CVE-2022-49888 in Linux
Riassunto
di VulDB • 29/06/2026
Based on the log and description provided, here is an analysis of the issue and a solution.
### Problem Analysis
1. **Kernel Panic Cause**: The system crashed with `kernel stack overflow`. This typically happens when a function consumes too much stack space or recurses infinitely without returning. In this specific trace, it appears to be triggered during exception handling (`el1h_64_sync_handler`). 2. **The Erratum Handler**: The call trace shows repeated calls to: ```c cortex_a76_erratum_1463225_debug_handler+0x0/0x34 el1h_64_sync_handler+0x40/0x98 el1h_64_sync+0x64/0x68 ``` This pattern suggests an infinite loop or deep recursion involving the Cortex-A76 erratum 1463225 debug handler. Erratum 1463225 relates to incorrect behavior of the Debug Exception Mask Register (DBGMCR_EL1) when using AArch64 Debug Architecture v8.0+. The kernel includes a workaround (`cortex_a76_erratum_1463225_debug_handler`) to handle this hardware bug during debug operations. 3. **Kprobe Failure**: You attempted to set up a kprobe on `cortex_a76_erratum_1463225_debug_handler` using: ```bash echo p cortex_a76_erratum_1463225_debug_handler > /sys/kernel/debug/tracing/kprobe_events ``` This failed with "No such file or directory" (which in this context usually means the symbol is not found as a probeable target). The explanation given is that **the function has been inlined into `el1_dbg()`**.
### Why Inlining Prevents Kprobing
* **Inlining**: When a compiler inlines a small function, it replaces the call site with the actual code of the function. There is no longer a distinct symbol or entry point for `cortex_a76_erratum_1463225_debug_handler` at runtime; its instructions are merged into `el1_dbg()`. * **Kprobes Requirement**: Kprobes work by inserting an instruction (like `int 3` on x86 or a breakpoint trap) at the beginning of a function's symbol. If the symbol doesn't exist as a separate entity in the kernel image, kprobe cannot attach to it.
### Solutions and Workarounds
#### Option 1: Probe the Parent Function (`el1_dbg`) Since `cortex_a76_erratum_1463225_debug_handler` is now part of `el1_dbg`, you should probe `el1_dbg` instead. However, note that `el1_dbg` might be called frequently or in sensitive contexts (debug exceptions), so probing it may have performance implications or cause instability if not handled carefully.
```bash # Try to probe the parent function echo p el1_dbg > /sys/kernel/debug/tracing/kprobe_events ```
If this succeeds, you can analyze events related to debug entry points. To distinguish calls that involve the erratum handler, you may need to look at instruction offsets within `el1_dbg` if possible (though kprobes on inlined functions don't easily allow offset-based probing for specific inline blocks).
#### Option 2: Disable Inlining via Compiler Flag If you are building a custom kernel and want this function to be probeable, you can prevent the compiler from inlining it. Add `__attribute__((noinline))` to its definition or use `-fno-inline-functions-called-once` if appropriate for your build system.
In the Linux kernel source (typically under `arch/arm64/kernel/debug-monitors.c`), find: ```c static void cortex_a76_erratum_1463225_debug_handler(void) {
... } ``` Change it to: ```c __attribute__((noinline)) static void cortex_a76_erratum_1463225_debug_handler(void) {
... } ```
#### Option 3: Use ftrace or eBPF Instead of Kprobes If kprobe is not feasible due to inlining, consider using **ftrace** function tracer or **eBPF**: * **Ftrace**: Trace `el1_dbg` and filter for relevant conditions. ```bash echo el1_dbg > /sys/kernel/debug/tracing/set_ftrace_filter cat /proc/sys/kernel/ftrace_enabled # Ensure it's enabled ``` * **eBPF**: Write an eBPF
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