CVE-2024-56678

/// Technical description

In the Linux kernel, the following vulnerability has been resolved:

powerpc/mm/fault: Fix kfence page fault reporting

copy_from_kernel_nofault() can be called when doing read of /proc/kcore.

/proc/kcore can have some unmapped kfence objects which when read via

copy_from_kernel_nofault() can cause page faults. Since *_nofault()

functions define their own fixup table for handling fault, use that

instead of asking kfence to handle such faults.

Hence we search the exception tables for the nip which generated the

fault. If there is an entry then we let the fixup table handler handle the

page fault by returning an error from within ___do_page_fault().

This can be easily triggered if someone tries to do dd from /proc/kcore.

eg. dd if=/proc/kcore of=/dev/null bs=1M

Some example false negatives:

===============================

BUG: KFENCE: invalid read in copy_from_kernel_nofault+0x9c/0x1a0

Invalid read at 0xc0000000fdff0000:

copy_from_kernel_nofault+0x9c/0x1a0

0xc00000000665f

/// 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