[PATCH 4.6 021/121] MIPS: ptrace: Fix FP context restoration FCSR regression

From: Greg Kroah-Hartman
Date: Sun Jun 05 2016 - 18:21:05 EST

4.6-stable review patch. If anyone has any objections, please let me know.


From: Maciej W. Rozycki <macro@xxxxxxxxxx>

commit 4249548454f7ba4581aeee26bd83f42b48a14d15 upstream.

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@xxxxxxxxxx>
Cc: linux-mips@xxxxxxxxxxxxxx
Patchwork: https://patchwork.linux-mips.org/patch/13238/
Signed-off-by: Ralf Baechle <ralf@xxxxxxxxxxxxxx>
Signed-off-by: Greg Kroah-Hartman <gregkh@xxxxxxxxxxxxxxxxxxx>

arch/mips/kernel/ptrace.c | 1 +
1 file changed, 1 insertion(+)

--- a/arch/mips/kernel/ptrace.c
+++ b/arch/mips/kernel/ptrace.c
@@ -176,6 +176,7 @@ int ptrace_setfpregs(struct task_struct

__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);