linux-kernel - [PATCH] x86/msr: Filter msr write by X86_IOC_WRMSR

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Date:   Wed, 27 Jan 2021 21:24:56 +0900
From:   Misono Tomohiro <misono.tomohiro@...fujitsu.com>
To:     <linux-kernel@...r.kernel.org>
CC:     <x86@...nel.org>, <hpa@...or.com>, <tglx@...utronix.de>,
        <mingo@...hat.com>, <bp@...en8.de>,
        <misono.tomohiro@...fujitsu.com>
Subject: [PATCH] x86/msr: Filter msr write by X86_IOC_WRMSR_REGS ioctl

commit a7e1f67ed29f ("x86/msr: Filter MSR writes") introduces a
module parameter to disable writing to msr device file (and add_taint()
upon writing). As msr register can be written by X86_IOC_WRMSR_REGS
ioctl too, they should be applied to the ioctl as well.

Fixes: a7e1f67ed29f ("x86/msr: Filter MSR writes")
Signed-off-by: Misono Tomohiro <misono.tomohiro@...fujitsu.com>
---
Hello,

I just noticed this when I read the code.
I'm not sure if anyone uses ioctl interface now, but I tested this
by resetting IA32_MPERF by X86_IOC_WRMSR_REGS ioctl.

Thanks,

 arch/x86/kernel/msr.c | 4 ++++
 1 file changed, 4 insertions(+)

diff --git a/arch/x86/kernel/msr.c b/arch/x86/kernel/msr.c
index 8a67d1fa8dc5..d774618e75b8 100644
--- a/arch/x86/kernel/msr.c
+++ b/arch/x86/kernel/msr.c
@@ -182,6 +182,10 @@ 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;
-- 
2.26.2