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 ]

Classification

CVE ID: CVE-2023-52504

Affected Products

Vendor: Linux

Product: Linux

Exploit Prediction Scoring System (EPSS)

EPSS Score: 0.04% (probability of being exploited)

EPSS Percentile: 5.06% (scored less or equal to compared to others)

EPSS Date: 2025-02-03 (when was this score calculated)

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

Timeline