CVE-2024-49993
iommu/vt-d: Fix potential lockup if qi_submit_sync called with 0 count
Severity Score
Exploit Likelihood
Affected Versions
Public Exploits
0Exploited in Wild
-Decision
Descriptions
In the Linux kernel, the following vulnerability has been resolved:
iommu/vt-d: Fix potential lockup if qi_submit_sync called with 0 count
If qi_submit_sync() is invoked with 0 invalidation descriptors (for
instance, for DMA draining purposes), we can run into a bug where a
submitting thread fails to detect the completion of invalidation_wait.
Subsequently, this led to a soft lockup. Currently, there is no impact
by this bug on the existing users because no callers are submitting
invalidations with 0 descriptors. This fix will enable future users
(such as DMA drain) calling qi_submit_sync() with 0 count.
Suppose thread T1 invokes qi_submit_sync() with non-zero descriptors, while
concurrently, thread T2 calls qi_submit_sync() with zero descriptors. Both
threads then enter a while loop, waiting for their respective descriptors
to complete. T1 detects its completion (i.e., T1's invalidation_wait status
changes to QI_DONE by HW) and proceeds to call reclaim_free_desc() to
reclaim all descriptors, potentially including adjacent ones of other
threads that are also marked as QI_DONE.
During this time, while T2 is waiting to acquire the qi->q_lock, the IOMMU
hardware may complete the invalidation for T2, setting its status to
QI_DONE. However, if T1's execution of reclaim_free_desc() frees T2's
invalidation_wait descriptor and changes its status to QI_FREE, T2 will
not observe the QI_DONE status for its invalidation_wait and will
indefinitely remain stuck.
This soft lockup does not occur when only non-zero descriptors are
submitted.In such cases, invalidation descriptors are interspersed among
wait descriptors with the status QI_IN_USE, acting as barriers. These
barriers prevent the reclaim code from mistakenly freeing descriptors
belonging to other submitters.
Considered the following example timeline:
T1 T2
========================================
ID1
WD1
while(WD1!=QI_DONE)
unlock
lock
WD1=QI_DONE* WD2
while(WD2!=QI_DONE)
unlock
lock
WD1==QI_DONE?
ID1=QI_DONE WD2=DONE*
reclaim()
ID1=FREE
WD1=FREE
WD2=FREE
unlock
soft lockup! T2 never sees QI_DONE in WD2
Where:
ID = invalidation descriptor
WD = wait descriptor
* Written by hardware
The root of the problem is that the descriptor status QI_DONE flag is used
for two conflicting purposes:
1. signal a descriptor is ready for reclaim (to be freed)
2. signal by the hardware that a wait descriptor is complete
The solution (in this patch) is state separation by using QI_FREE flag
for #1.
Once a thread's invalidation descriptors are complete, their status would
be set to QI_FREE. The reclaim_free_desc() function would then only
free descriptors marked as QI_FREE instead of those marked as
QI_DONE. This change ensures that T2 (from the previous example) will
correctly observe the completion of its invalidation_wait (marked as
QI_DONE).
CVSS Scores
SSVC
- Decision:-
Timeline
- 2024-10-21 CVE Reserved
- 2024-10-21 CVE Published
- 2024-10-21 CVE Updated
- ---------- EPSS Updated
- ---------- Exploited in Wild
- ---------- KEV Due Date
- ---------- First Exploit
CWE
CAPEC
References (7)
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Affected Vendors, Products, and Versions
Vendor | Product | Version | Other | Status | ||||||
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Vendor | Product | Version | Other | Status | <-- --> | Vendor | Product | Version | Other | Status |
Linux Search vendor "Linux" | Linux Kernel Search vendor "Linux" for product "Linux Kernel" | < 5.10.227 Search vendor "Linux" for product "Linux Kernel" and version " < 5.10.227" | en |
Affected
| ||||||
Linux Search vendor "Linux" | Linux Kernel Search vendor "Linux" for product "Linux Kernel" | < 5.15.168 Search vendor "Linux" for product "Linux Kernel" and version " < 5.15.168" | en |
Affected
| ||||||
Linux Search vendor "Linux" | Linux Kernel Search vendor "Linux" for product "Linux Kernel" | < 6.1.113 Search vendor "Linux" for product "Linux Kernel" and version " < 6.1.113" | en |
Affected
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Linux Search vendor "Linux" | Linux Kernel Search vendor "Linux" for product "Linux Kernel" | < 6.6.55 Search vendor "Linux" for product "Linux Kernel" and version " < 6.6.55" | en |
Affected
| ||||||
Linux Search vendor "Linux" | Linux Kernel Search vendor "Linux" for product "Linux Kernel" | < 6.10.14 Search vendor "Linux" for product "Linux Kernel" and version " < 6.10.14" | en |
Affected
| ||||||
Linux Search vendor "Linux" | Linux Kernel Search vendor "Linux" for product "Linux Kernel" | < 6.11.3 Search vendor "Linux" for product "Linux Kernel" and version " < 6.11.3" | en |
Affected
| ||||||
Linux Search vendor "Linux" | Linux Kernel Search vendor "Linux" for product "Linux Kernel" | < 6.12-rc1 Search vendor "Linux" for product "Linux Kernel" and version " < 6.12-rc1" | en |
Affected
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