Windows Client Guidance against speculative execution vulnerabilities

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  1. Posts : 1,561
    Windows 10 Home 20H2 64-bit
       #690

    Kbird said:
    Same Issue with Asus X99 Series , it is suggested that X99 is EOL or beyond Warranty as the reason for this on TechpowerUp , however my X99 is not even two years old yet.....

    ASUS Begins Rolling Out 9-series Chipset Spectre/Meltdown Hardening BIOS Updates | TechPowerUp
    Ah, so that beta label doesn't actually mean that it's an unfinished BIOS update but more as a warning if something bad happens it's not covered in the warranty by the manufacturer because the product is EOL? That makes sense… Sort of. Seeing that there are even more Spectre Variants just discovered I'm still going to wait before updating.
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  2. Posts : 345
    Windows 10
       #691

    fdegrove said:
    Hi,



    Was wondering about that too. Seems like every new version of W10 is like a new OS all on its own....
    After all, this is only a MC emulation, right ?

    Cheers,

    I don't know. I'm still unable to find a source that states that Windows doesn't copy the microcode update to volatile memory on the CPU and instead runs some sort of emulation.
    Last edited by Ground Sloth; 06 May 2018 at 21:26.
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  3. Posts : 61,465
    64-bit Windows 11 Pro for Workstations
    Thread Starter
       #692

    Microsoft updated article in first post on May 17, 2018.
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  4. Posts : 24,475
    10 Home x64 (21H2) (10 Pro on 2nd pc)
       #693

    Ground Sloth said:
    I don't know. I'm still unable to find a source that states that Windows doesn't copy the microcode update to volatile memory on the CPU and instead runs some sort of emulation.
    This paper makes it clear that the update mechanism and the end result is the same whether delivered by the bios, Windows drivers or Linux. The microcode is written to the cpu.

    ...Although this microcode was initially implemented on read-only memory, processor manufacturers soon introduced writable patch memory to provide an update mechanism...
    ...
    4.2 Update Mechanism
    The microcode update mechanism is very similar across all x86 processor manufacturers, primarily by using processor model-specific register (MSR) registers to read the current microcode revision and write the new microcode update...
    ...
    4.3.2 Windows
    Although less well documented, microcode updates are performed by bundled device drivers on Windows XP and later. Unlike the Linux update module, these Windows drivers have binary microcode updates integrated within the segments, and cannot load microcode from manufacturer-supplied update packages...
    https://www.dcddcc.com/docs/2014_paper_microcode.pdf
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  5. Posts : 345
    Windows 10
       #694

    Bree said:
    This paper makes it clear that the update mechanism and the end result is the same whether delivered by the bios, Windows drivers or Linux. The microcode is written to the cpu.

    https://www.dcddcc.com/docs/2014_paper_microcode.pdf

    That's what I've been saying for a couple months now. More specifically, the microcode update is written to volatile memory on the CPU and is thus not persistent across reboots.
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  6. Posts : 24,475
    10 Home x64 (21H2) (10 Pro on 2nd pc)
       #695

    Ground Sloth said:
    More specifically, the microcode update is written to volatile memory on the CPU and is thus not persistent across reboots.
    I fail to see a problem with that. Once loaded its a permanent part of the cpu until you power down. Then it loads again from (preferably) the bios at next power up.

    That's the mechanism all the CPU manufacturers have chosen to use. You'd prefer it to be read-only, as it initially was in the '70s? Or EEPROM/flash (like legacy bios chips) with a limited number of erase/write cycles?
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  7. Posts : 345
    Windows 10
       #696

    Bree said:
    I fail to see a problem with that. Once loaded its a permanent part of the cpu until you power down. Then it loads again from (preferably) the bios at next power up.

    That's the mechanism all the CPU manufacturers have chosen to use. You'd prefer it to be read-only, as it initially was in the '70s? Or EEPROM/flash (like legacy bios chips) with a limited number of erase/write cycles?

    I never said it was problematic.

    I've been saying for a couple months that regardless if the BIOS or Windows updates the CPU microcode, the microcode update is written to volatile memory on the CPU. But some other forum members have told me that I'm wrong.
    Last edited by Ground Sloth; 19 May 2018 at 00:03.
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  8. Posts : 1,439
    Windows 10 Pro 64bit 20H2 19042.844
       #697

    Heres Mine after Bios Update this Morning on my Asus G11CD-K Desktop
    Attached Thumbnails Attached Thumbnails Windows Client Guidance against speculative execution vulnerabilities-spectre.jpg  
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  9. Posts : 24,475
    10 Home x64 (21H2) (10 Pro on 2nd pc)
       #698

    Ground Sloth said:
    I've been saying for a couple months that regardless if the BIOS or Windows updates the CPU microcode, the microcode update is written to volatile memory on the CPU. But some other forum members have told me that I'm wrong.
    No argument with you there @Ground Sloth, we are in total agreement. BIOS or Windows, the same microcode gets written to the CPU either way.

    Some seem to have got the idea that the update isn't a 'proper' solution, that it is some sort of software 'simulation' or 'emulation' running in conventional memory - they are mistaken.
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  10. Posts : 2,826
    Windows 10 Pro X64
       #699

    Hi,

    I've been saying for a couple months that regardless if the BIOS or Windows updates the CPU microcode, the microcode update is written to volatile memory on the CPU. But some other forum members have told me that I'm wrong.
    Bios/UEFI flash update is persistent and is not written to volatile memory on the cpu.
    As far as mitigation against Spectre type attacks is concerned it really makes no difference whether the OS tells itself it is reading the MC it is told to read resides inside the CPU or it fools itself reading it from what? L3 CPU cache ?
    I somewhat doubt it would cache it to L3 CPU volatile cache as any volatile memory would do but it really does not matter.

    Point is, both methods are safe and yes BIOS/UEFI flash is persistent whereas OS MCU is not but the end result is the same securitywise.

    To me emulation is like "make believe". All OS's do it and so on. Anyway, just semantics really.

    Cheers,
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