ghsa-43j5-9vgx-7g7j
Vulnerability from github
In the Linux kernel, the following vulnerability has been resolved:
x86/coco: Require seeding RNG with RDRAND on CoCo systems
There are few uses of CoCo that don't rely on working cryptography and hence a working RNG. Unfortunately, the CoCo threat model means that the VM host cannot be trusted and may actively work against guests to extract secrets or manipulate computation. Since a malicious host can modify or observe nearly all inputs to guests, the only remaining source of entropy for CoCo guests is RDRAND.
If RDRAND is broken -- due to CPU hardware fault -- the RNG as a whole is meant to gracefully continue on gathering entropy from other sources, but since there aren't other sources on CoCo, this is catastrophic. This is mostly a concern at boot time when initially seeding the RNG, as after that the consequences of a broken RDRAND are much more theoretical.
So, try at boot to seed the RNG using 256 bits of RDRAND output. If this fails, panic(). This will also trigger if the system is booted without RDRAND, as RDRAND is essential for a safe CoCo boot.
Add this deliberately to be "just a CoCo x86 driver feature" and not part of the RNG itself. Many device drivers and platforms have some desire to contribute something to the RNG, and add_device_randomness() is specifically meant for this purpose.
Any driver can call it with seed data of any quality, or even garbage quality, and it can only possibly make the quality of the RNG better or have no effect, but can never make it worse.
Rather than trying to build something into the core of the RNG, consider the particular CoCo issue just a CoCo issue, and therefore separate it all out into driver (well, arch/platform) code.
[ bp: Massage commit message. ]
{
"affected": [],
"aliases": [
"CVE-2024-35875"
],
"database_specific": {
"cwe_ids": [],
"github_reviewed": false,
"github_reviewed_at": null,
"nvd_published_at": "2024-05-19T09:15:08Z",
"severity": null
},
"details": "In the Linux kernel, the following vulnerability has been resolved:\n\nx86/coco: Require seeding RNG with RDRAND on CoCo systems\n\nThere are few uses of CoCo that don\u0027t rely on working cryptography and\nhence a working RNG. Unfortunately, the CoCo threat model means that the\nVM host cannot be trusted and may actively work against guests to\nextract secrets or manipulate computation. Since a malicious host can\nmodify or observe nearly all inputs to guests, the only remaining source\nof entropy for CoCo guests is RDRAND.\n\nIf RDRAND is broken -- due to CPU hardware fault -- the RNG as a whole\nis meant to gracefully continue on gathering entropy from other sources,\nbut since there aren\u0027t other sources on CoCo, this is catastrophic.\nThis is mostly a concern at boot time when initially seeding the RNG, as\nafter that the consequences of a broken RDRAND are much more\ntheoretical.\n\nSo, try at boot to seed the RNG using 256 bits of RDRAND output. If this\nfails, panic(). This will also trigger if the system is booted without\nRDRAND, as RDRAND is essential for a safe CoCo boot.\n\nAdd this deliberately to be \"just a CoCo x86 driver feature\" and not\npart of the RNG itself. Many device drivers and platforms have some\ndesire to contribute something to the RNG, and add_device_randomness()\nis specifically meant for this purpose.\n\nAny driver can call it with seed data of any quality, or even garbage\nquality, and it can only possibly make the quality of the RNG better or\nhave no effect, but can never make it worse.\n\nRather than trying to build something into the core of the RNG, consider\nthe particular CoCo issue just a CoCo issue, and therefore separate it\nall out into driver (well, arch/platform) code.\n\n [ bp: Massage commit message. ]",
"id": "GHSA-43j5-9vgx-7g7j",
"modified": "2024-05-19T09:34:46Z",
"published": "2024-05-19T09:34:46Z",
"references": [
{
"type": "ADVISORY",
"url": "https://nvd.nist.gov/vuln/detail/CVE-2024-35875"
},
{
"type": "WEB",
"url": "https://git.kernel.org/stable/c/08044b08b37528b82f70a87576c692b4e4b7716e"
},
{
"type": "WEB",
"url": "https://git.kernel.org/stable/c/22943e4fe4b3a2dcbadc3d38d5bf840bbdbfe374"
},
{
"type": "WEB",
"url": "https://git.kernel.org/stable/c/453b5f2dec276c1bb4ea078bf8c0da57ee4627e5"
},
{
"type": "WEB",
"url": "https://git.kernel.org/stable/c/99485c4c026f024e7cb82da84c7951dbe3deb584"
}
],
"schema_version": "1.4.0",
"severity": []
}
- Seen: The vulnerability was mentioned, discussed, or seen somewhere by the user.
- Confirmed: The vulnerability is confirmed from an analyst perspective.
- Exploited: This vulnerability was exploited and seen by the user reporting the sighting.
- Patched: This vulnerability was successfully patched by the user reporting the sighting.
- Not exploited: This vulnerability was not exploited or seen by the user reporting the sighting.
- Not confirmed: The user expresses doubt about the veracity of the vulnerability.
- Not patched: This vulnerability was not successfully patched by the user reporting the sighting.