CVE-2021-47640

/// Technical 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_cach

/// Remediation

Check the references section for vendor advisories, patches, and mitigation guidance. If immediate patching is not possible, review the CVSS vector to understand the attack surface and apply compensating controls such as network segmentation or access restrictions.

/// References