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 Post subject: [SOLVED] Destroying CPU with microcode update
PostPosted: Thu Aug 05, 2021 8:04 am 
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While browsing the System Programming Guide, Part 1

I am reading this

Attachment:
q.png
q.png [ 64.29 KiB | Viewed 7556 times ]


Is any of you already success to change behavior of some instructions, thus OS crash all the time and the BIOS too.

It's for the science team :twisted:


Last edited by Rukog on Sun Aug 08, 2021 4:53 am, edited 2 times in total.

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 Post subject: Re: Destroying CPU with microcode update
PostPosted: Thu Aug 05, 2021 3:17 pm 
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It's been done.

Of course, that only works if you have a way to load unsigned microcode. AMD added a signature check to their later CPUs, and Intel CPUs have always checked the signature.

There's a hardware exploit that allows bypassing the signature check on some Intel CPUs.


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 Post subject: Re: [SOLVED] Destroying CPU with microcode update
PostPosted: Tue Aug 10, 2021 8:28 am 
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The. title of this thread is rather misleading. A microcode update is not permanent, and is lost on reboot. It can hardly destroy a CPU.


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 Post subject: Re: [SOLVED] Destroying CPU with microcode update
PostPosted: Wed Aug 11, 2021 11:16 am 
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Well, couldn't a microcode update cause a hardware malfunction so catastrophic that the wrong voltages get sent to the CPU, thus destroying it? OK, I admit, that is reaching.

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 Post subject: Re: [SOLVED] Destroying CPU with microcode update
PostPosted: Wed Aug 11, 2021 1:43 pm 
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As far as I am aware the voltages to the CPU are not controlled by the microcode.


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 Post subject: Re: [SOLVED] Destroying CPU with microcode update
PostPosted: Wed Aug 11, 2021 2:58 pm 
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They might be controlled by the firmware's SMM code, which is affected by microcode.

I'd be more concerned about microcode blowing one of the OTP fuses inside the CPU.


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 Post subject: Re: [SOLVED] Destroying CPU with microcode update
PostPosted: Wed Aug 11, 2021 11:32 pm 
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When someone can provide a proof of concept of custom microcode trashing a CPU then I'll believe it's a possibility. If that's what you want to do I would have thought a BIOS modification was a simpler means.


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