MIPS: ptrace: Fix FP context restoration FCSR regression

Fix a floating-point context restoration regression introduced with
commit 9b26616c8d9d ("MIPS: Respect the ISA level in FCSR handling")
that causes a Floating Point exception and consequently a kernel oops
with hard float configurations when one or more FCSR Enable and their
corresponding Cause bits are set both at a time via a ptrace(2) call.

To do so reinstate Cause bit masking originally introduced with commit
b1442d39fac2 ("MIPS: Prevent user from setting FCSR cause bits") to
address this exact problem and then inadvertently removed from the
PTRACE_SETFPREGS request with the commit referred above.

Signed-off-by: Maciej W. Rozycki <macro@imgtec.com>
Cc: stable@vger.kernel.org # v4.0+
Cc: linux-mips@linux-mips.org
Patchwork: https://patchwork.linux-mips.org/patch/13238/
Signed-off-by: Ralf Baechle <ralf@linux-mips.org>

diff --git a/arch/mips/kernel/ptrace.c b/arch/mips/kernel/ptrace.c
index 48c0534c4d15a0128ee1fa1f9580e218a206879a..88a1920669d55158b3f5c4550693ffbfeeeb7531 100644 (file)
--- a/arch/mips/kernel/ptrace.c
+++ b/arch/mips/kernel/ptrace.c
@@ -176,6 +176,7 @@ int ptrace_setfpregs(struct task_struct *child, __u32 __user *data)
        }
 
        __get_user(value, data + 64);
+       value &= ~FPU_CSR_ALL_X;
        fcr31 = child->thread.fpu.fcr31;
        mask = boot_cpu_data.fpu_msk31;
        child->thread.fpu.fcr31 = (value & ~mask) | (fcr31 & mask);