ARM: 6357/1: hw-breakpoint: add new ptrace requests for hw-breakpoint interaction

For debuggers to take advantage of the hw-breakpoint framework in the kernel,
it is necessary to expose the API calls via a ptrace interface.

This patch exposes the hardware breakpoints framework as a collection of
virtual registers, accesible using PTRACE_SETHBPREGS and PTRACE_GETHBPREGS
requests. The breakpoints are stored in the debug_info struct of the running
thread.

Cc: Frederic Weisbecker <fweisbec@gmail.com>
Cc: S. Karthikeyan <informkarthik@gmail.com>
Signed-off-by: Will Deacon <will.deacon@arm.com>
Signed-off-by: Russell King <rmk+kernel@arm.linux.org.uk>

2 files changed, 244 insertions, 0 deletions

diff --git a/arch/arm/kernel/process.c b/arch/arm/kernel/process.c
index 401e38be1f78..974af1c3eb1d 100644
--- a/arch/arm/kernel/process.c
+++ b/arch/arm/kernel/process.c
@@ -29,6 +29,7 @@
 #include <linux/utsname.h>
 #include <linux/uaccess.h>
 #include <linux/random.h>
+#include <linux/hw_breakpoint.h>
 
 #include <asm/cacheflush.h>
 #include <asm/leds.h>
@@ -317,6 +318,8 @@ void flush_thread(void)
         struct thread_info *thread = current_thread_info();
         struct task_struct *tsk = current;
 
+        flush_ptrace_hw_breakpoint(tsk);
+
         memset(thread->used_cp, 0, sizeof(thread->used_cp));
         memset(&tsk->thread.debug, 0, sizeof(struct debug_info));
         memset(&thread->fpstate, 0, sizeof(union fp_state));
@@ -345,6 +348,8 @@ copy_thread(unsigned long clone_flags, unsigned long stack_start,
         thread->cpu_context.sp = (unsigned long)childregs;
         thread->cpu_context.pc = (unsigned long)ret_from_fork;
 
+        clear_ptrace_hw_breakpoint(p);
+
         if (clone_flags & CLONE_SETTLS)
                 thread->tp_value = regs->ARM_r3;
 
diff --git a/arch/arm/kernel/ptrace.c b/arch/arm/kernel/ptrace.c
index f99d489822d5..e0cb6370ed14 100644
--- a/arch/arm/kernel/ptrace.c
+++ b/arch/arm/kernel/ptrace.c
@@ -19,6 +19,8 @@
 #include <linux/init.h>
 #include <linux/signal.h>
 #include <linux/uaccess.h>
+#include <linux/perf_event.h>
+#include <linux/hw_breakpoint.h>
 
 #include <asm/pgtable.h>
 #include <asm/system.h>
@@ -847,6 +849,232 @@ static int ptrace_setvfpregs(struct task_struct *tsk, void __user *data)
 }
 #endif
 
+#ifdef CONFIG_HAVE_HW_BREAKPOINT
+/*
+ * Convert a virtual register number into an index for a thread_info
+ * breakpoint array. Breakpoints are identified using positive numbers
+ * whilst watchpoints are negative. The registers are laid out as pairs
+ * of (address, control), each pair mapping to a unique hw_breakpoint struct.
+ * Register 0 is reserved for describing resource information.
+ */
+static int ptrace_hbp_num_to_idx(long num)
+{
+        if (num < 0)
+                num = (ARM_MAX_BRP << 1) - num;
+        return (num - 1) >> 1;
+}
+
+/*
+ * Returns the virtual register number for the address of the
+ * breakpoint at index idx.
+ */
+static long ptrace_hbp_idx_to_num(int idx)
+{
+        long mid = ARM_MAX_BRP << 1;
+        long num = (idx << 1) + 1;
+        return num > mid ? mid - num : num;
+}
+
+/*
+ * Handle hitting a HW-breakpoint.
+ */
+static void ptrace_hbptriggered(struct perf_event *bp, int unused,
+                                     struct perf_sample_data *data,
+                                     struct pt_regs *regs)
+{
+        struct arch_hw_breakpoint *bkpt = counter_arch_bp(bp);
+        long num;
+        int i;
+        siginfo_t info;
+
+        for (i = 0; i < ARM_MAX_HBP_SLOTS; ++i)
+                if (current->thread.debug.hbp[i] == bp)
+                        break;
+
+        num = (i == ARM_MAX_HBP_SLOTS) ? 0 : ptrace_hbp_idx_to_num(i);
+
+        info.si_signo   = SIGTRAP;
+        info.si_errno   = (int)num;
+        info.si_code    = TRAP_HWBKPT;
+        info.si_addr    = (void __user *)(bkpt->trigger);
+
+        force_sig_info(SIGTRAP, &info, current);
+}
+
+/*
+ * Set ptrace breakpoint pointers to zero for this task.
+ * This is required in order to prevent child processes from unregistering
+ * breakpoints held by their parent.
+ */
+void clear_ptrace_hw_breakpoint(struct task_struct *tsk)
+{
+        memset(tsk->thread.debug.hbp, 0, sizeof(tsk->thread.debug.hbp));
+}
+
+/*
+ * Unregister breakpoints from this task and reset the pointers in
+ * the thread_struct.
+ */
+void flush_ptrace_hw_breakpoint(struct task_struct *tsk)
+{
+        int i;
+        struct thread_struct *t = &tsk->thread;
+
+        for (i = 0; i < ARM_MAX_HBP_SLOTS; i++) {
+                if (t->debug.hbp[i]) {
+                        unregister_hw_breakpoint(t->debug.hbp[i]);
+                        t->debug.hbp[i] = NULL;
+                }
+        }
+}
+
+static u32 ptrace_get_hbp_resource_info(void)
+{
+        u8 num_brps, num_wrps, debug_arch, wp_len;
+        u32 reg = 0;
+
+        num_brps        = hw_breakpoint_slots(TYPE_INST);
+        num_wrps        = hw_breakpoint_slots(TYPE_DATA);
+        debug_arch      = arch_get_debug_arch();
+        wp_len          = arch_get_max_wp_len();
+
+        reg             |= debug_arch;
+        reg             <<= 8;
+        reg             |= wp_len;
+        reg             <<= 8;
+        reg             |= num_wrps;
+        reg             <<= 8;
+        reg             |= num_brps;
+
+        return reg;
+}
+
+static struct perf_event *ptrace_hbp_create(struct task_struct *tsk, int type)
+{
+        struct perf_event_attr attr;
+
+        ptrace_breakpoint_init(&attr);
+
+        /* Initialise fields to sane defaults. */
+        attr.bp_addr    = 0;
+        attr.bp_len     = HW_BREAKPOINT_LEN_4;
+        attr.bp_type    = type;
+        attr.disabled   = 1;
+
+        return register_user_hw_breakpoint(&attr, ptrace_hbptriggered, tsk);
+}
+
+static int ptrace_gethbpregs(struct task_struct *tsk, long num,
+                             unsigned long  __user *data)
+{
+        u32 reg;
+        int idx, ret = 0;
+        struct perf_event *bp;
+        struct arch_hw_breakpoint_ctrl arch_ctrl;
+
+        if (num == 0) {
+                reg = ptrace_get_hbp_resource_info();
+        } else {
+                idx = ptrace_hbp_num_to_idx(num);
+                if (idx < 0 || idx >= ARM_MAX_HBP_SLOTS) {
+                        ret = -EINVAL;
+                        goto out;
+                }
+
+                bp = tsk->thread.debug.hbp[idx];
+                if (!bp) {
+                        reg = 0;
+                        goto put;
+                }
+
+                arch_ctrl = counter_arch_bp(bp)->ctrl;
+
+                /*
+                 * Fix up the len because we may have adjusted it
+                 * to compensate for an unaligned address.
+                 */
+                while (!(arch_ctrl.len & 0x1))
+                        arch_ctrl.len >>= 1;
+
+                if (idx & 0x1)
+                        reg = encode_ctrl_reg(arch_ctrl);
+                else
+                        reg = bp->attr.bp_addr;
+        }
+
+put:
+        if (put_user(reg, data))
+                ret = -EFAULT;
+
+out:
+        return ret;
+}
+
+static int ptrace_sethbpregs(struct task_struct *tsk, long num,
+                             unsigned long __user *data)
+{
+        int idx, gen_len, gen_type, implied_type, ret = 0;
+        u32 user_val;
+        struct perf_event *bp;
+        struct arch_hw_breakpoint_ctrl ctrl;
+        struct perf_event_attr attr;
+
+        if (num == 0)
+                goto out;
+        else if (num < 0)
+                implied_type = HW_BREAKPOINT_RW;
+        else
+                implied_type = HW_BREAKPOINT_X;
+
+        idx = ptrace_hbp_num_to_idx(num);
+        if (idx < 0 || idx >= ARM_MAX_HBP_SLOTS) {
+                ret = -EINVAL;
+                goto out;
+        }
+
+        if (get_user(user_val, data)) {
+                ret = -EFAULT;
+                goto out;
+        }
+
+        bp = tsk->thread.debug.hbp[idx];
+        if (!bp) {
+                bp = ptrace_hbp_create(tsk, implied_type);
+                if (IS_ERR(bp)) {
+                        ret = PTR_ERR(bp);
+                        goto out;
+                }
+                tsk->thread.debug.hbp[idx] = bp;
+        }
+
+        attr = bp->attr;
+
+        if (num & 0x1) {
+                /* Address */
+                attr.bp_addr    = user_val;
+        } else {
+                /* Control */
+                decode_ctrl_reg(user_val, &ctrl);
+                ret = arch_bp_generic_fields(ctrl, &gen_len, &gen_type);
+                if (ret)
+                        goto out;
+
+                if ((gen_type & implied_type) != gen_type) {
+                                ret = -EINVAL;
+                                goto out;
+                }
+
+                attr.bp_len     = gen_len;
+                attr.bp_type    = gen_type;
+                attr.disabled   = !ctrl.enabled;
+        }
+
+        ret = modify_user_hw_breakpoint(bp, &attr);
+out:
+        return ret;
+}
+#endif
+
 long arch_ptrace(struct task_struct *child, long request, long addr, long data)
 {
         int ret;
@@ -916,6 +1144,17 @@ long arch_ptrace(struct task_struct *child, long request, long addr, long data)
                         break;
 #endif
 
+#ifdef CONFIG_HAVE_HW_BREAKPOINT
+                case PTRACE_GETHBPREGS:
+                        ret = ptrace_gethbpregs(child, addr,
+                                                (unsigned long __user *)data);
+                        break;
+                case PTRACE_SETHBPREGS:
+                        ret = ptrace_sethbpregs(child, addr,
+                                                (unsigned long __user *)data);
+                        break;
+#endif
+
                 default:
                         ret = ptrace_request(child, request, addr, data);
                         break;