arm64: ptrace: use HW_BREAKPOINT_EMPTY type for disabled breakpoints

If a debugger tries to zero a hardware debug control register, the
kernel will try to infer both the type and length of the breakpoint
in order to sanity-check against the requested regset type. This will
fail because the encoding will appear as a zero-length breakpoint.

This patch changes the control register setting so that disabled
breakpoints are treated as HW_BREAKPOINT_EMPTY and no further
sanity-checking is required.

Signed-off-by: Will Deacon <will.deacon@arm.com>
Signed-off-by: Catalin Marinas <catalin.marinas@arm.com>

diff --git a/arch/arm64/kernel/ptrace.c b/arch/arm64/kernel/ptrace.c
index c62d39d5c99f353d0050c3b4d7fbd2512f14bf5d..6e1e77f1831c0cb0bf31306822ebc72ba8d3158a 100644 (file)
--- a/arch/arm64/kernel/ptrace.c
+++ b/arch/arm64/kernel/ptrace.c
@@ -234,28 +234,33 @@ static int ptrace_hbp_fill_attr_ctrl(unsigned int note_type,
                                     struct arch_hw_breakpoint_ctrl ctrl,
                                     struct perf_event_attr *attr)
 {
-       int err, len, type;
+       int err, len, type, disabled = !ctrl.enabled;
 
-       err = arch_bp_generic_fields(ctrl, &len, &type);
-       if (err)
-               return err;
-
-       switch (note_type) {
-       case NT_ARM_HW_BREAK:
-               if ((type & HW_BREAKPOINT_X) != type)
-                       return -EINVAL;
-               break;
-       case NT_ARM_HW_WATCH:
-               if ((type & HW_BREAKPOINT_RW) != type)
+       if (disabled) {
+               len = 0;
+               type = HW_BREAKPOINT_EMPTY;
+       } else {
+               err = arch_bp_generic_fields(ctrl, &len, &type);
+               if (err)
+                       return err;
+
+               switch (note_type) {
+               case NT_ARM_HW_BREAK:
+                       if ((type & HW_BREAKPOINT_X) != type)
+                               return -EINVAL;
+                       break;
+               case NT_ARM_HW_WATCH:
+                       if ((type & HW_BREAKPOINT_RW) != type)
+                               return -EINVAL;
+                       break;
+               default:
                        return -EINVAL;
-               break;
-       default:
-               return -EINVAL;
+               }
        }
 
        attr->bp_len    = len;
        attr->bp_type   = type;
-       attr->disabled  = !ctrl.enabled;
+       attr->disabled  = disabled;
 
        return 0;
 }