CVE-2022-48762 in Linux
Summary
by MITRE • 06/20/2024
In the Linux kernel, the following vulnerability has been resolved:
arm64: extable: fix load_unaligned_zeropad() reg indices
In ex_handler_load_unaligned_zeropad() we erroneously extract the data and addr register indices from ex->type rather than ex->data. As ex->type will contain EX_TYPE_LOAD_UNALIGNED_ZEROPAD (i.e. 4): * We'll always treat X0 as the address register, since EX_DATA_REG_ADDR is extracted from bits [9:5]. Thus, we may attempt to dereference an
arbitrary address as X0 may hold an arbitrary value. * We'll always treat X4 as the data register, since EX_DATA_REG_DATA is extracted from bits [4:0]. Thus we will corrupt X4 and cause arbitrary
behaviour within load_unaligned_zeropad() and its caller.
Fix this by extracting both values from ex->data as originally intended.
On an MTE-enabled QEMU image we are hitting the following crash: Unable to handle kernel NULL pointer dereference at virtual address 0000000000000000 Call trace: fixup_exception+0xc4/0x108 __do_kernel_fault+0x3c/0x268 do_tag_check_fault+0x3c/0x104 do_mem_abort+0x44/0xf4 el1_abort+0x40/0x64 el1h_64_sync_handler+0x60/0xa0 el1h_64_sync+0x7c/0x80 link_path_walk+0x150/0x344 path_openat+0xa0/0x7dc do_filp_open+0xb8/0x168 do_sys_openat2+0x88/0x17c __arm64_sys_openat+0x74/0xa0 invoke_syscall+0x48/0x148 el0_svc_common+0xb8/0xf8 do_el0_svc+0x28/0x88 el0_svc+0x24/0x84 el0t_64_sync_handler+0x88/0xec el0t_64_sync+0x1b4/0x1b8 Code: f8695a69 71007d1f 540000e0 927df12a (f940014a)
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Analysis
by VulDB Data Team • 10/30/2024
The vulnerability described in CVE-2022-48762 resides within the Linux kernel's ARM64 architecture implementation, specifically in the exception handling mechanism. This flaw affects the ex_handler_load_unaligned_zeropad() function which is responsible for handling load operations that require unaligned data padding. The issue stems from an incorrect interpretation of register indices during exception handling, creating a potential path for arbitrary code execution and system instability. The vulnerability manifests when the kernel attempts to process load operations on unaligned data, particularly in memory tagging environments where MTE (Memory Tagging Extension) is enabled.
The technical root cause involves improper bit field extraction from the exception table entry structure. The function erroneously extracts both the data register and address register indices from the ex->type field instead of the ex->data field as originally intended. Since ex->type contains the value 4 representing EX_TYPE_LOAD_UNALIGNED_ZEROPAD, this causes the system to always treat X0 as the address register regardless of actual register usage. This misinterpretation leads to attempts at dereferencing arbitrary memory addresses stored in X0, potentially causing null pointer dereferences and kernel crashes. Additionally, the function always treats X4 as the data register due to incorrect bit extraction, resulting in corruption of X4 register contents and unpredictable behavior in the load_unaligned_zeropad() function and its callers.
The operational impact of this vulnerability is severe, particularly in systems utilizing ARM64 architectures with Memory Tagging Extension enabled. The crash scenario described shows a kernel NULL pointer dereference occurring at virtual address zero, indicating that the system attempts to access invalid memory locations due to the corrupted register values. The call trace demonstrates the execution path leading to the fault, starting from fixup_exception through various kernel memory management functions including do_tag_check_fault and do_mem_abort. This vulnerability can be exploited to cause system instability, potentially leading to denial of service conditions or more serious security implications depending on the execution context. The flaw affects the kernel's ability to properly handle unaligned memory load operations, creating a potential attack vector for privilege escalation or system compromise.
Mitigation strategies for this vulnerability require immediate kernel updates to apply the fix that correctly extracts register indices from ex->data rather than ex->type. System administrators should prioritize patching affected ARM64 systems, particularly those running with MTE enabled, as the vulnerability's exploitation risk increases in memory tagging environments. The fix aligns with best practices for exception handling in kernel space, ensuring proper register state management during fault recovery operations. Organizations should also implement monitoring for unusual system behavior or crashes related to memory management functions, as these could indicate exploitation attempts. This vulnerability highlights the importance of careful bit field handling in kernel code and demonstrates how seemingly minor errors in register index extraction can lead to significant security and stability issues. The fix addresses the core issue by ensuring proper alignment with the original design intent, preventing arbitrary memory access patterns and maintaining kernel stability during exception handling operations.
This vulnerability maps to CWE-125 Out-of-bounds Read and CWE-787 Out-of-bounds Write in the Common Weakness Enumeration catalog, reflecting the potential for both unauthorized memory access and data corruption. From an ATT&CK perspective, this flaw could enable techniques such as privilege escalation through kernel exploitation or denial of service via system crash conditions. The vulnerability's exploitation requires specific conditions including MTE-enabled environments and unaligned memory load operations, making it less common but still significant for affected systems. The fix represents a standard defensive programming approach that ensures proper data structure interpretation and maintains the integrity of kernel exception handling mechanisms.