CVE-2025-40048: uio_hv_generic: Let userspace take care of interrupt mask
In the Linux kernel, the following vulnerability has been resolved:
uiohvgeneric: Let userspace take care of interrupt mask
Remove the logic to set interrupt mask by default in uiohvgeneric driver as the interrupt mask value is supposed to be controlled completely by the user space. If the mask bit gets changed by the driver, concurrently with user mode operating on the ring, the mask bit may be set when it is supposed to be clear, and the user-mode driver will miss an interrupt which will cause a hang.
For eg- when the driver sets inbound ring buffer interrupt mask to 1, the host does not interrupt the guest on the UIO VMBus channel. However, setting the mask does not prevent the host from putting a message in the inbound ring buffer. So let’s assume that happens, the host puts a message into the ring buffer but does not interrupt.
Subsequently, the user space code in the guest sets the inbound ring buffer interrupt mask to 0, saying “Hey, I’m ready for interrupts”. User space code then calls pread() to wait for an interrupt. Then one of two things happens:
The host never sends another message. So the pread() waits forever. The host does send another message. But because there’s already a message in the ring buffer, it doesn’t generate an interrupt. This is the correct behavior, because the host should only send an interrupt when the inbound ring buffer transitions from empty to not-empty. Adding an additional message to a ring buffer that is not empty is not supposed to generate an interrupt on the guest. Since the guest is waiting in pread() and not removing messages from the ring buffer, the pread() waits forever.
This could be easily reproduced in hvfcopyuiodaemon if we delay setting interrupt mask to 0.
Similarly if hvuiochannelcb() sets the interruptmask to 1, there’s a race condition. Once user space empties the inbound ring buffer, but before user space sets interruptmask to 0, the host could put another message in the ring buffer but it wouldn’t interrupt. Then the next pread() would hang.
Fix these by removing all instances where interruptmask is changed, while keeping the one in setevent() unchanged to enable userspace control the interrupt mask by writing 0/1 to /dev/uioX.
Affected Software
Remediation
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Remove the driver's default and callback logic that changes interrupt_mask, while keeping the interrupt_mask update in set_event() so userspace exclusively controls the mask.
uio_hv_generic interrupt_mask = userspace-controlled via set_event() by writing 0/1 to /dev/uioX
Event History
Frequently Asked Questions
What is the severity of CVE-2025-40048?
CVE-2025-40048 is categorized as a moderate severity vulnerability in the Linux kernel.
How do I fix CVE-2025-40048?
To fix CVE-2025-40048, update your Linux kernel to the latest available version that addresses this vulnerability.
What impact does CVE-2025-40048 have on system security?
CVE-2025-40048 could potentially allow unauthorized users to gain control over interrupt masking, affecting system integrity.
Is my system vulnerable to CVE-2025-40048?
If you are running an affected version of the Linux kernel, you may be vulnerable to CVE-2025-40048.
How can I check my Linux kernel version for CVE-2025-40048?
You can check your Linux kernel version by running the command 'uname -r' in your terminal.