4 files changed, 358 insertions, 1 deletions

diff --git a/arch/x86/include/asm/ftrace.h b/arch/x86/include/asm/ftrace.h
index 268c783ab1c0..18d9005d9e4f 100644
--- a/arch/x86/include/asm/ftrace.h
+++ b/arch/x86/include/asm/ftrace.h
@@ -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 */
diff --git a/arch/x86/kernel/ftrace.c b/arch/x86/kernel/ftrace.c
index c9a281f272fd..80af34739a9a 100644
--- a/arch/x86/kernel/ftrace.c
+++ b/arch/x86/kernel/ftrace.c
@@ -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 */
diff --git a/arch/x86/kernel/traps.c b/arch/x86/kernel/traps.c
index ff9281f16029..92d5756d85fc 100644
--- a/arch/x86/kernel/traps.c
+++ b/arch/x86/kernel/traps.c
@@ -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 @@ gp_in_kernel:
 }
 
 /* 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)
diff --git a/include/linux/ftrace.h b/include/linux/ftrace.h
index 72a6cabb4d5b..0b5590330bca 100644
--- a/include/linux/ftrace.h
+++ b/include/linux/ftrace.h
@@ -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);