CVE-2026-98650

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.