CVE-2025-38010 in Linux
Summary
by MITRE • 06/18/2025
In the Linux kernel, the following vulnerability has been resolved:
phy: tegra: xusb: Use a bitmask for UTMI pad power state tracking
The current implementation uses bias_pad_enable as a reference count to manage the shared bias pad for all UTMI PHYs. However, during system suspension with connected USB devices, multiple power-down requests for the UTMI pad result in a mismatch in the reference count, which in turn produces warnings such as:
[ 237.762967] WARNING: CPU: 10 PID: 1618 at tegra186_utmi_pad_power_down+0x160/0x170
[ 237.763103] Call trace:
[ 237.763104] tegra186_utmi_pad_power_down+0x160/0x170
[ 237.763107] tegra186_utmi_phy_power_off+0x10/0x30
[ 237.763110] phy_power_off+0x48/0x100
[ 237.763113] tegra_xusb_enter_elpg+0x204/0x500
[ 237.763119] tegra_xusb_suspend+0x48/0x140
[ 237.763122] platform_pm_suspend+0x2c/0xb0
[ 237.763125] dpm_run_callback.isra.0+0x20/0xa0
[ 237.763127] __device_suspend+0x118/0x330
[ 237.763129] dpm_suspend+0x10c/0x1f0
[ 237.763130] dpm_suspend_start+0x88/0xb0
[ 237.763132] suspend_devices_and_enter+0x120/0x500
[ 237.763135] pm_suspend+0x1ec/0x270
The root cause was traced back to the dynamic power-down changes introduced in commit a30951d31b25 ("xhci: tegra: USB2 pad power controls"), where the UTMI pad was being powered down without verifying its current state. This unbalanced behavior led to discrepancies in the reference count.
To rectify this issue, this patch replaces the single reference counter with a bitmask, renamed to utmi_pad_enabled. Each bit in the mask corresponds to one of the four USB2 PHYs, allowing us to track each pad's enablement status individually.
With this change: - The bias pad is powered on only when the mask is clear. - Each UTMI pad is powered on or down based on its corresponding bit in the mask, preventing redundant operations. - The overall power state of the shared bias pad is maintained correctly during suspend/resume cycles.
The mutex used to prevent race conditions during UTMI pad enable/disable operations has been moved from the tegra186_utmi_bias_pad_power_on/off functions to the parent functions tegra186_utmi_pad_power_on/down. This change ensures that there are no race conditions when updating the bitmask.
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Analysis
by VulDB Data Team • 02/02/2026
The vulnerability CVE-2025-38010 affects the Linux kernel's Tegra XUSB PHY driver, specifically targeting the management of UTMI pad power states within the Tegra186 SoC architecture. This issue manifests as a reference count mismatch during system suspension when USB devices remain connected, leading to kernel warnings and potential instability in power management operations. The flaw stems from improper handling of shared bias pad resources across multiple USB2 PHYs, creating a scenario where redundant power-down operations can occur without proper state verification.
The technical implementation flaw involves the use of a reference counter variable named bias_pad_enable to track the shared bias pad state for all UTMI PHYs. During system suspension, multiple power-down requests can be issued simultaneously for different USB2 PHYs, causing the reference count to become misaligned with the actual hardware state. This misalignment results in kernel warnings indicating that power-down operations are being performed when the pad is already powered down, as evidenced by the call trace showing tegra186_utmi_pad_power_down being invoked from various suspension-related functions including tegra_xusb_enter_elpg and platform_pm_suspend. The root cause was introduced in a previous commit that implemented dynamic power-down changes without proper state validation before initiating pad power-down operations.
The operational impact of this vulnerability extends beyond mere warning messages to potentially compromise system stability during power management transitions. The reference count mismatch can lead to incorrect power state tracking, where the system believes a pad is in one state while it's actually in another. This creates a race condition scenario where concurrent power management operations can interfere with each other, potentially causing the shared bias pad to be powered on or off at inappropriate times. The vulnerability specifically affects systems using Tegra186 SoC with USB2 PHYs, particularly during suspend/resume cycles when multiple USB devices are connected, making it a significant concern for mobile and embedded systems where power management is critical.
The mitigation implemented in this patch addresses the core issue by replacing the reference counter mechanism with a bitmask approach using a new variable named utmi_pad_enabled. This bitmask approach provides individual tracking for each of the four USB2 PHYs, eliminating the race conditions that occurred with the previous reference counting method. Each bit in the mask corresponds to a specific UTMI pad, allowing the system to determine whether a particular pad should be powered on or off based on its individual state rather than relying on a shared counter. The power management logic is enhanced to power on the bias pad only when all bits in the mask are clear, and to power down individual pads based on their corresponding mask bits, thereby preventing redundant operations. Additionally, the mutex protection has been relocated from the bias pad power functions to the parent pad power functions to ensure proper synchronization during bitmask updates, aligning with best practices for concurrent access control in kernel drivers.
This vulnerability aligns with CWE-691, which covers insufficient control flow management in software systems, particularly in the context of power management and resource allocation. The issue also relates to ATT&CK technique T1547.001, which involves privilege escalation through kernel-level modifications, as improper power management can create conditions that might be exploited to gain elevated privileges. The fix demonstrates proper adherence to kernel security principles by implementing atomic operations and proper synchronization mechanisms, ensuring that shared resources are managed correctly during concurrent access scenarios. The change also reflects the kernel's ongoing efforts to address race conditions and resource management issues that can lead to system instability and potential security vulnerabilities in embedded systems where power management is critical for both performance and security.