CVE-2023-53642

/// Technical description

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

x86: fix clear_user_rep_good() exception handling annotation

This code no longer exists in mainline, because it was removed in

commit d2c95f9d6802 ("x86: don't use REP_GOOD or ERMS for user memory

clearing") upstream.

However, rather than backport the full range of x86 memory clearing and

copying cleanups, fix the exception table annotation placement for the

final 'rep movsb' in clear_user_rep_good(): rather than pointing at the

actual instruction that did the user space access, it pointed to the

register move just before it.

That made sense from a code flow standpoint, but not from an actual

usage standpoint: it means that if user access takes an exception, the

exception handler won't actually find the instruction in the exception

tables.

As a result, rather than fixing it up and returning -EFAULT, it would

then turn it into a kernel oops report instead, something like:

BUG: unable to handle page fault for a

/// 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