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

Thomas Gleixner
2021-06-14T16:38:35Z

From: Andy Lutomirski <luto@kernel.org>

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@kernel.org>
Signed-off-by: Thomas Gleixner <tglx@linutronix.de>
---
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);