x86_64: ia32 ptrace THREAD_AREA fix

The addr argument to PTRACE_GET_THREAD_AREA and PTRACE_SET_THREAD_AREA is
not a magic constant. It's derived from the segment register values being
used, which are computed originally from the index used with set_thread_area.
The value does not need to match what a native i386 kernel would accept.
It needs to match the segment selectors that can actually be in use in this
32-bit process. The 64-bit ptrace support for PTRACE_GET_THREAD_AREA
(normally used only on 32-bit processes) is correct, but the 32-bit emulation
of ptrace is broken.

Signed-off-by: Roland McGrath <[e-mail]>
Signed-off-by: Thomas Gleixner <[e-mail]>

arch/x86/ia32/ptrace32.c

···
 	return ret;
 }
 
-#define COMPAT_GDT_ENTRY_TLS_MIN 6
-
 asmlinkage long sys32_ptrace(long request, u32 pid, u32 addr, u32 data)
 {
 	struct task_struct *child;
···
 	case PTRACE_SYSCALL:
 	case PTRACE_OLDSETOPTIONS:
 	case PTRACE_SETOPTIONS:
+	case PTRACE_SET_THREAD_AREA:
+	case PTRACE_GET_THREAD_AREA:
 		return sys_ptrace(request, pid, addr, data); 
 
 	default:
···
 	case PTRACE_SETSIGINFO:
 	case PTRACE_GETSIGINFO:
 		return ptrace32_siginfo(request, pid, addr, data);
-
-	case PTRACE_SET_THREAD_AREA:
-	case PTRACE_GET_THREAD_AREA:
-		return sys_ptrace(request, pid,
-			addr + GDT_ENTRY_TLS_MIN - COMPAT_GDT_ENTRY_TLS_MIN,
-			data);
 	}
 
 	child = ptrace_get_task_struct(pid);