[tip: x86/misc] x86/MSR: Filter MSR writes through X86_IOC_WRMSR_REGS ioctl too

[tip-bot2 for Misono Tomohiro]

The following commit has been merged into the x86/misc branch of tip:

Commit-ID:     02a16aa13574c8526beadfc9ae8cc9b66315fa2d
Gitweb:        https://git.kernel.org/tip/02a16aa13574c8526beadfc9ae8cc9b66315fa2d
Author:        Misono Tomohiro <misono.tomohiro@xxxxxxxxxxxxxx>
AuthorDate:    Wed, 27 Jan 2021 21:24:56 +09:00
Committer:     Borislav Petkov <bp@xxxxxxx>
CommitterDate: Wed, 27 Jan 2021 19:06:47 +01:00

x86/MSR: Filter MSR writes through X86_IOC_WRMSR_REGS ioctl too

Commit

  a7e1f67ed29f ("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: a7e1f67ed29f ("x86/msr: Filter MSR writes")
Signed-off-by: Misono Tomohiro <misono.tomohiro@xxxxxxxxxxxxxx>
Signed-off-by: Borislav Petkov <bp@xxxxxxx>
Link: https://lkml.kernel.org/r/20210127122456.13939-1-misono.tomohiro@xxxxxxxxxxxxxx
---
 arch/x86/kernel/msr.c | 7 +++++++
 1 file changed, 7 insertions(+)

diff --git a/arch/x86/kernel/msr.c b/arch/x86/kernel/msr.c
index 8a67d1f..ed8ac6b 100644
--- a/arch/x86/kernel/msr.c
+++ b/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;