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Out of interest, do you know if the process of uploading the microcode via the OS independent of the BIOS? ... e.g on something with an unusual boot ROM like a
by tomxor 9y ago
Out of interest, do you know if the process of uploading the microcode via the OS independent of the BIOS? ... e.g on something with an unusual boot ROM like a mac or a Pi (pretend it had an x86) would the kernel not care? i.e it's just a CPU instruction?
- burnte 9y agoYes, it is. OSes protect that ability to prevent malicious microcode, too. The update mechanism is published by Intel, too. Section 9.11 (not page 9.11) https://www.intel.com/content/dam/www/public/us/en/documents/manuals/64-ia-32-architectures-software-developer-vol-3a-part-1-manual.pdf https://www.intel.com/content/dam/www/public/us/en/documents...
- tomxor 9y agoI always assumed that the CPU itself would have an internal signature verification mechanism built in. But after searching it seems the OS or BIOS is responsible for quite a lot... I haven't found anything clearly stating if and where cryptographic signatures are verified. Once source at least suggested that it's only present on >2013 CPUs ! [edit] This is an interesting old paper on x86 microcode security: https://www.dcddcc.com/docs/2014_paper_microcode.pdf https://www.dcddcc.com/docs/2014_paper_microcode.pdf
- AnssiH 9y agoIt should be independent, the Linux x86 microcode code ( https://git.kernel.org/pub/scm/linux/kernel/git/torvalds/linux.git/tree/arch/x86/kernel/cpu/microcode/intel.c https://git.kernel.org/pub/scm/linux/kernel/git/torvalds/lin... and /amd.c) seems to write to MSR (model-specific register) 0x79 on Intel and MSR 0xc0010020 on AMD.