Kernel does not appear to recognise NX CPU flag

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Kernel does not appear to recognise NX CPU flag

Post by Ghepardo » 2020/10/16 15:40:49

I am trying to harden a CentOS 7.6 VM. The kernel does not appear to recognise the NX CPU flag.

The system: Running on a VMware host with Intel Xeon CPUs. The VM is configured to 'Expose the NX/XD flag to guest'. I do indeed see it on the guest CPUs: /proc/cpuinfo shows 'nx' amongst the flags.

The issue: I understand that the dmesg output should show a line containing "NX (Execute Disable) protection: active". There is no such line. I have also checked /var/log/messages and 'journalctl -b'. I have also checked for "XD" and "protection". All fail to show anything. And /proc/cmdline does not contain a "noexec" setting.

From Googling, I understand that there is no longer a kernel parameter to control this, but that support for NX is enabled by default if the CPU supports it. What am I doing wrong here, in failing to find it in dmesg?

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Re: Kernel does not appear to recognise NX CPU flag

Post by BShT » 2020/10/16 17:50:44

look at BIOS

and update your Centos

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Re: Kernel does not appear to recognise NX CPU flag

Post by TrevorH » 2020/10/16 18:38:35

It'll also be listed in /proc/cpuinfo in the flags line which should contain " nx " if it's supported. If it does not list it then I would think this is a VMWare problem not passing it through to the guest. Did you do a virtual power cycle of the VM after changing the VMWare settings to enable it?

And CentOS 7.6 is 2 whole point release behind the current version, soon to be 3 as 7.9 is being built and tested as I type. Your system is out of date, has several high severity security vulnerabilities and needs to be updated using yum update as your system is currently more than 2 years out of date.
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