CVE-2024-36926 in Linux
Summary
by MITRE • 05/30/2024
In the Linux kernel, the following vulnerability has been resolved:
powerpc/pseries/iommu: LPAR panics during boot up with a frozen PE
At the time of LPAR boot up, partition firmware provides Open Firmware property ibm,dma-window for the PE. This property is provided on the PCI bus the PE is attached to.
There are execptions where the partition firmware might not provide this property for the PE at the time of LPAR boot up. One of the scenario is where the firmware has frozen the PE due to some error condition. This PE is frozen for 24 hours or unless the whole system is reinitialized.
Within this time frame, if the LPAR is booted, the frozen PE will be presented to the LPAR but ibm,dma-window property could be missing.
Today, under these circumstances, the LPAR oopses with NULL pointer dereference, when configuring the PCI bus the PE is attached to.
BUG: Kernel NULL pointer dereference on read at 0x000000c8 Faulting instruction address: 0xc0000000001024c0 Oops: Kernel access of bad area, sig: 7 [#1]
LE PAGE_SIZE=64K MMU=Radix SMP NR_CPUS=2048 NUMA pSeries Modules linked in: Supported: Yes CPU: 0 PID: 1 Comm: swapper/0 Not tainted 6.4.0-150600.9-default #1 Hardware name: IBM,9043-MRX POWER10 (raw) 0x800200 0xf000006 of:IBM,FW1060.00 (NM1060_023) hv:phyp pSeries NIP: c0000000001024c0 LR: c0000000001024b0 CTR: c000000000102450 REGS: c0000000037db5c0 TRAP: 0300 Not tainted (6.4.0-150600.9-default) MSR: 8000000002009033 CR: 28000822 XER: 00000000 CFAR: c00000000010254c DAR: 00000000000000c8 DSISR: 00080000 IRQMASK: 0 ... NIP [c0000000001024c0] pci_dma_bus_setup_pSeriesLP+0x70/0x2a0
LR [c0000000001024b0] pci_dma_bus_setup_pSeriesLP+0x60/0x2a0
Call Trace: pci_dma_bus_setup_pSeriesLP+0x60/0x2a0 (unreliable) pcibios_setup_bus_self+0x1c0/0x370 __of_scan_bus+0x2f8/0x330 pcibios_scan_phb+0x280/0x3d0 pcibios_init+0x88/0x12c do_one_initcall+0x60/0x320 kernel_init_freeable+0x344/0x3e4 kernel_init+0x34/0x1d0 ret_from_kernel_user_thread+0x14/0x1c
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Analysis
by VulDB Data Team • 05/30/2024
This vulnerability affects the Linux kernel's handling of IOMMU configuration during PowerPC LPAR (Logical Partition) boot processes. The issue specifically occurs when partition firmware provides an Open Firmware property called ibm,dma-window for a PCI bus that is attached to a PE (Partition Entity). This property is crucial for DMA window configuration and memory mapping operations within the IOMMU subsystem. When the firmware has frozen a PE due to error conditions, it may not provide this required property during LPAR boot up, creating a scenario where the system cannot properly initialize the DMA mapping infrastructure.
The technical flaw manifests as a NULL pointer dereference during kernel execution in the pci_dma_bus_setup_pSeriesLP function at offset 0x70 in the code sequence. The fault occurs at memory address 0x000000c8 which corresponds to a critical data structure access within the IOMMU setup code. This dereference happens because the code attempts to access a DMA window structure that was not properly initialized due to the missing ibm,dma-window property. The kernel's architecture-specific powerpc/pseries/iommu subsystem fails to handle the exceptional case where firmware provides insufficient information, leading to an immediate system crash rather than graceful error handling.
The operational impact of this vulnerability is severe as it causes complete system panics during LPAR boot processes, preventing normal operation of virtualized systems. The frozen PE condition can persist for up to 24 hours or until complete system reinitialization, meaning that affected systems may become unusable for extended periods. This affects enterprise systems running on POWER10 processors and other PowerPC-based platforms that utilize LPAR virtualization. The vulnerability represents a critical failure in the kernel's error handling mechanisms, as it should be able to detect missing firmware properties and either defer initialization or provide fallback mechanisms rather than crashing the entire system.
The root cause aligns with CWE-476 which describes NULL pointer dereference conditions in software systems. From an ATT&CK framework perspective, this vulnerability relates to privilege escalation and system compromise through kernel-level exploitation, potentially enabling adversaries to cause denial of service conditions or gain deeper system access. The vulnerability also demonstrates weaknesses in firmware-to-kernel communication protocols and the absence of proper fallback mechanisms for critical system components. Effective mitigations should include enhanced error handling in the kernel's IOMMU initialization code, proper validation of firmware-provided properties, and implementation of graceful degradation strategies when essential configuration data is missing. Additionally, system administrators should ensure firmware updates are applied to address known issues with PE freezing conditions and DMA window property generation.