1 files changed, 123 insertions, 36 deletions

diff --git a/arch/arm/kernel/hw_breakpoint.c b/arch/arm/kernel/hw_breakpoint.c
index 02ca7adf5375..054e9199f30d 100644
--- a/arch/arm/kernel/hw_breakpoint.c
+++ b/arch/arm/kernel/hw_breakpoint.c
@@ -547,7 +547,7 @@ static int arch_build_bp_info(struct perf_event *bp,
 		if ((hw->ctrl.type != ARM_BREAKPOINT_EXECUTE)
 			&& max_watchpoint_len >= 8)
 			break;
-		/* Else, fall through */
+		fallthrough;
 	default:
 		return -EINVAL;
 	}
@@ -612,12 +612,12 @@ int hw_breakpoint_arch_parse(struct perf_event *bp,
 		/* Allow halfword watchpoints and breakpoints. */
 		if (hw->ctrl.len == ARM_BREAKPOINT_LEN_2)
 			break;
-		/* Else, fall through */
+		fallthrough;
 	case 3:
 		/* Allow single byte watchpoint. */
 		if (hw->ctrl.len == ARM_BREAKPOINT_LEN_1)
 			break;
-		/* Else, fall through */
+		fallthrough;
 	default:
 		ret = -EINVAL;
 		goto out;
@@ -683,26 +683,68 @@ static void disable_single_step(struct perf_event *bp)
 	arch_install_hw_breakpoint(bp);
 }
 
+/*
+ * Arm32 hardware does not always report a watchpoint hit address that matches
+ * one of the watchpoints set. It can also report an address "near" the
+ * watchpoint if a single instruction access both watched and unwatched
+ * addresses. There is no straight-forward way, short of disassembling the
+ * offending instruction, to map that address back to the watchpoint. This
+ * function computes the distance of the memory access from the watchpoint as a
+ * heuristic for the likelyhood that a given access triggered the watchpoint.
+ *
+ * See this same function in the arm64 platform code, which has the same
+ * problem.
+ *
+ * The function returns the distance of the address from the bytes watched by
+ * the watchpoint. In case of an exact match, it returns 0.
+ */
+static u32 get_distance_from_watchpoint(unsigned long addr, u32 val,
+					struct arch_hw_breakpoint_ctrl *ctrl)
+{
+	u32 wp_low, wp_high;
+	u32 lens, lene;
+
+	lens = __ffs(ctrl->len);
+	lene = __fls(ctrl->len);
+
+	wp_low = val + lens;
+	wp_high = val + lene;
+	if (addr < wp_low)
+		return wp_low - addr;
+	else if (addr > wp_high)
+		return addr - wp_high;
+	else
+		return 0;
+}
+
+static int watchpoint_fault_on_uaccess(struct pt_regs *regs,
+				       struct arch_hw_breakpoint *info)
+{
+	return !user_mode(regs) && info->ctrl.privilege == ARM_BREAKPOINT_USER;
+}
+
 static void watchpoint_handler(unsigned long addr, unsigned int fsr,
 			       struct pt_regs *regs)
 {
-	int i, access;
-	u32 val, ctrl_reg, alignment_mask;
+	int i, access, closest_match = 0;
+	u32 min_dist = -1, dist;
+	u32 val, ctrl_reg;
 	struct perf_event *wp, **slots;
 	struct arch_hw_breakpoint *info;
 	struct arch_hw_breakpoint_ctrl ctrl;
 
 	slots = this_cpu_ptr(wp_on_reg);
 
+	/*
+	 * Find all watchpoints that match the reported address. If no exact
+	 * match is found. Attribute the hit to the closest watchpoint.
+	 */
+	rcu_read_lock();
 	for (i = 0; i < core_num_wrps; ++i) {
-		rcu_read_lock();
-
 		wp = slots[i];
-
 		if (wp == NULL)
-			goto unlock;
+			continue;
 
-		info = counter_arch_bp(wp);
 		/*
 		 * The DFAR is an unknown value on debug architectures prior
 		 * to 7.1. Since we only allow a single watchpoint on these
@@ -711,50 +753,69 @@ static void watchpoint_handler(unsigned long addr, unsigned int fsr,
 		 */
 		if (debug_arch < ARM_DEBUG_ARCH_V7_1) {
 			BUG_ON(i > 0);
+			info = counter_arch_bp(wp);
 			info->trigger = wp->attr.bp_addr;
 		} else {
-			if (info->ctrl.len == ARM_BREAKPOINT_LEN_8)
-				alignment_mask = 0x7;
-			else
-				alignment_mask = 0x3;
-
-			/* Check if the watchpoint value matches. */
-			val = read_wb_reg(ARM_BASE_WVR + i);
-			if (val != (addr & ~alignment_mask))
-				goto unlock;
-
-			/* Possible match, check the byte address select. */
-			ctrl_reg = read_wb_reg(ARM_BASE_WCR + i);
-			decode_ctrl_reg(ctrl_reg, &ctrl);
-			if (!((1 << (addr & alignment_mask)) & ctrl.len))
-				goto unlock;
-
 			/* Check that the access type matches. */
 			if (debug_exception_updates_fsr()) {
 				access = (fsr & ARM_FSR_ACCESS_MASK) ?
 					  HW_BREAKPOINT_W : HW_BREAKPOINT_R;
 				if (!(access & hw_breakpoint_type(wp)))
-					goto unlock;
+					continue;
+			}
+
+			val = read_wb_reg(ARM_BASE_WVR + i);
+			ctrl_reg = read_wb_reg(ARM_BASE_WCR + i);
+			decode_ctrl_reg(ctrl_reg, &ctrl);
+			dist = get_distance_from_watchpoint(addr, val, &ctrl);
+			if (dist < min_dist) {
+				min_dist = dist;
+				closest_match = i;
 			}
+			/* Is this an exact match? */
+			if (dist != 0)
+				continue;
 
 			/* We have a winner. */
+			info = counter_arch_bp(wp);
 			info->trigger = addr;
 		}
 
 		pr_debug("watchpoint fired: address = 0x%x\n", info->trigger);
+
+		/*
+		 * If we triggered a user watchpoint from a uaccess routine,
+		 * then handle the stepping ourselves since userspace really
+		 * can't help us with this.
+		 */
+		if (watchpoint_fault_on_uaccess(regs, info))
+			goto step;
+
 		perf_bp_event(wp, regs);
 
 		/*
-		 * If no overflow handler is present, insert a temporary
-		 * mismatch breakpoint so we can single-step over the
-		 * watchpoint trigger.
+		 * Defer stepping to the overflow handler if one is installed.
+		 * Otherwise, insert a temporary mismatch breakpoint so that
+		 * we can single-step over the watchpoint trigger.
 		 */
+		if (!is_default_overflow_handler(wp))
+			continue;
+step:
+		enable_single_step(wp, instruction_pointer(regs));
+	}
+
+	if (min_dist > 0 && min_dist != -1) {
+		/* No exact match found. */
+		wp = slots[closest_match];
+		info = counter_arch_bp(wp);
+		info->trigger = addr;
+		pr_debug("watchpoint fired: address = 0x%x\n", info->trigger);
+		perf_bp_event(wp, regs);
 		if (is_default_overflow_handler(wp))
 			enable_single_step(wp, instruction_pointer(regs));
-
-unlock:
-		rcu_read_unlock();
 	}
+
+	rcu_read_unlock();
 }
 
 static void watchpoint_single_step_handler(unsigned long pc)
@@ -825,7 +886,7 @@ static void breakpoint_handler(unsigned long unknown, struct pt_regs *regs)
 			info->trigger = addr;
 			pr_debug("breakpoint fired: address = 0x%x\n", addr);
 			perf_bp_event(bp, regs);
-			if (!bp->overflow_handler)
+			if (is_default_overflow_handler(bp))
 				enable_single_step(bp, addr);
 			goto unlock;
 		}
@@ -867,7 +928,7 @@ static int hw_breakpoint_pending(unsigned long addr, unsigned int fsr,
 		break;
 	case ARM_ENTRY_ASYNC_WATCHPOINT:
 		WARN(1, "Asynchronous watchpoint exception taken. Debugging results may be unreliable\n");
-		/* Fall through */
+		fallthrough;
 	case ARM_ENTRY_SYNC_WATCHPOINT:
 		watchpoint_handler(addr, fsr, regs);
 		break;
@@ -880,6 +941,23 @@ static int hw_breakpoint_pending(unsigned long addr, unsigned int fsr,
 	return ret;
 }
 
+#ifdef CONFIG_ARM_ERRATA_764319
+static int oslsr_fault;
+
+static int debug_oslsr_trap(struct pt_regs *regs, unsigned int instr)
+{
+	oslsr_fault = 1;
+	instruction_pointer(regs) += 4;
+	return 0;
+}
+
+static struct undef_hook debug_oslsr_hook = {
+	.instr_mask  = 0xffffffff,
+	.instr_val = 0xee115e91,
+	.fn = debug_oslsr_trap,
+};
+#endif
+
 /*
  * One-time initialisation.
  */
@@ -913,10 +991,19 @@ static bool core_has_os_save_restore(void)
 	case ARM_DEBUG_ARCH_V7_1:
 		return true;
 	case ARM_DEBUG_ARCH_V7_ECP14:
+#ifdef CONFIG_ARM_ERRATA_764319
+		oslsr_fault = 0;
+		register_undef_hook(&debug_oslsr_hook);
 		ARM_DBG_READ(c1, c1, 4, oslsr);
+		unregister_undef_hook(&debug_oslsr_hook);
+		if (oslsr_fault)
+			return false;
+#else
+		ARM_DBG_READ(c1, c1, 4, oslsr);
+#endif
 		if (oslsr & ARM_OSLSR_OSLM0)
 			return true;
-		/* Else, fall through */
+		fallthrough;
 	default:
 		return false;
 	}