CVE-2021-47567: 
Linux Debian vulnerability analysis and mitigation

CVE-2021-47567 affects the Linux kernel's PowerPC 32-bit architecture implementation. The vulnerability was discovered when a vmap stack overflow condition resulted in a hard lockup due to incorrect address handling after a previous fix (commit c118c7303ad5). The issue was introduced when the MMU handling was modified for task struct reading, causing emergency_ctx to be incorrectly addressed with its virtual address when the data MMU was inactive (Kernel Git).

The vulnerability stems from improper handling of virtual addresses in the PowerPC 32-bit architecture's emergency context during vmap stack overflow conditions. Specifically, when the data MMU is not active, the system still attempts to use virtual addressing for emergency_ctx instead of physical addressing. The fix involves modifying the address calculation in arch/powerpc/kernel/head_32.h to use physical addresses by subtracting PAGE_OFFSET from the emergency_ctx address (Kernel Git).

When exploited, this vulnerability results in a hard lockup of the system when a vmap stack overflow occurs on PowerPC 32-bit architectures. This effectively causes a denial of service condition as the system becomes unresponsive (Kernel Git).

The vulnerability is triggered by a vmap stack overflow condition in PowerPC 32-bit systems running affected Linux kernel versions. The issue occurs in a critical system context, specifically during emergency context handling (Kernel Git).

The vulnerability has been fixed by modifying the address calculation to use physical addresses instead of virtual addresses for emergency_ctx when the MMU is inactive. The fix was implemented in the Linux kernel and is available through kernel updates. Users should update to a patched kernel version that includes the fix (Kernel Git).