In the Linux kernel, the following vulnerability has been resolved: x86/alternatives: Disable KASAN in applyalternatives() Fei has reported that KASAN triggers during applyalternatives() on a 5-level paging machine: BUG: KASAN: out-of-bounds in rcuiswatching() Read of size 4 at addr ff110003ee6419a0 by task swapper/0/0 ... _asanload4() rcuiswatching() tracehardirqson() textpokeearly() applyalternatives() ... On machines with 5-level paging, cpufeatureenabled(X86FEATURELA57) gets patched. It includes KASAN code, where KASANSHADOWSTART depends on _VIRTUALMASKSHIFT, which is defined with cpufeatureenabled(). KASAN gets confused when applyalternatives() patches the KASANSHADOWSTART users. A test patch that makes KASANSHADOWSTART static, by replacing _VIRTUALMASKSHIFT with 56, works around the issue. Fix it for real by disabling KASAN while the kernel is patching alternatives. [ mingo: updated the changelog ]