ghsa-gg7f-9mpf-7m5f
Vulnerability from github
In the Linux kernel, the following vulnerability has been resolved:
ARM: 9063/1: mm: reduce maximum number of CPUs if DEBUG_KMAP_LOCAL is enabled
The debugging code for kmap_local() doubles the number of per-CPU fixmap slots allocated for kmap_local(), in order to use half of them as guard regions. This causes the fixmap region to grow downwards beyond the start of its reserved window if the supported number of CPUs is large, and collide with the newly added virtual DT mapping right below it, which is obviously not good.
One manifestation of this is EFI boot on a kernel built with NR_CPUS=32 and CONFIG_DEBUG_KMAP_LOCAL=y, which may pass the FDT in highmem, resulting in block entries below the fixmap region that the fixmap code misidentifies as fixmap table entries, and subsequently tries to dereference using a phys-to-virt translation that is only valid for lowmem. This results in a cryptic splat such as the one below.
ftrace: allocating 45548 entries in 89 pages
8<--- cut here ---
Unable to handle kernel paging request at virtual address fc6006f0
pgd = (ptrval)
[fc6006f0] pgd=80000040207003, pmd=00000000
Internal error: Oops: a06 [#1] SMP ARM
Modules linked in:
CPU: 0 PID: 0 Comm: swapper Not tainted 5.11.0+ #382
Hardware name: Generic DT based system
PC is at cpu_ca15_set_pte_ext+0x24/0x30
LR is at __set_fixmap+0xe4/0x118
pc : [
So let's limit CONFIG_NR_CPUS to 16 when CONFIG_DEBUG_KMAP_LOCAL=y. Also, fix the BUILD_BUG_ON() check that was supposed to catch this, by checking whether the region grows below the start address rather than above the end address.
{
"affected": [],
"aliases": [
"CVE-2021-46910"
],
"database_specific": {
"cwe_ids": [],
"github_reviewed": false,
"github_reviewed_at": null,
"nvd_published_at": "2024-02-27T07:15:07Z",
"severity": "MODERATE"
},
"details": "In the Linux kernel, the following vulnerability has been resolved:\n\nARM: 9063/1: mm: reduce maximum number of CPUs if DEBUG_KMAP_LOCAL is enabled\n\nThe debugging code for kmap_local() doubles the number of per-CPU fixmap\nslots allocated for kmap_local(), in order to use half of them as guard\nregions. This causes the fixmap region to grow downwards beyond the start\nof its reserved window if the supported number of CPUs is large, and collide\nwith the newly added virtual DT mapping right below it, which is obviously\nnot good.\n\nOne manifestation of this is EFI boot on a kernel built with NR_CPUS=32\nand CONFIG_DEBUG_KMAP_LOCAL=y, which may pass the FDT in highmem, resulting\nin block entries below the fixmap region that the fixmap code misidentifies\nas fixmap table entries, and subsequently tries to dereference using a\nphys-to-virt translation that is only valid for lowmem. This results in a\ncryptic splat such as the one below.\n\n ftrace: allocating 45548 entries in 89 pages\n 8\u003c--- cut here ---\n Unable to handle kernel paging request at virtual address fc6006f0\n pgd = (ptrval)\n [fc6006f0] *pgd=80000040207003, *pmd=00000000\n Internal error: Oops: a06 [#1] SMP ARM\n Modules linked in:\n CPU: 0 PID: 0 Comm: swapper Not tainted 5.11.0+ #382\n Hardware name: Generic DT based system\n PC is at cpu_ca15_set_pte_ext+0x24/0x30\n LR is at __set_fixmap+0xe4/0x118\n pc : [\u003cc041ac9c\u003e] lr : [\u003cc04189d8\u003e] psr: 400000d3\n sp : c1601ed8 ip : 00400000 fp : 00800000\n r10: 0000071f r9 : 00421000 r8 : 00c00000\n r7 : 00c00000 r6 : 0000071f r5 : ffade000 r4 : 4040171f\n r3 : 00c00000 r2 : 4040171f r1 : c041ac78 r0 : fc6006f0\n Flags: nZcv IRQs off FIQs off Mode SVC_32 ISA ARM Segment none\n Control: 30c5387d Table: 40203000 DAC: 00000001\n Process swapper (pid: 0, stack limit = 0x(ptrval))\n\nSo let\u0027s limit CONFIG_NR_CPUS to 16 when CONFIG_DEBUG_KMAP_LOCAL=y. Also,\nfix the BUILD_BUG_ON() check that was supposed to catch this, by checking\nwhether the region grows below the start address rather than above the end\naddress.",
"id": "GHSA-gg7f-9mpf-7m5f",
"modified": "2024-04-17T18:31:31Z",
"published": "2024-02-27T09:31:15Z",
"references": [
{
"type": "ADVISORY",
"url": "https://nvd.nist.gov/vuln/detail/CVE-2021-46910"
},
{
"type": "WEB",
"url": "https://git.kernel.org/stable/c/5965ac11b1d5fcb38464728931649cd9df79c7c9"
},
{
"type": "WEB",
"url": "https://git.kernel.org/stable/c/d624833f5984d484c5e3196f34b926f9e71dafee"
}
],
"schema_version": "1.4.0",
"severity": [
{
"score": "CVSS:3.1/AV:L/AC:L/PR:L/UI:N/S:U/C:N/I:N/A:H",
"type": "CVSS_V3"
}
]
}
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