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CVE-2021-47640

powerpc/kasan: Fix early region not updated correctly

High7.8EPSS 0.26%
Published
Updated
Reserved
Assigned by
Linux

Description

In the Linux kernel, the following vulnerability has been resolved: powerpc/kasan: Fix early region not updated correctly The shadow's page table is not updated when PTE_RPN_SHIFT is 24 and PAGE_SHIFT is 12. It not only causes false positives but also false negative as shown the following text. Fix it by bringing the logic of kasan_early_shadow_page_entry here. 1. False Positive: ================================================================== BUG: KASAN: vmalloc-out-of-bounds in pcpu_alloc+0x508/0xa50 Write of size 16 at addr f57f3be0 by task swapper/0/1 CPU: 0 PID: 1 Comm: swapper/0 Not tainted 5.15.0-12267-gdebe436e77c7 #1 Call Trace: [c80d1c20] [c07fe7b8] dump_stack_lvl+0x4c/0x6c (unreliable) [c80d1c40] [c02ff668] print_address_description.constprop.0+0x88/0x300 [c80d1c70] [c02ff45c] kasan_report+0x1ec/0x200 [c80d1cb0] [c0300b20] kasan_check_range+0x160/0x2f0 [c80d1cc0] [c03018a4] memset+0x34/0x90 [c80d1ce0] [c0280108] pcpu_alloc+0x508/0xa50 [c80d1d40] [c02fd7bc] __kmem_cache_create+0xfc/0x570 [c80d1d70] [c0283d64] kmem_cache_create_usercopy+0x274/0x3e0 [c80d1db0] [c2036580] init_sd+0xc4/0x1d0 [c80d1de0] [c00044a0] do_one_initcall+0xc0/0x33c [c80d1eb0] [c2001624] kernel_init_freeable+0x2c8/0x384 [c80d1ef0] [c0004b14] kernel_init+0x24/0x170 [c80d1f10] [c001b26c] ret_from_kernel_thread+0x5c/0x64 Memory state around the buggy address: f57f3a80: f8 f8 f8 f8 f8 f8 f8 f8 f8 f8 f8 f8 f8 f8 f8 f8 f57f3b00: f8 f8 f8 f8 f8 f8 f8 f8 f8 f8 f8 f8 f8 f8 f8 f8 >f57f3b80: f8 f8 f8 f8 f8 f8 f8 f8 f8 f8 f8 f8 f8 f8 f8 f8 ^ f57f3c00: f8 f8 f8 f8 f8 f8 f8 f8 f8 f8 f8 f8 f8 f8 f8 f8 f57f3c80: f8 f8 f8 f8 f8 f8 f8 f8 f8 f8 f8 f8 f8 f8 f8 f8 ================================================================== 2. False Negative (with KASAN tests): ================================================================== Before fix: ok 45 - kmalloc_double_kzfree # vmalloc_oob: EXPECTATION FAILED at lib/test_kasan.c:1039 KASAN failure expected in "((volatile char *)area)[3100]", but none occurred not ok 46 - vmalloc_oob not ok 1 - kasan ================================================================== After fix: ok 1 - kasan

Timeline

  1. ID reserved

    By Linux

  2. Published

  3. · 15 months later

    Record updated

Changes after publication (a new score, a public exploit, EPSS crossing 1, 10 or 50 %, leaving KEV) are kept since November 2026; earlier ones are not known.

Scores

CVSS scores of CVE-2021-47640, by who scored it
Scored byCVSSScoreVector
CISA-ADPADP (enrichment)3.1High7.8CVSS:3.1/AV:L/AC:L/PR:L/UI:N/S:U/C:H/I:H/A:H
NVDNVD · Modified3.1High7.8CVSS:3.1/AV:L/AC:L/PR:L/UI:N/S:U/C:H/I:H/A:H
EPSS (exploitation in 30 days)
0.26% · top 82% of all CVEs (7 Nov 2026)
CISA SSVC
Exploitation: none · Automatable: no · Technical impact: total
Loading the EPSS history…

The list uses the assigner's score when there is one, then CISA's, then NVD's: High 7.8.

Weakness

Affected products

  • Linux · Linux

    • affected cbd18991e24fea2c31da3bb117c83e4a3538cd11 – < 7f19245c3647afea8c7c41f795506ef70f64b9f2
    • affected cbd18991e24fea2c31da3bb117c83e4a3538cd11 – < f39a3309393a4a484532f6ba745c6acbcfe06115
    • affected cbd18991e24fea2c31da3bb117c83e4a3538cd11 – < 5a3d8f3192a409893c57808cc935e16484df1068
    • affected cbd18991e24fea2c31da3bb117c83e4a3538cd11 – < de56beace6648065d404cd9835aa7d30e3df519d
    • affected cbd18991e24fea2c31da3bb117c83e4a3538cd11 – < e3d157a4b4f4e0268c98be5b7013bf4b31234bb6
    • affected cbd18991e24fea2c31da3bb117c83e4a3538cd11 – < dd75080aa8409ce10d50fb58981c6b59bf8707d3
    • affected 3822dd8c102d11ada9d9ed8e04cad0b347a04689
    • affected 5.3.6 – < 5.4

  • Linux · Linux

    • affected 5.4
    • unaffected < 5.4
    • unaffected 5.4.189 – ≤ 5.4.*
    • unaffected 5.10.110 – ≤ 5.10.*
    • unaffected 5.15.33 – ≤ 5.15.*
    • unaffected 5.16.19 – ≤ 5.16.*
    • unaffected 5.17.2 – ≤ 5.17.*
    • unaffected 5.18 – ≤ *

References (6)

Sources

The same CVE in the primary databases and aggregators, to check against.

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Record last updated .