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

Borislav Petkov
2021-06-16T15:31:46Z

On Mon, Jun 14, 2021 at 05:44:20PM +0200, Thomas Gleixner wrote:
> 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.

Please use passive voice in your commit message: no "we" or "I", etc,

> 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);

With that addressed:

Reviewed-by: Borislav Petkov <bp@suse.de>

Thx.

--
Regards/Gruss,
Boris.

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