CVE-2023-53630 in Linux
Summary
by MITRE • 10/07/2025
In the Linux kernel, the following vulnerability has been resolved:
iommufd: Fix unpinning of pages when an access is present
syzkaller found that the calculation of batch_last_index should use 'start_index' since at input to this function the batch is either empty or it has already been adjusted to cross any accesses so it will start at the point we are unmapping from.
Getting this wrong causes the unmap to run over the end of the pages which corrupts pages that were never mapped. In most cases this triggers the num pinned debugging:
WARNING: CPU: 0 PID: 557 at drivers/iommu/iommufd/pages.c:294 __iopt_area_unfill_domain+0x152/0x560 Modules linked in: CPU: 0 PID: 557 Comm: repro Not tainted 6.3.0-rc2-eeac8ede1755 #1 Hardware name: QEMU Standard PC (i440FX + PIIX, 1996), BIOS rel-1.16.0-0-gd239552ce722-prebuilt.qemu.org 04/01/2014 RIP: 0010:__iopt_area_unfill_domain+0x152/0x560 Code: d2 0f ff 44 8b 64 24 54 48 8b 44 24 48 31 ff 44 89 e6 48 89 44 24 38 e8 fc d3 0f ff 45 85 e4 0f 85 eb 01 00 00 e8 0e d2 0f ff <0f> 0b e8 07 d2 0f ff 48 8b 44 24 38 89 5c 24 58 89 18 8b 44 24 54 RSP: 0018:ffffc9000108baf0 EFLAGS: 00010246 RAX: 0000000000000000 RBX: 00000000ffffffff RCX: ffffffff821e3f85 RDX: 0000000000000000 RSI: ffff88800faf0000 RDI: 0000000000000002 RBP: ffffc9000108bd18 R08: 000000000003ca25 R09: 0000000000000014 R10: 000000000003ca00 R11: 0000000000000024 R12: 0000000000000004 R13: 0000000000000801 R14: 00000000000007ff R15: 0000000000000800 FS: 00007f3499ce1740(0000) GS:ffff88807dc00000(0000) knlGS:0000000000000000 CS: 0010 DS: 0000 ES: 0000 CR0: 0000000080050033 CR2: 0000000020000243 CR3: 00000000179c2001 CR4: 0000000000770ef0 PKRU: 55555554 Call Trace: <TASK> iopt_area_unfill_domain+0x32/0x40 iopt_table_remove_domain+0x23f/0x4c0 iommufd_device_selftest_detach+0x3a/0x90 iommufd_selftest_destroy+0x55/0x70 iommufd_object_destroy_user+0xce/0x130 iommufd_destroy+0xa2/0xc0 iommufd_fops_ioctl+0x206/0x330 __x64_sys_ioctl+0x10e/0x160 do_syscall_64+0x3b/0x90 entry_SYSCALL_64_after_hwframe+0x72/0xdc
Also add some useful WARN_ON sanity checks.
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Analysis
by VulDB Data Team • 04/20/2026
The vulnerability identified as CVE-2023-53630 resides within the Linux kernel's iommufd subsystem, specifically affecting the handling of page unpinning operations when access descriptors are present. This flaw manifests in the incorrect calculation of batch_last_index during the unmap process, which can lead to memory corruption and system instability. The issue was discovered through systematic testing using syzkaller, a powerful fuzzing framework that has proven instrumental in identifying kernel-level vulnerabilities. The root cause stems from a fundamental misunderstanding of the batch state when the function processes unmap operations, where the code incorrectly uses a value that should instead reference start_index.
The technical implementation flaw occurs in the drivers/iommu/iommufd/pages.c file at line 294 within the __iopt_area_unfill_domain function. When the batch is either empty or has already been adjusted to bypass any existing accesses, the code should utilize start_index for calculating batch_last_index. However, the incorrect implementation causes the unmap operation to extend beyond the intended memory boundaries, corrupting pages that were never mapped. This improper boundary calculation creates a memory access violation that triggers the kernel's built-in debugging mechanisms, specifically the num pinned debugging feature that was designed to detect such anomalies. The warning message indicates that the system detected an invalid memory access pattern where the code attempts to operate on memory regions that should not be accessible during the unmap process.
The operational impact of this vulnerability extends beyond simple memory corruption, as it represents a potential pathway for privilege escalation and system instability. When the kernel's memory management subsystem encounters this condition, it generates a critical warning that can indicate a more serious underlying issue in the IOMMU (Input-Output Memory Management Unit) functionality. The system's response to this condition can range from triggering kernel oops messages to potentially causing system crashes or unexpected behavior in virtualized environments where IOMMU functionality is critical. This vulnerability is particularly concerning in containerized environments or virtual machine deployments where IOMMU is used for device assignment and memory isolation. The issue directly relates to CWE-129, which describes improper validation of array indices, and could be classified under ATT&CK technique T1068, as it involves privilege escalation through kernel vulnerabilities.
Mitigation strategies for CVE-2023-53630 should prioritize applying the official kernel patches that correct the batch_last_index calculation logic. System administrators should ensure all affected kernel versions are updated to include the fix that properly handles the start_index value during unmap operations. Additionally, monitoring for kernel warning messages related to num pinned debugging should be implemented as an early detection mechanism, particularly in production environments where IOMMU functionality is actively used. Organizations should also consider implementing runtime protections such as kernel lockdown modes and ensuring that IOMMU is properly configured and enabled for all virtualized workloads. The fix addresses the core issue by ensuring that the batch_last_index calculation uses the appropriate start_index value, thereby preventing the overrunning of memory boundaries and maintaining the integrity of the kernel's memory management subsystem. Regular security audits of kernel components and proactive vulnerability scanning should be maintained to identify similar issues before they can be exploited in operational environments.