[patch V2 12/52] x86/fpu: Fail ptrace() requests that try to set invalid MXCSR values

[Thomas Gleixner]

From: Andy Lutomirski <luto@xxxxxxxxxx>

We're not doing anyone any favors by accepting and silently changing an
invalid MXCSR value supplied via ptrace().  Instead, return -EINVAL on
invalid input.

If this breaks something, we can revert it.

Signed-off-by: Andy Lutomirski <luto@xxxxxxxxxx>
Signed-off-by: Thomas Gleixner <tglx@xxxxxxxxxxxxx>
---
V2: New patch. Picked up from Andy.
---
 arch/x86/kernel/fpu/regset.c |    5 +++--
 1 file changed, 3 insertions(+), 2 deletions(-)
---
--- a/arch/x86/kernel/fpu/regset.c
+++ b/arch/x86/kernel/fpu/regset.c
@@ -65,8 +65,9 @@ int xfpregs_set(struct task_struct *targ
 	if (ret)
 		return ret;
 
-	/* Mask invalid MXCSR bits (for historical reasons). */
-	newstate.mxcsr &= mxcsr_feature_mask;
+	/* Do not allow an invalid MXCSR value. */
+	if (newstate.mxcsr & ~mxcsr_feature_mask)
+		ret = -EINVAL;
 
 	fpu__prepare_write(fpu);