CVE-2021-47640

Summary

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

  1. 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

Affected Software

VendorProductVersion RangeStatus
LinuxLinuxcbd18991e24fea2c31da3bb117c83e4a3538cd11 < 7f19245c3647afea8c7c41f795506ef70f64b9f2affected
LinuxLinuxcbd18991e24fea2c31da3bb117c83e4a3538cd11 < f39a3309393a4a484532f6ba745c6acbcfe06115affected
LinuxLinuxcbd18991e24fea2c31da3bb117c83e4a3538cd11 < 5a3d8f3192a409893c57808cc935e16484df1068affected
LinuxLinuxcbd18991e24fea2c31da3bb117c83e4a3538cd11 < de56beace6648065d404cd9835aa7d30e3df519daffected
LinuxLinuxcbd18991e24fea2c31da3bb117c83e4a3538cd11 < e3d157a4b4f4e0268c98be5b7013bf4b31234bb6affected
LinuxLinuxcbd18991e24fea2c31da3bb117c83e4a3538cd11 < dd75080aa8409ce10d50fb58981c6b59bf8707d3affected
LinuxLinux3822dd8c102d11ada9d9ed8e04cad0b347a04689affected
LinuxLinux5.3.6 < 5.4affected
LinuxLinux5.4affected
LinuxLinux0 < 5.4unaffected
LinuxLinux5.4.189 <= 5.4.*unaffected
LinuxLinux5.10.110 <= 5.10.*unaffected
LinuxLinux5.15.33 <= 5.15.*unaffected
LinuxLinux5.16.19 <= 5.16.*unaffected
LinuxLinux5.17.2 <= 5.17.*unaffected
LinuxLinux5.18 <= *unaffected

Weaknesses

ADP Enrichment

CISA ADP Vulnrichment

  • SSVC:
  • Exploitation: none
    • Automatable: no
    • Technical Impact: total

References