x86/MSR: Filter MSR writes through X86_IOC_WRMSR_REGS ioctl too

Commit

  a7e1f67e ("x86/msr: Filter MSR writes")

introduced a module parameter to disable writing to the MSR device file
and tainted the kernel upon writing. As MSR registers can be written by
the X86_IOC_WRMSR_REGS ioctl too, the same filtering and tainting should
be applied to the ioctl as well.

 [ bp: Massage commit message and space out statements. ]

Fixes: a7e1f67e ("x86/msr: Filter MSR writes")
Signed-off-by: Misono Tomohiro <misono.tomohiro@jp.fujitsu.com>
Signed-off-by: Borislav Petkov <bp@suse.de>
Link: https://lkml.kernel.org/r/20210127122456.13939-1-misono.tomohiro@jp.fujitsu.com

arch/x86/kernel/msr.c

@@ -182,6 +182,13 @@ static long msr_ioctl(struct file *file, unsigned int ioc, unsigned long arg)
 		err = security_locked_down(LOCKDOWN_MSR);
 		if (err)
 			break;
+
+		err = filter_write(regs[1]);
+		if (err)
+			return err;
+
+		add_taint(TAINT_CPU_OUT_OF_SPEC, LOCKDEP_STILL_OK);
+
 		err = wrmsr_safe_regs_on_cpu(cpu, regs);
 		if (err)
 			break;