CVE-2023-52504

/// Technical 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 ]

/// Remediation

Check the references section for vendor advisories, patches, and mitigation guidance. If immediate patching is not possible, review the CVSS vector to understand the attack surface and apply compensating controls such as network segmentation or access restrictions.

/// References