MIPS: ptrace: Fix PTRACE_PEEKUSR requests for 64-bit FGRs

BugLink: https://bugs.launchpad.net/bugs/1776177

commit c7e81462 upstream.

Use 64-bit accesses for 64-bit floating-point general registers with
PTRACE_PEEKUSR, removing the truncation of their upper halves in the
FR=1 mode, caused by commit bbd426f5 ("MIPS: Simplify FP context
access"), which inadvertently switched them to using 32-bit accesses.

The PTRACE_POKEUSR side is fine as it's never been broken and continues
using 64-bit accesses.

Fixes: bbd426f5 ("MIPS: Simplify FP context access")
Signed-off-by: Maciej W. Rozycki <macro@mips.com>
Cc: Ralf Baechle <ralf@linux-mips.org>
Cc: linux-mips@linux-mips.org
Cc: <stable@vger.kernel.org> # 3.15+
Patchwork: https://patchwork.linux-mips.org/patch/19334/Signed-off-by: James Hogan <jhogan@kernel.org>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
Signed-off-by: Juerg Haefliger <juergh@canonical.com>
Signed-off-by: Khalid Elmously <khalid.elmously@canonical.com>

arch/mips/kernel/ptrace.c

@@ -841,7 +841,7 @@ long arch_ptrace(struct task_struct *child, long request,
 				break;
 			}
 #endif
-			tmp = get_fpr32(&fregs[addr - FPR_BASE], 0);
+			tmp = get_fpr64(&fregs[addr - FPR_BASE], 0);
 			break;
 		case PC:
 			tmp = regs->cp0_epc;

arch/mips/kernel/ptrace32.c

@@ -107,7 +107,7 @@ long compat_arch_ptrace(struct task_struct *child, compat_long_t request,
 						addr & 1);
 				break;
 			}
-			tmp = get_fpr32(&fregs[addr - FPR_BASE], 0);
+			tmp = get_fpr64(&fregs[addr - FPR_BASE], 0);
 			break;
 		case PC:
 			tmp = regs->cp0_epc;