITE_FLAG) {
-                smp_rmb();
-                ftrace_mod_code();
-                atomic_inc(&nmi_update_count);
-        }
-        /* Must have previous changes seen before executions */
-        smp_mb();
-}
-
-void ftrace_nmi_exit(void)
-{
-        if (!__this_cpu_read(save_modifying_code))
-                return;
-
-        /* Finish all executions before clearing nmi_running */
-        smp_mb();
-        atomic_dec(&nmi_running);
-}
-
-static void wait_for_nmi_and_set_mod_flag(void)
-{
-        if (!atomic_cmpxchg(&nmi_running, 0, MOD_CODE_WRITE_FLAG))
-                return;
-
-        do {
-                cpu_relax();
-        } while (atomic_cmpxchg(&nmi_running, 0, MOD_CODE_WRITE_FLAG));
-
-        nmi_wait_count++;
-}
-
-static void wait_for_nmi(void)
-{
-        if (!atomic_read(&nmi_running))
-                return;
-
-        do {
-                cpu_relax();
-        } while (atomic_read(&nmi_running));
-
-        nmi_wait_count++;
-}
-
 static inline int
 within(unsigned long addr, unsigned long start, unsigned long end)
 {
@@ -238,26 +91,7 @@ do_ftrace_mod_code(unsigned long ip, const void *new_code)
         if (within(ip, (unsigned long)_text, (unsigned long)_etext))
                 ip = (unsigned long)__va(__pa(ip));
 
-        mod_code_ip = (void *)ip;
-        mod_code_newcode = new_code;
-
-        /* The buffers need to be visible before we let NMIs write them */
-        smp_mb();
-
-        wait_for_nmi_and_set_mod_flag();
-
-        /* Make sure all running NMIs have finished before we write the code */
-        smp_mb();
-
-        ftrace_mod_code();
-
-        /* Make sure the write happens before clearing the bit */
-        smp_mb();
-
-        clear_mod_flag();
-        wait_for_nmi();
-
-        return mod_code_status;
+        return probe_kernel_write((void *)ip, new_code, MCOUNT_INSN_SIZE);
 }
 
 static const unsigned char *ftrace_nop_replace(void)
@@ -334,6 +168,336 @@ 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();
+}
+
+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++;
+
+        ftrace_modify_all_code(command);
+
+        modifying_ftrace_code--;
+}
+
 int __init ftrace_dyn_arch_init(void *data)
 {
         /* The return code is retured via data */