CVE-2026-98650KVM: s390: Fix potential races in dat skey functions

Official description

In the Linux kernel, the following vulnerability has been resolved: KVM: s390: Fix potential races in dat skey functions When dat_cond_set_storage_key() finds a large page, it will conditionally set the storage key in absolute memory using large_crste_to_phys() to get the absolute address. There is a race window between dat_entry_walk() and large_crste_to_phys(): the large page could have been split concurrently, and large_crste_to_phys() might be called with a crste that does not designate a large page, leading to crashes. Similar issues were also present in dat_set_storage_key(). dat_get_storage_key() and dat_reset_reference_bit() did instead check for a potential concurrent splitting of the large page, but then handled it incorrectly. Fix by performing a READ_ONCE on the crste pointer, checking and using the result, instead of dereferencing the pointer again. In case a race is detacted, try dat_entry_walk() again.

Affected packages & fixed versions

Affected products (as reported)

References

• https://git.kernel.org/stable/c/c958f0498891203fddf2764b28f8b102c6bfd719
• https://git.kernel.org/stable/c/27554b9505ddfc0aeab466aeb60929dfa17284c7