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authorChristian Krinitsin <mail@krinitsin.com>2025-06-16 16:59:00 +0000
committerChristian Krinitsin <mail@krinitsin.com>2025-06-16 16:59:33 +0000
commit9aba81d8eb048db908c94a3c40c25a5fde0caee6 (patch)
treeb765e7fb5e9a3c2143c68b0414e0055adb70e785 /results/classifier/118/network/2951
parentb89a938452613061c0f1f23e710281cf5c83cb29 (diff)
downloadqemu-analysis-9aba81d8eb048db908c94a3c40c25a5fde0caee6.tar.gz
qemu-analysis-9aba81d8eb048db908c94a3c40c25a5fde0caee6.zip
add 18th iteration of classifier
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+network: 0.935
+graphic: 0.840
+device: 0.838
+vnc: 0.799
+peripherals: 0.796
+kernel: 0.768
+performance: 0.755
+socket: 0.693
+files: 0.689
+ppc: 0.666
+architecture: 0.629
+register: 0.614
+hypervisor: 0.583
+boot: 0.561
+risc-v: 0.536
+semantic: 0.529
+permissions: 0.501
+PID: 0.493
+arm: 0.454
+i386: 0.414
+debug: 0.413
+x86: 0.399
+TCG: 0.395
+VMM: 0.379
+user-level: 0.296
+KVM: 0.277
+assembly: 0.249
+mistranslation: 0.142
+virtual: 0.049
+
+First byte of USB NIC is hardcoded to 0x40
+Description of problem:
+Incus recently added support for USB attached network interfaces.
+As with any network device, we generate a MAC address (using our MAC OUI) and allow the user to override that to a value of their choice.
+
+That's when we noticed that no matter what MAC address we set, the resulting MAC always has the prefix swapped to "40:". Looking into the code, this is done on purpose here:
+
+https://gitlab.com/qemu-project/qemu/-/blob/master/hw/usb/dev-network.c?ref_type=heads#L1386
+
+Unfortunately there is no comment in the code or in any of the commits touching that code as far as why that is.
+
+We've also looked at the libvirt code handling those devices and that code seems to also assume that a user provided MAC will be correctly passed through to the guest, no mention of the odd prefix override.
+
+This is a bit concerning as there are valid IEEE OUI with the "40:" prefix.
+So this means that QEMU may be generating collisions with actual physical MAC addresses...
+
+For a few months now, I've been applying this small patch to my own Incus packages (which bundle QEMU) and haven't heard or seen any obvious issue from the change.
+
+https://github.com/zabbly/incus/blob/daily/patches/qemu-0001-usb-net-mac.patch
+
+Does anyone know why this hardcoded MAC address prefix exists?