CVE-2024-42293

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

arm64: mm: Fix lockless walks with static and dynamic page-table folding

Lina reports random oopsen originating from the fast GUP code when 16K pages are used with 4-level page-tables, the fourth level being folded at runtime due to lack of LPA2.

In this configuration, the generic implementation of p4d_offset_lockless() will return a p4d_t * corresponding to the pgd_t allocated on the stack of the caller, gup_fast_pgd_range(). This is normally fine, but when the fourth level of page-table is folded at runtime, pud_offset_lockless() will offset from the address of the p4d_t to calculate the address of the PUD in the same page-table page. This results in a stray stack read when the p4d_t has been allocated on the stack and can send the walker into the weeds.

Fix the problem by providing our own definition of p4d_offset_lockless() when CONFIG_PGTABLE_LEVELS <= 4 which returns the real page-table pointer rather than the address of the local stack variable.

Affected Software

References

• https://git.kernel.org/stable/c/36639013b3462c06ff8e3400a427f775b4fc97f5
• https://git.kernel.org/stable/c/78672d49d3eebbcda3589f4d6e589caf357c5a59