CVE-2022-49888 in Linux
Summary
by MITRE • 05/01/2025
In the Linux kernel, the following vulnerability has been resolved:
arm64: entry: avoid kprobe recursion
The cortex_a76_erratum_1463225_debug_handler() function is called when handling debug exceptions (and synchronous exceptions from BRK instructions), and so is called when a probed function executes. If the compiler does not inline cortex_a76_erratum_1463225_debug_handler(), it can be probed.
If cortex_a76_erratum_1463225_debug_handler() is probed, any debug exception or software breakpoint exception will result in recursive exceptions leading to a stack overflow. This can be triggered with the ftrace multiple_probes selftest, and as per the example splat below.
This is a regression caused by commit:
6459b8469753e9fe ("arm64: entry: consolidate Cortex-A76 erratum 1463225 workaround")
... which removed the NOKPROBE_SYMBOL() annotation associated with the function.
My intent was that cortex_a76_erratum_1463225_debug_handler() would be inlined into its caller, el1_dbg(), which is marked noinstr and cannot be probed. Mark cortex_a76_erratum_1463225_debug_handler() as __always_inline to ensure this.
Example splat prior to this patch (with recursive entries elided):
| # echo p cortex_a76_erratum_1463225_debug_handler > /sys/kernel/debug/tracing/kprobe_events | # echo p do_el0_svc >> /sys/kernel/debug/tracing/kprobe_events | # echo 1 > /sys/kernel/debug/tracing/events/kprobes/enable | Insufficient stack space to handle exception! | ESR: 0x0000000096000047 -- DABT (current EL) | FAR: 0xffff800009cefff0 | Task stack: [0xffff800009cf0000..0xffff800009cf4000]
| IRQ stack: [0xffff800008000000..0xffff800008004000]
| Overflow stack: [0xffff00007fbc00f0..0xffff00007fbc10f0]
| CPU: 0 PID: 145 Comm: sh Not tainted 6.0.0 #2 | Hardware name: linux,dummy-virt (DT) | pstate: 604003c5 (nZCv DAIF +PAN -UAO -TCO -DIT -SSBS BTYPE=--) | pc : arm64_enter_el1_dbg+0x4/0x20 | lr : el1_dbg+0x24/0x5c | sp : ffff800009cf0000 | x29: ffff800009cf0000 x28: ffff000002c74740 x27: 0000000000000000 | x26: 0000000000000000 x25: 0000000000000000 x24: 0000000000000000 | x23: 00000000604003c5 x22: ffff80000801745c x21: 0000aaaac95ac068 | x20: 00000000f2000004 x19: ffff800009cf0040 x18: 0000000000000000 | x17: 0000000000000000 x16: 0000000000000000 x15: 0000000000000000 | x14: 0000000000000000 x13: 0000000000000000 x12: 0000000000000000 | x11: 0000000000000010 x10: ffff800008c87190 x9 : ffff800008ca00d0 | x8 : 000000000000003c x7 : 0000000000000000 x6 : 0000000000000000 | x5 : 0000000000000000 x4 : 0000000000000000 x3 : 00000000000043a4 | x2 : 00000000f2000004 x1 : 00000000f2000004 x0 : ffff800009cf0040 | Kernel panic - not syncing: kernel stack overflow | CPU: 0 PID: 145 Comm: sh Not tainted 6.0.0 #2 | Hardware name: linux,dummy-virt (DT) | Call trace: | dump_backtrace+0xe4/0x104 | show_stack+0x18/0x4c | dump_stack_lvl+0x64/0x7c | dump_stack+0x18/0x38 | panic+0x14c/0x338 | test_taint+0x0/0x2c | panic_bad_stack+0x104/0x118 | handle_bad_stack+0x34/0x48 | __bad_stack+0x78/0x7c | arm64_enter_el1_dbg+0x4/0x20 | el1h_64_sync_handler+0x40/0x98 | el1h_64_sync+0x64/0x68 | cortex_a76_erratum_1463225_debug_handler+0x0/0x34 ... | el1h_64_sync_handler+0x40/0x98 | el1h_64_sync+0x64/0x68 | cortex_a76_erratum_1463225_debug_handler+0x0/0x34 ... | el1h_64_sync_handler+0x40/0x98 | el1h_64_sync+0x64/0x68 | cortex_a76_erratum_1463225_debug_handler+0x0/0x34 | el1h_64_sync_handler+0x40/0x98 | el1h_64_sync+0x64/0x68 | do_el0_svc+0x0/0x28 | el0t_64_sync_handler+0x84/0xf0 | el0t_64_sync+0x18c/0x190 | Kernel Offset: disabled | CPU features: 0x0080,00005021,19001080 | Memory Limit: none | ---[ end Kernel panic - not syncing: kernel stack overflow ]---
With this patch, cortex_a76_erratum_1463225_debug_handler() is inlined into el1_dbg(), and el1_dbg() cannot be probed:
| # echo p cortex_a76_erratum_1463225_debug_handler > /sys/kernel/debug/tracing/kprobe_events | sh: write error: No such file or directory | # grep -w cortex_a76_errat ---truncated---
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Analysis
by VulDB Data Team • 08/18/2025
The vulnerability CVE-2022-49888 affects the Linux kernel on arm64 architectures and stems from a regression in the handling of debug exceptions related to the Cortex-A76 erratum 1463225 workaround. The issue arises when the function cortex_a76_erratum_1463225_debug_handler() is not inlined, allowing it to be probed by the kernel's kprobes mechanism. This creates a recursive exception scenario where debug exceptions or software breakpoints trigger repeated calls to the same handler, leading to a stack overflow and ultimately a kernel panic. The root cause is traced to commit 6459b8469753e9fe which removed the NOKPROBE_SYMBOL() annotation from the function, breaking the intended inlining behavior.
The technical flaw manifests in the kernel's exception handling pathway where the debug exception handler cortex_a76_erratum_1463225_debug_handler() becomes recursively invoked when kprobes attempt to monitor its execution. This recursive behavior occurs because the function was no longer guaranteed to be inlined into its caller el1_dbg(), which is marked with the noinstr attribute that prevents probing. The system's inability to properly manage stack space during this recursive loop results in a kernel stack overflow, as evidenced by the stack trace showing repeated calls to el1h_64_sync_handler and cortex_a76_erratum_1463225_debug_handler. This vulnerability directly maps to CWE-772, which addresses missing release of resource after effective lifetime, and specifically relates to improper handling of kernel stack resources during exception processing.
The operational impact of this vulnerability is severe as it can lead to complete system crashes and denial of service conditions. An attacker with the ability to manipulate kprobe events or trigger debug exceptions can exploit this weakness to cause kernel panics, making the system unstable and unresponsive. The vulnerability affects systems running kernel versions where the problematic commit was introduced, particularly those utilizing arm64 architectures with Cortex-A76 processors. The exploitation is demonstrated through the ftrace multiple_probes selftest, which shows how simple kprobe setup can trigger the recursive exception chain leading to stack overflow.
The mitigation strategy involves ensuring that cortex_a76_erratum_1463225_debug_handler() is always inlined into its caller el1_dbg() by marking it with __always_inline attribute. This approach prevents the function from being probed and eliminates the recursive exception path by ensuring it cannot be independently monitored by kprobes. The fix aligns with ATT&CK technique T1059.006, which involves the use of kernel modules or kernel exploits to manipulate system behavior, by preventing the conditions that enable such manipulation. Additionally, this vulnerability highlights the importance of proper symbol annotation and inlining strategies in kernel code, particularly for functions that are part of critical exception handling paths. The resolution ensures that the function remains inlined and protected from external probing while maintaining the intended erratum workaround functionality.