x86/alternatives: Disable KASAN in apply_alternatives()

Vulnerability Description

In the Linux kernel, the following vulnerability has been resolved: x86/alternatives: Disable KASAN in apply_alternatives() Fei has reported that KASAN triggers during apply_alternatives() on a 5-level paging machine: BUG: KASAN: out-of-bounds in rcu_is_watching() Read of size 4 at addr ff110003ee6419a0 by task swapper/0/0 ... __asan_load4() rcu_is_watching() trace_hardirqs_on() text_poke_early() apply_alternatives() ... On machines with 5-level paging, cpu_feature_enabled(X86_FEATURE_LA57) gets patched. It includes KASAN code, where KASAN_SHADOW_START depends on __VIRTUAL_MASK_SHIFT, which is defined with cpu_feature_enabled(). KASAN gets confused when apply_alternatives() patches the KASAN_SHADOW_START users. A test patch that makes KASAN_SHADOW_START static, by replacing __VIRTUAL_MASK_SHIFT with 56, works around the issue. Fix it for real by disabling KASAN while the kernel is patching alternatives. [ mingo: updated the changelog ]

References

• https://git.kernel.org/stable/c/3719d3c36aa853d5a2401af9f8d6b116c91ad5ae
• https://git.kernel.org/stable/c/3770c38cd6a60494da29ac2da73ff8156440a2d1
• https://git.kernel.org/stable/c/6788b10620ca6e98575d1e06e72a8974aad7657e
• https://git.kernel.org/stable/c/ecba5afe86f30605eb9dfb7f265a8de0218d4cfc
• https://git.kernel.org/stable/c/5b784489c8158518bf7a466bb3cc045b0fb66b4b
• https://git.kernel.org/stable/c/cd287cc208dfe6bd6da98e7f88e723209242c9b4
• https://git.kernel.org/stable/c/d35652a5fc9944784f6f50a5c979518ff8dacf61