powerpc/watchpoint: Fix ptrace code that muck around with address/len

ptrace_set_debugreg() does not consider new length while overwriting
the watchpoint. Fix that. ppc_set_hwdebug() aligns watchpoint address
to doubleword boundary but does not change the length. If address
range is crossing doubleword boundary and length is less then 8, we
will lose samples from second doubleword. So fix that as well.
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/20191017093204.7511-4-ravi.bangoria@linux.ibm.com

arch/powerpc/include/asm/hw_breakpoint.h

@@ -34,6 +34,8 @@ struct arch_hw_breakpoint {
 #define HW_BRK_TYPE_PRIV_ALL	(HW_BRK_TYPE_USER | HW_BRK_TYPE_KERNEL | \
 				 HW_BRK_TYPE_HYP)
 
+#define HW_BREAKPOINT_ALIGN 0x7
+
 #define DABR_MAX_LEN	8
 #define DAWR_MAX_LEN	512
 
@@ -48,8 +50,6 @@ struct pmu;
 struct perf_sample_data;
 struct task_struct;
 
-#define HW_BREAKPOINT_ALIGN 0x7
-
 extern int hw_breakpoint_slots(int type);
 extern int arch_bp_generic_fields(int type, int *gen_bp_type);
 extern int arch_check_bp_in_kernelspace(struct arch_hw_breakpoint *hw);

arch/powerpc/kernel/ptrace.c

@@ -2440,6 +2440,7 @@ static int ptrace_set_debugreg(struct task_struct *task, unsigned long addr,
 	if (bp) {
 		attr = bp->attr;
 		attr.bp_addr = hw_brk.address;
+		attr.bp_len = DABR_MAX_LEN;
 		arch_bp_generic_fields(hw_brk.type, &attr.bp_type);
 
 		/* Enable breakpoint */
@@ -2881,7 +2882,7 @@ static long ppc_set_hwdebug(struct task_struct *child,
 	if ((unsigned long)bp_info->addr >= TASK_SIZE)
 		return -EIO;
 
-	brk.address = bp_info->addr & ~7UL;
+	brk.address = bp_info->addr & ~HW_BREAKPOINT_ALIGN;
 	brk.type = HW_BRK_TYPE_TRANSLATE;
 	brk.len = DABR_MAX_LEN;
 	if (bp_info->trigger_type & PPC_BREAKPOINT_TRIGGER_READ)
@@ -2889,10 +2890,6 @@ static long ppc_set_hwdebug(struct task_struct *child,
 	if (bp_info->trigger_type & PPC_BREAKPOINT_TRIGGER_WRITE)
 		brk.type |= HW_BRK_TYPE_WRITE;
 #ifdef CONFIG_HAVE_HW_BREAKPOINT
-	/*
-	 * Check if the request is for 'range' breakpoints. We can
-	 * support it if range < 8 bytes.
-	 */
 	if (bp_info->addr_mode == PPC_BREAKPOINT_MODE_RANGE_INCLUSIVE)
 		len = bp_info->addr2 - bp_info->addr;
 	else if (bp_info->addr_mode == PPC_BREAKPOINT_MODE_EXACT)
@@ -2905,7 +2902,7 @@ static long ppc_set_hwdebug(struct task_struct *child,
 
 	/* Create a new breakpoint request if one doesn't exist already */
 	hw_breakpoint_init(&attr);
-	attr.bp_addr = (unsigned long)bp_info->addr & ~HW_BREAKPOINT_ALIGN;
+	attr.bp_addr = (unsigned long)bp_info->addr;
 	attr.bp_len = len;
 	arch_bp_generic_fields(brk.type, &attr.bp_type);