Executive brief
A technical issue in the Linux kernel for ARM-based systems can cause the operating system to crash during startup. This occurs when specific memory safety features are enabled on older ARMv5 hardware. While this primarily affects system stability and availability, it prevents the system from booting successfully.
Technical details
The vulnerability stems from an unaligned word load (ldr) in the __switch_to() function on ARMv5 architectures. A previous commit added a dummy read from the KASAN VMAP stack shadow, but because KASAN shadow addresses are byte-granular, they are not guaranteed to be word-aligned. ARMv5 hardware triggers an alignment exception (fault) when encountering unaligned word loads, leading to a kernel panic/crash before reaching the init process. The fix replaces the word load (ldr) with a byte load (ldrb), which is sufficient for faulting in the shadow mapping and avoids alignment requirements. This affects systems configured with CONFIG_KASAN_VMALLOC and CONFIG_VMAP_STACK.
Affected products
- Linux Linux Kernel v6.13+
Timeline
- 2026-05-24: disclosed: Initial patch authored
- 2026-06-19: patched: Patch committed to stable branches
- 2026-07-01: advisory: CVE published
References
- https://git.kernel.org/stable/c/2a4dc9a0ac3326e79fb58fdaae724b92127709a9
- https://git.kernel.org/stable/c/517720913bd3c17a52cd55a740064f68455ab88e
- https://git.kernel.org/stable/c/77a1f6883dc6e837bb2cb30b9b02e2f94338e2c6
- https://git.kernel.org/stable/c/c0b8c148a7754826156993ed6442d31536ec86b4
- https://git.kernel.org/stable/c/c2e3aadc8fef7da068490597fc5582f8f362aeb2
- https://git.kernel.org/stable/c/c74990828d3c486ee44aaa68240eb3abff289d1c