MIPS: kprobe: Add support.

This patch is based on previous work by Sony and Himanshu Chauhan.

I have done some cleanup and implemented JProbes and KRETPROBES.  The
KRETPROBES part is pretty much copied verbatim from powerpc.  A possible
future enhance might be to factor out the common code.

Signed-off-by: David Daney <ddaney@caviumnetworks.com>
Cc: Himanshu Chauhan <hschauhan@nulltrace.org>
To: linux-mips@linux-mips.org
To: ananth@in.ibm.com,
To: anil.s.keshavamurthy@intel.com
To: davem@davemloft.net
To: masami.hiramatsu.pt@hitachi.com
Cc: linux-kernel@vger.kernel.org
Patchwork: https://patchwork.linux-mips.org/patch/1525/
Patchwork: https://patchwork.linux-mips.org/patch/1530/
Signed-off-by: Ralf Baechle <ralf@linux-mips.org>

3 files changed, 579 insertions, 1 deletions

diff --git a/arch/mips/kernel/Makefile b/arch/mips/kernel/Makefile
index ff5ec2e0184e..06f848299785 100644
--- a/arch/mips/kernel/Makefile
+++ b/arch/mips/kernel/Makefile
@@ -76,6 +76,7 @@ obj-$(CONFIG_IRQ_TXX9)		+= irq_txx9.o
 obj-$(CONFIG_IRQ_GT641XX)       += irq-gt641xx.o
 obj-$(CONFIG_IRQ_GIC)           += irq-gic.o
 
+obj-$(CONFIG_KPROBES)           += kprobes.o
 obj-$(CONFIG_32BIT)             += scall32-o32.o
 obj-$(CONFIG_64BIT)             += scall64-64.o
 obj-$(CONFIG_MIPS32_COMPAT)     += linux32.o ptrace32.o signal32.o
diff --git a/arch/mips/kernel/kprobes.c b/arch/mips/kernel/kprobes.c
new file mode 100644
index 000000000000..ee28683fc2ac
--- /dev/null
+++ b/arch/mips/kernel/kprobes.c
@@ -0,0 +1,557 @@
+/*
+ *  Kernel Probes (KProbes)
+ *  arch/mips/kernel/kprobes.c
+ *
+ *  Copyright 2006 Sony Corp.
+ *  Copyright 2010 Cavium Networks
+ *
+ *  Some portions copied from the powerpc version.
+ *
+ *   Copyright (C) IBM Corporation, 2002, 2004
+ *
+ *  This program is free software; you can redistribute it and/or modify
+ *  it under the terms of the GNU General Public License as published by
+ *  the Free Software Foundation; version 2 of the License.
+ *
+ *  This program is distributed in the hope that it will be useful,
+ *  but WITHOUT ANY WARRANTY; without even the implied warranty of
+ *  MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
+ *  GNU General Public License for more details.
+ *
+ *  You should have received a copy of the GNU General Public License
+ *  along with this program; if not, write to the Free Software
+ *  Foundation, Inc., 59 Temple Place, Suite 330, Boston, MA  02111-1307  USA
+ */
+
+#include <linux/kprobes.h>
+#include <linux/preempt.h>
+#include <linux/kdebug.h>
+#include <linux/slab.h>
+
+#include <asm/ptrace.h>
+#include <asm/break.h>
+#include <asm/inst.h>
+
+static const union mips_instruction breakpoint_insn = {
+        .b_format = {
+                .opcode = spec_op,
+                .code = BRK_KPROBE_BP,
+                .func = break_op
+        }
+};
+
+static const union mips_instruction breakpoint2_insn = {
+        .b_format = {
+                .opcode = spec_op,
+                .code = BRK_KPROBE_SSTEPBP,
+                .func = break_op
+        }
+};
+
+DEFINE_PER_CPU(struct kprobe *, current_kprobe);
+DEFINE_PER_CPU(struct kprobe_ctlblk, kprobe_ctlblk);
+
+static int __kprobes insn_has_delayslot(union mips_instruction insn)
+{
+        switch (insn.i_format.opcode) {
+
+                /*
+                 * This group contains:
+                 * jr and jalr are in r_format format.
+                 */
+        case spec_op:
+                switch (insn.r_format.func) {
+                case jr_op:
+                case jalr_op:
+                        break;
+                default:
+                        goto insn_ok;
+                }
+
+                /*
+                 * This group contains:
+                 * bltz_op, bgez_op, bltzl_op, bgezl_op,
+                 * bltzal_op, bgezal_op, bltzall_op, bgezall_op.
+                 */
+        case bcond_op:
+
+                /*
+                 * These are unconditional and in j_format.
+                 */
+        case jal_op:
+        case j_op:
+
+                /*
+                 * These are conditional and in i_format.
+                 */
+        case beq_op:
+        case beql_op:
+        case bne_op:
+        case bnel_op:
+        case blez_op:
+        case blezl_op:
+        case bgtz_op:
+        case bgtzl_op:
+
+                /*
+                 * These are the FPA/cp1 branch instructions.
+                 */
+        case cop1_op:
+
+#ifdef CONFIG_CPU_CAVIUM_OCTEON
+        case lwc2_op: /* This is bbit0 on Octeon */
+        case ldc2_op: /* This is bbit032 on Octeon */
+        case swc2_op: /* This is bbit1 on Octeon */
+        case sdc2_op: /* This is bbit132 on Octeon */
+#endif
+                return 1;
+        default:
+                break;
+        }
+insn_ok:
+        return 0;
+}
+
+int __kprobes arch_prepare_kprobe(struct kprobe *p)
+{
+        union mips_instruction insn;
+        union mips_instruction prev_insn;
+        int ret = 0;
+
+        prev_insn = p->addr[-1];
+        insn = p->addr[0];
+
+        if (insn_has_delayslot(insn) || insn_has_delayslot(prev_insn)) {
+                pr_notice("Kprobes for branch and jump instructions are not supported\n");
+                ret = -EINVAL;
+                goto out;
+        }
+
+        /* insn: must be on special executable page on mips. */
+        p->ainsn.insn = get_insn_slot();
+        if (!p->ainsn.insn) {
+                ret = -ENOMEM;
+                goto out;
+        }
+
+        /*
+         * In the kprobe->ainsn.insn[] array we store the original
+         * instruction at index zero and a break trap instruction at
+         * index one.
+         */
+
+        memcpy(&p->ainsn.insn[0], p->addr, sizeof(kprobe_opcode_t));
+        p->ainsn.insn[1] = breakpoint2_insn;
+        p->opcode = *p->addr;
+
+out:
+        return ret;
+}
+
+void __kprobes arch_arm_kprobe(struct kprobe *p)
+{
+        *p->addr = breakpoint_insn;
+        flush_insn_slot(p);
+}
+
+void __kprobes arch_disarm_kprobe(struct kprobe *p)
+{
+        *p->addr = p->opcode;
+        flush_insn_slot(p);
+}
+
+void __kprobes arch_remove_kprobe(struct kprobe *p)
+{
+        free_insn_slot(p->ainsn.insn, 0);
+}
+
+static void save_previous_kprobe(struct kprobe_ctlblk *kcb)
+{
+        kcb->prev_kprobe.kp = kprobe_running();
+        kcb->prev_kprobe.status = kcb->kprobe_status;
+        kcb->prev_kprobe.old_SR = kcb->kprobe_old_SR;
+        kcb->prev_kprobe.saved_SR = kcb->kprobe_saved_SR;
+        kcb->prev_kprobe.saved_epc = kcb->kprobe_saved_epc;
+}
+
+static void restore_previous_kprobe(struct kprobe_ctlblk *kcb)
+{
+        __get_cpu_var(current_kprobe) = kcb->prev_kprobe.kp;
+        kcb->kprobe_status = kcb->prev_kprobe.status;
+        kcb->kprobe_old_SR = kcb->prev_kprobe.old_SR;
+        kcb->kprobe_saved_SR = kcb->prev_kprobe.saved_SR;
+        kcb->kprobe_saved_epc = kcb->prev_kprobe.saved_epc;
+}
+
+static void set_current_kprobe(struct kprobe *p, struct pt_regs *regs,
+                               struct kprobe_ctlblk *kcb)
+{
+        __get_cpu_var(current_kprobe) = p;
+        kcb->kprobe_saved_SR = kcb->kprobe_old_SR = (regs->cp0_status & ST0_IE);
+        kcb->kprobe_saved_epc = regs->cp0_epc;
+}
+
+static void prepare_singlestep(struct kprobe *p, struct pt_regs *regs)
+{
+        regs->cp0_status &= ~ST0_IE;
+
+        /* single step inline if the instruction is a break */
+        if (p->opcode.word == breakpoint_insn.word ||
+            p->opcode.word == breakpoint2_insn.word)
+                regs->cp0_epc = (unsigned long)p->addr;
+        else
+                regs->cp0_epc = (unsigned long)&p->ainsn.insn[0];
+}
+
+static int __kprobes kprobe_handler(struct pt_regs *regs)
+{
+        struct kprobe *p;
+        int ret = 0;
+        kprobe_opcode_t *addr;
+        struct kprobe_ctlblk *kcb;
+
+        addr = (kprobe_opcode_t *) regs->cp0_epc;
+
+        /*
+         * We don't want to be preempted for the entire
+         * duration of kprobe processing
+         */
+        preempt_disable();
+        kcb = get_kprobe_ctlblk();
+
+        /* Check we're not actually recursing */
+        if (kprobe_running()) {
+                p = get_kprobe(addr);
+                if (p) {
+                        if (kcb->kprobe_status == KPROBE_HIT_SS &&
+                            p->ainsn.insn->word == breakpoint_insn.word) {
+                                regs->cp0_status &= ~ST0_IE;
+                                regs->cp0_status |= kcb->kprobe_saved_SR;
+                                goto no_kprobe;
+                        }
+                        /*
+                         * We have reentered the kprobe_handler(), since
+                         * another probe was hit while within the handler.
+                         * We here save the original kprobes variables and
+                         * just single step on the instruction of the new probe
+                         * without calling any user handlers.
+                         */
+                        save_previous_kprobe(kcb);
+                        set_current_kprobe(p, regs, kcb);
+                        kprobes_inc_nmissed_count(p);
+                        prepare_singlestep(p, regs);
+                        kcb->kprobe_status = KPROBE_REENTER;
+                        return 1;
+                } else {
+                        if (addr->word != breakpoint_insn.word) {
+                                /*
+                                 * The breakpoint instruction was removed by
+                                 * another cpu right after we hit, no further
+                                 * handling of this interrupt is appropriate
+                                 */
+                                ret = 1;
+                                goto no_kprobe;
+                        }
+                        p = __get_cpu_var(current_kprobe);
+                        if (p->break_handler && p->break_handler(p, regs))
+                                goto ss_probe;
+                }
+                goto no_kprobe;
+        }
+
+        p = get_kprobe(addr);
+        if (!p) {
+                if (addr->word != breakpoint_insn.word) {
+                        /*
+                         * The breakpoint instruction was removed right
+                         * after we hit it.  Another cpu has removed
+                         * either a probepoint or a debugger breakpoint
+                         * at this address.  In either case, no further
+                         * handling of this interrupt is appropriate.
+                         */
+                        ret = 1;
+                }
+                /* Not one of ours: let kernel handle it */
+                goto no_kprobe;
+        }
+
+        set_current_kprobe(p, regs, kcb);
+        kcb->kprobe_status = KPROBE_HIT_ACTIVE;
+
+        if (p->pre_handler && p->pre_handler(p, regs)) {
+                /* handler has already set things up, so skip ss setup */
+                return 1;
+        }
+
+ss_probe:
+        prepare_singlestep(p, regs);
+        kcb->kprobe_status = KPROBE_HIT_SS;
+        return 1;
+
+no_kprobe:
+        preempt_enable_no_resched();
+        return ret;
+
+}
+
+/*
+ * Called after single-stepping.  p->addr is the address of the
+ * instruction whose first byte has been replaced by the "break 0"
+ * instruction.  To avoid the SMP problems that can occur when we
+ * temporarily put back the original opcode to single-step, we
+ * single-stepped a copy of the instruction.  The address of this
+ * copy is p->ainsn.insn.
+ *
+ * This function prepares to return from the post-single-step
+ * breakpoint trap.
+ */
+static void __kprobes resume_execution(struct kprobe *p,
+                                       struct pt_regs *regs,
+                                       struct kprobe_ctlblk *kcb)
+{
+        unsigned long orig_epc = kcb->kprobe_saved_epc;
+        regs->cp0_epc = orig_epc + 4;
+}
+
+static inline int post_kprobe_handler(struct pt_regs *regs)
+{
+        struct kprobe *cur = kprobe_running();
+        struct kprobe_ctlblk *kcb = get_kprobe_ctlblk();
+
+        if (!cur)
+                return 0;
+
+        if ((kcb->kprobe_status != KPROBE_REENTER) && cur->post_handler) {
+                kcb->kprobe_status = KPROBE_HIT_SSDONE;
+                cur->post_handler(cur, regs, 0);
+        }
+
+        resume_execution(cur, regs, kcb);
+
+        regs->cp0_status |= kcb->kprobe_saved_SR;
+
+        /* Restore back the original saved kprobes variables and continue. */
+        if (kcb->kprobe_status == KPROBE_REENTER) {
+                restore_previous_kprobe(kcb);
+                goto out;
+        }
+        reset_current_kprobe();
+out:
+        preempt_enable_no_resched();
+
+        return 1;
+}
+
+static inline int kprobe_fault_handler(struct pt_regs *regs, int trapnr)
+{
+        struct kprobe *cur = kprobe_running();
+        struct kprobe_ctlblk *kcb = get_kprobe_ctlblk();
+
+        if (cur->fault_handler && cur->fault_handler(cur, regs, trapnr))
+                return 1;
+
+        if (kcb->kprobe_status & KPROBE_HIT_SS) {
+                resume_execution(cur, regs, kcb);
+                regs->cp0_status |= kcb->kprobe_old_SR;
+
+                reset_current_kprobe();
+                preempt_enable_no_resched();
+        }
+        return 0;
+}
+
+/*
+ * Wrapper routine for handling exceptions.
+ */
+int __kprobes kprobe_exceptions_notify(struct notifier_block *self,
+                                       unsigned long val, void *data)
+{
+
+        struct die_args *args = (struct die_args *)data;
+        int ret = NOTIFY_DONE;
+
+        switch (val) {
+        case DIE_BREAK:
+                if (kprobe_handler(args->regs))
+                        ret = NOTIFY_STOP;
+                break;
+        case DIE_SSTEPBP:
+                if (post_kprobe_handler(args->regs))
+                        ret = NOTIFY_STOP;
+                break;
+
+        case DIE_PAGE_FAULT:
+                /* kprobe_running() needs smp_processor_id() */
+                preempt_disable();
+
+                if (kprobe_running()
+                    && kprobe_fault_handler(args->regs, args->trapnr))
+                        ret = NOTIFY_STOP;
+                preempt_enable();
+                break;
+        default:
+                break;
+        }
+        return ret;
+}
+
+int __kprobes setjmp_pre_handler(struct kprobe *p, struct pt_regs *regs)
+{
+        struct jprobe *jp = container_of(p, struct jprobe, kp);
+        struct kprobe_ctlblk *kcb = get_kprobe_ctlblk();
+
+        kcb->jprobe_saved_regs = *regs;
+        kcb->jprobe_saved_sp = regs->regs[29];
+
+        memcpy(kcb->jprobes_stack, (void *)kcb->jprobe_saved_sp,
+               MIN_JPROBES_STACK_SIZE(kcb->jprobe_saved_sp));
+
+        regs->cp0_epc = (unsigned long)(jp->entry);
+
+        return 1;
+}
+
+/* Defined in the inline asm below. */
+void jprobe_return_end(void);
+
+void __kprobes jprobe_return(void)
+{
+        /* Assembler quirk necessitates this '0,code' business.  */
+        asm volatile(
+                "break 0,%0\n\t"
+                ".globl jprobe_return_end\n"
+                "jprobe_return_end:\n"
+                : : "n" (BRK_KPROBE_BP) : "memory");
+}
+
+int __kprobes longjmp_break_handler(struct kprobe *p, struct pt_regs *regs)
+{
+        struct kprobe_ctlblk *kcb = get_kprobe_ctlblk();
+
+        if (regs->cp0_epc >= (unsigned long)jprobe_return &&
+            regs->cp0_epc <= (unsigned long)jprobe_return_end) {
+                *regs = kcb->jprobe_saved_regs;
+                memcpy((void *)kcb->jprobe_saved_sp, kcb->jprobes_stack,
+                       MIN_JPROBES_STACK_SIZE(kcb->jprobe_saved_sp));
+                preempt_enable_no_resched();
+
+                return 1;
+        }
+        return 0;
+}
+
+/*
+ * Function return probe trampoline:
+ *      - init_kprobes() establishes a probepoint here
+ *      - When the probed function returns, this probe causes the
+ *        handlers to fire
+ */
+static void __used kretprobe_trampoline_holder(void)
+{
+        asm volatile(
+                ".set push\n\t"
+                /* Keep the assembler from reordering and placing JR here. */
+                ".set noreorder\n\t"
+                "nop\n\t"
+                ".global kretprobe_trampoline\n"
+                "kretprobe_trampoline:\n\t"
+                "nop\n\t"
+                ".set pop"
+                : : : "memory");
+}
+
+void kretprobe_trampoline(void);
+
+void __kprobes arch_prepare_kretprobe(struct kretprobe_instance *ri,
+                                      struct pt_regs *regs)
+{
+        ri->ret_addr = (kprobe_opcode_t *) regs->regs[31];
+
+        /* Replace the return addr with trampoline addr */
+        regs->regs[31] = (unsigned long)kretprobe_trampoline;
+}
+
+/*
+ * Called when the probe at kretprobe trampoline is hit
+ */
+static int __kprobes trampoline_probe_handler(struct kprobe *p,
+                                                struct pt_regs *regs)
+{
+        struct kretprobe_instance *ri = NULL;
+        struct hlist_head *head, empty_rp;
+        struct hlist_node *node, *tmp;
+        unsigned long flags, orig_ret_address = 0;
+        unsigned long trampoline_address = (unsigned long)kretprobe_trampoline;
+
+        INIT_HLIST_HEAD(&empty_rp);
+        kretprobe_hash_lock(current, &head, &flags);
+
+        /*
+         * It is possible to have multiple instances associated with a given
+         * task either because an multiple functions in the call path
+         * have a return probe installed on them, and/or more than one return
+         * return probe was registered for a target function.
+         *
+         * We can handle this because:
+         *     - instances are always inserted at the head of the list
+         *     - when multiple return probes are registered for the same
+         *       function, the first instance's ret_addr will point to the
+         *       real return address, and all the rest will point to
+         *       kretprobe_trampoline
+         */
+        hlist_for_each_entry_safe(ri, node, tmp, head, hlist) {
+                if (ri->task != current)
+                        /* another task is sharing our hash bucket */
+                        continue;
+
+                if (ri->rp && ri->rp->handler)
+                        ri->rp->handler(ri, regs);
+
+                orig_ret_address = (unsigned long)ri->ret_addr;
+                recycle_rp_inst(ri, &empty_rp);
+
+                if (orig_ret_address != trampoline_address)
+                        /*
+                         * This is the real return address. Any other
+                         * instances associated with this task are for
+                         * other calls deeper on the call stack
+                         */
+                        break;
+        }
+
+        kretprobe_assert(ri, orig_ret_address, trampoline_address);
+        instruction_pointer(regs) = orig_ret_address;
+
+        reset_current_kprobe();
+        kretprobe_hash_unlock(current, &flags);
+        preempt_enable_no_resched();
+
+        hlist_for_each_entry_safe(ri, node, tmp, &empty_rp, hlist) {
+                hlist_del(&ri->hlist);
+                kfree(ri);
+        }
+        /*
+         * By returning a non-zero value, we are telling
+         * kprobe_handler() that we don't want the post_handler
+         * to run (and have re-enabled preemption)
+         */
+        return 1;
+}
+
+int __kprobes arch_trampoline_kprobe(struct kprobe *p)
+{
+        if (p->addr == (kprobe_opcode_t *)kretprobe_trampoline)
+                return 1;
+
+        return 0;
+}
+
+static struct kprobe trampoline_p = {
+        .addr = (kprobe_opcode_t *)kretprobe_trampoline,
+        .pre_handler = trampoline_probe_handler
+};
+
+int __init arch_init_kprobes(void)
+{
+        return register_kprobe(&trampoline_p);
+}
diff --git a/arch/mips/kernel/traps.c b/arch/mips/kernel/traps.c
index 1515b673179d..4c6079f24958 100644
--- a/arch/mips/kernel/traps.c
+++ b/arch/mips/kernel/traps.c
@@ -25,6 +25,7 @@
 #include <linux/ptrace.h>
 #include <linux/kgdb.h>
 #include <linux/kdebug.h>
+#include <linux/kprobes.h>
 #include <linux/notifier.h>
 #include <linux/kdb.h>
 
@@ -334,7 +335,7 @@ void show_regs(struct pt_regs *regs)
         __show_regs((struct pt_regs *)regs);
 }
 
-void show_registers(const struct pt_regs *regs)
+void show_registers(struct pt_regs *regs)
 {
         const int field = 2 * sizeof(unsigned long);
 
@@ -783,6 +784,25 @@ asmlinkage void do_bp(struct pt_regs *regs)
         if (bcode >= (1 << 10))
                 bcode >>= 10;
 
+        /*
+         * notify the kprobe handlers, if instruction is likely to
+         * pertain to them.
+         */
+        switch (bcode) {
+        case BRK_KPROBE_BP:
+                if (notify_die(DIE_BREAK, "debug", regs, bcode, 0, 0) == NOTIFY_STOP)
+                        return;
+                else
+                        break;
+        case BRK_KPROBE_SSTEPBP:
+                if (notify_die(DIE_SSTEPBP, "single_step", regs, bcode, 0, 0) == NOTIFY_STOP)
+                        return;
+                else
+                        break;
+        default:
+                break;
+        }
+
         do_trap_or_bp(regs, bcode, "Break");
         return;