How to hide the SSE2 CPU flag for Windows OS

[reboot12]

In QEMU (virt-manager) on Linux you have to do this:

qemu-system-x86_64 -cpu host,-sse2

In QEMU on Windows:

qemu-system-x86_64 -cpu qemu64,-sse2

In the Linux host system, e.g. Debian you need add the option clearcpuid=26 to the kernel cmd line in /etc/default/grub:

GRUB_CMDLINE_LINUX="clearcpuid=26"

then update-grub and reboot

To check if it works:

cat /proc/cpuinfo | grep flags

How to disable CPU Feature / Flag HLE "Hardware Lock Elision" on RHEL x86 - intel

cpufeatures.h

#define X86_FEATURE_XMM2 ( 0*32+26) /* "sse2" */

How to achieve the same for Windows without using a virtual machine?

I found it: set-sse2-enable but this is a guide on how to compile their own applications so that they do not use SSE2

sse2_use_not_use.zip - test tools fo Win 32-bit

Edited January 29, 2023 by reboot12

[reboot12]

Maybe it can be done from the GRU4DOS ???

[Mov AX, 0xDEAD]

For Windows sse2 is same like sse1, if you don't want sse2, disable sse too.

There is no switch for windows kernel to disable sse, you need modded kernel, do it yourself

[reboot12]

1 hour ago, Mov AX, 0xDEAD said:

There is no switch for windows kernel to disable sse, you need modded kernel, do it yourself

There is no for Windows but it is in Grub2 - WRMSR command I just don't know what registry address to change the bit 26 SSE2:

I also found a msr-cmd.exe tool for Windows but I don't know how to use it to edit bit 26 SSE2:

Usage:
        msr-cmd.exe [options] read <reg>
        msr-cmd.exe [options] write <reg> <edx(63~32)> <eax(31~0)>
        msr-cmd.exe [options] -l write <reg> <hex_val(63~0)>
        msr-cmd.exe [options] rmw <reg> <h bit> <l bit> <unmasked_hex_val>
        msr-cmd.exe [options] rmwmask <reg> <mask(63~0)> <unmasked_hex_val>
        msr-cmd.exe [options] getbit <reg> <#bit>
        msr-cmd.exe [options] setbit <reg> <#bit> <0/1>

Options:
        -s              write only do not read back
        -d              data only, not to print column item name
        -g <GRP>        processor group (default: 0) to apply
                        'A' or 'a' to apply to all available processors groups
                        by default, a group can contain up to 64 logical processors

However, I modified another - IA32_CLOCK_MODULATION 0x19A register without any problems in GRUB2:

wrmsr 0x19a 0x12

or under WinXP 64-bit with msr-cmd.exe:

msr-cmd read 0x19a
msr_read(): CPU 0 reg: 0x0000019a edx: 0x00000000 eax: 0x00000002
msr-cmd write 0x19a 0x00000000 0x00000012
msr_write(): ret: CPU 0 reg: 0x0000019a edx: 0x00000000 eax: 0x00000012

Edited August 17, 2023 by reboot12

[Mov AX, 0xDEAD]

17 hours ago, reboot12 said:

I also found a msr-cmd.exe tool for Windows but I don't know how to use it to edit bit 26 SSE2:

Look at intel or amd CPU Programming documentation how to control SSE bit in MSR registers, "Internet" says some old BIOS have "SSE Enable/Disable" option, so it must be possible

 

[reboot12]

14 hours ago, Mov AX, 0xDEAD said:

"Internet" says some old BIOS have "SSE Enable/Disable" option, so it must be possible

Yes, you are right - I found and, for example, in the BIOS JetWay V266B there was such an option:

[reboot12]

I found interesting tool for change CPUID Name from Windows 32-bit - tested WinXP SP2: amdp4_test.zip

I modified my own name in the hex editor :-)

Can someone change the source code msr_test.exe to modify the SSE2 CPUID?