powerpc/watchpoint: Fix length calculation for unaligned target

Watchpoint match range is always doubleword(8 bytes) aligned on
powerpc. If the given range is crossing doubleword boundary, we need
to increase the length such that next doubleword also get
covered. Ex,

          address   len = 6 bytes
                |=========.
   |------------v--|------v--------|
   | | | | | | | | | | | | | | | | |
   |---------------|---------------|
    <---8 bytes--->

In such case, current code configures hw as:
  start_addr = address & ~HW_BREAKPOINT_ALIGN
  len = 8 bytes

And thus read/write in last 4 bytes of the given range is ignored.
Fix this by including next doubleword in the length.
Signed-off-by: Ravi Bangoria <ravi.bangoria@linux.ibm.com>
Signed-off-by: Michael Ellerman <mpe@ellerman.id.au>
Link: https://lore.kernel.org/r/20191017093204.7511-3-ravi.bangoria@linux.ibm.com

arch/powerpc/include/asm/hw_breakpoint.h

@@ -14,6 +14,7 @@ struct arch_hw_breakpoint {
 	unsigned long	address;
 	u16		type;
 	u16		len; /* length of the target data symbol */
+	u16		hw_len; /* length programmed in hw */
 };
 
 /* Note: Don't change the the first 6 bits below as they are in the same order
@@ -73,6 +74,7 @@ static inline void hw_breakpoint_disable(void)
 	brk.address = 0;
 	brk.type = 0;
 	brk.len = 0;
+	brk.hw_len = 0;
 	if (ppc_breakpoint_available())
 		__set_breakpoint(&brk);
 }

arch/powerpc/kernel/dawr.c

@@ -30,10 +30,10 @@ int set_dawr(struct arch_hw_breakpoint *brk)
 	 * DAWR length is stored in field MDR bits 48:53.  Matches range in
 	 * doublewords (64 bits) baised by -1 eg. 0b000000=1DW and
 	 * 0b111111=64DW.
-	 * brk->len is in bytes.
+	 * brk->hw_len is in bytes.
 	 * This aligns up to double word size, shifts and does the bias.
 	 */
-	mrd = ((brk->len + 7) >> 3) - 1;
+	mrd = ((brk->hw_len + 7) >> 3) - 1;
 	dawrx |= (mrd & 0x3f) << (63 - 53);
 
 	if (ppc_md.set_dawr)
@@ -54,7 +54,7 @@ static ssize_t dawr_write_file_bool(struct file *file,
 				    const char __user *user_buf,
 				    size_t count, loff_t *ppos)
 {
-	struct arch_hw_breakpoint null_brk = {0, 0, 0};
+	struct arch_hw_breakpoint null_brk = {0};
 	size_t rc;
 
 	/* Send error to user if they hypervisor won't allow us to write DAWR */

arch/powerpc/kernel/hw_breakpoint.c

@@ -126,6 +126,49 @@ int arch_bp_generic_fields(int type, int *gen_bp_type)
 	return 0;
 }
 
+/*
+ * Watchpoint match range is always doubleword(8 bytes) aligned on
+ * powerpc. If the given range is crossing doubleword boundary, we
+ * need to increase the length such that next doubleword also get
+ * covered. Ex,
+ *
+ *          address   len = 6 bytes
+ *                |=========.
+ *   |------------v--|------v--------|
+ *   | | | | | | | | | | | | | | | | |
+ *   |---------------|---------------|
+ *    <---8 bytes--->
+ *
+ * In this case, we should configure hw as:
+ *   start_addr = address & ~HW_BREAKPOINT_ALIGN
+ *   len = 16 bytes
+ *
+ * @start_addr and @end_addr are inclusive.
+ */
+static int hw_breakpoint_validate_len(struct arch_hw_breakpoint *hw)
+{
+	u16 max_len = DABR_MAX_LEN;
+	u16 hw_len;
+	unsigned long start_addr, end_addr;
+
+	start_addr = hw->address & ~HW_BREAKPOINT_ALIGN;
+	end_addr = (hw->address + hw->len - 1) | HW_BREAKPOINT_ALIGN;
+	hw_len = end_addr - start_addr + 1;
+
+	if (dawr_enabled()) {
+		max_len = DAWR_MAX_LEN;
+		/* DAWR region can't cross 512 bytes boundary */
+		if ((start_addr >> 9) != (end_addr >> 9))
+			return -EINVAL;
+	}
+
+	if (hw_len > max_len)
+		return -EINVAL;
+
+	hw->hw_len = hw_len;
+	return 0;
+}
+
 /*
  * Validate the arch-specific HW Breakpoint register settings
  */
@@ -133,9 +176,9 @@ int hw_breakpoint_arch_parse(struct perf_event *bp,
 			     const struct perf_event_attr *attr,
 			     struct arch_hw_breakpoint *hw)
 {
-	int ret = -EINVAL, length_max;
+	int ret = -EINVAL;
 
-	if (!bp)
+	if (!bp || !attr->bp_len)
 		return ret;
 
 	hw->type = HW_BRK_TYPE_TRANSLATE;
@@ -155,26 +198,10 @@ int hw_breakpoint_arch_parse(struct perf_event *bp,
 	hw->address = attr->bp_addr;
 	hw->len = attr->bp_len;
 
-	/*
-	 * Since breakpoint length can be a maximum of HW_BREAKPOINT_LEN(8)
-	 * and breakpoint addresses are aligned to nearest double-word
-	 * HW_BREAKPOINT_ALIGN by rounding off to the lower address, the
-	 * 'symbolsize' should satisfy the check below.
-	 */
 	if (!ppc_breakpoint_available())
 		return -ENODEV;
-	length_max = DABR_MAX_LEN; /* DABR */
-	if (dawr_enabled()) {
-		length_max = DAWR_MAX_LEN; /* 64 doublewords */
-		/* DAWR region can't cross 512 boundary */
-		if ((attr->bp_addr >> 9) !=
-		    ((attr->bp_addr + attr->bp_len - 1) >> 9))
-			return -EINVAL;
-	}
-	if (hw->len >
-	    (length_max - (hw->address & HW_BREAKPOINT_ALIGN)))
-		return -EINVAL;
-	return 0;
+
+	return hw_breakpoint_validate_len(hw);
 }
 
 /*

arch/powerpc/kernel/process.c

@@ -715,6 +715,8 @@ static void set_debug_reg_defaults(struct thread_struct *thread)
 {
 	thread->hw_brk.address = 0;
 	thread->hw_brk.type = 0;
+	thread->hw_brk.len = 0;
+	thread->hw_brk.hw_len = 0;
 	if (ppc_breakpoint_available())
 		set_breakpoint(&thread->hw_brk);
 }
@@ -816,6 +818,7 @@ static inline bool hw_brk_match(struct arch_hw_breakpoint *a,
 		return false;
 	if (a->len != b->len)
 		return false;
+	/* no need to check hw_len. it's calculated from address and len */
 	return true;
 }
 

arch/powerpc/kernel/ptrace.c

@@ -2426,6 +2426,7 @@ static int ptrace_set_debugreg(struct task_struct *task, unsigned long addr,
 	hw_brk.address = data & (~HW_BRK_TYPE_DABR);
 	hw_brk.type = (data & HW_BRK_TYPE_DABR) | HW_BRK_TYPE_PRIV_ALL;
 	hw_brk.len = DABR_MAX_LEN;
+	hw_brk.hw_len = DABR_MAX_LEN;
 	set_bp = (data) && (hw_brk.type & HW_BRK_TYPE_RDWR);
 #ifdef CONFIG_HAVE_HW_BREAKPOINT
 	bp = thread->ptrace_bps[0];