CVE-2024-44965: Undefined Security Weakness

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

x86/mm: Fix pti_clone_pgtable() alignment assumption

Guenter reported dodgy crashes on an i386-nosmp build using GCC-11 that had the form of endless traps until entry stack exhaust and then #DF from the stack guard.

It turned out that pti_clone_pgtable() had alignment assumptions on the start address, notably it hard assumes start is PMD aligned. This is true on x86_64, but very much not true on i386.

These assumptions can cause the end condition to malfunction, leading to a 'short' clone. Guess what happens when the user mapping has a short copy of the entry text?

Use the correct increment form for addr to avoid alignment assumptions.