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>

1 files changed, 21 insertions, 16 deletions

diff --git a/arch/arm64/kernel/ptrace.c b/arch/arm64/kernel/ptrace.c
index c62d39d5c99f..6e1e77f1831c 100644
--- 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;
 }