GHSA-J99R-J84H-CMW8
Vulnerability from github – Published: 2026-08-06 09:30 – Updated: 2026-08-06 09:30In the Linux kernel, the following vulnerability has been resolved:
dma-buf/udmabuf: skip redundant cpu sync to fix cacheline EEXIST warning
When CONFIG_DMA_API_DEBUG_SG is enabled, importing a udmabuf into a DRM driver (e.g. amdgpu for video playback in GNOME Videos / Showtime) triggers a spurious warning:
DMA-API: amdgpu 0000:03:00.0: cacheline tracking EEXIST, \ overlapping mappings aren't supported WARNING: kernel/dma/debug.c:619 at add_dma_entry+0x473/0x5f0
The call chain is:
amdgpu_cs_ioctl -> amdgpu_ttm_backend_bind -> dma_buf_map_attachment -> [udmabuf] map_udmabuf -> get_sg_table -> dma_map_sgtable(dev, sg, direction, 0) // attrs=0 -> debug_dma_map_sg -> add_dma_entry -> EEXIST
This happens because udmabuf builds a per-page scatter-gather list via sg_set_folio(). When begin_cpu_udmabuf() has already created an sg table mapped for the misc device, and an importer such as amdgpu maps the same pages for its own device via map_udmabuf(), the DMA debug infrastructure sees two active mappings whose physical addresses share cacheline boundaries and warns about the overlap.
The DMA_ATTR_SKIP_CPU_SYNC flag suppresses this check in add_dma_entry() because it signals that no CPU cache maintenance is performed at map/unmap time, making the cacheline overlap harmless.
All other major dma-buf exporters already pass this flag: - drm_gem_map_dma_buf() passes DMA_ATTR_SKIP_CPU_SYNC - amdgpu_dma_buf_map() passes DMA_ATTR_SKIP_CPU_SYNC
The CPU sync at map/unmap time is also redundant for udmabuf: begin_cpu_udmabuf() and end_cpu_udmabuf() already perform explicit cache synchronization via dma_sync_sgtable_for_cpu/device() when CPU access is requested through the dma-buf interface.
Pass DMA_ATTR_SKIP_CPU_SYNC to dma_map_sgtable() and dma_unmap_sgtable() in udmabuf to suppress the spurious warning and skip the redundant sync.
{
"affected": [],
"aliases": [
"CVE-2026-64590"
],
"database_specific": {
"cwe_ids": [],
"github_reviewed": false,
"github_reviewed_at": null,
"nvd_published_at": "2026-08-06T08:16:34Z",
"severity": null
},
"details": "In the Linux kernel, the following vulnerability has been resolved:\n\ndma-buf/udmabuf: skip redundant cpu sync to fix cacheline EEXIST warning\n\nWhen CONFIG_DMA_API_DEBUG_SG is enabled, importing a udmabuf into a DRM\ndriver (e.g. amdgpu for video playback in GNOME Videos / Showtime)\ntriggers a spurious warning:\n\n DMA-API: amdgpu 0000:03:00.0: cacheline tracking EEXIST, \\\n overlapping mappings aren\u0027t supported\n WARNING: kernel/dma/debug.c:619 at add_dma_entry+0x473/0x5f0\n\nThe call chain is:\n\n amdgpu_cs_ioctl\n -\u003e amdgpu_ttm_backend_bind\n -\u003e dma_buf_map_attachment\n -\u003e [udmabuf] map_udmabuf -\u003e get_sg_table\n -\u003e dma_map_sgtable(dev, sg, direction, 0) // attrs=0\n -\u003e debug_dma_map_sg -\u003e add_dma_entry -\u003e EEXIST\n\nThis happens because udmabuf builds a per-page scatter-gather list via\nsg_set_folio(). When begin_cpu_udmabuf() has already created an sg\ntable mapped for the misc device, and an importer such as amdgpu maps\nthe same pages for its own device via map_udmabuf(), the DMA debug\ninfrastructure sees two active mappings whose physical addresses share\ncacheline boundaries and warns about the overlap.\n\nThe DMA_ATTR_SKIP_CPU_SYNC flag suppresses this check in\nadd_dma_entry() because it signals that no CPU cache maintenance is\nperformed at map/unmap time, making the cacheline overlap harmless.\n\nAll other major dma-buf exporters already pass this flag:\n - drm_gem_map_dma_buf() passes DMA_ATTR_SKIP_CPU_SYNC\n - amdgpu_dma_buf_map() passes DMA_ATTR_SKIP_CPU_SYNC\n\nThe CPU sync at map/unmap time is also redundant for udmabuf:\nbegin_cpu_udmabuf() and end_cpu_udmabuf() already perform explicit\ncache synchronization via dma_sync_sgtable_for_cpu/device() when CPU\naccess is requested through the dma-buf interface.\n\nPass DMA_ATTR_SKIP_CPU_SYNC to dma_map_sgtable() and\ndma_unmap_sgtable() in udmabuf to suppress the spurious warning and\nskip the redundant sync.",
"id": "GHSA-j99r-j84h-cmw8",
"modified": "2026-08-06T09:30:33Z",
"published": "2026-08-06T09:30:32Z",
"references": [
{
"type": "ADVISORY",
"url": "https://nvd.nist.gov/vuln/detail/CVE-2026-64590"
},
{
"type": "WEB",
"url": "https://git.kernel.org/stable/c/0449a6583c0ee76778d314e4e82f166fc97fa9d8"
},
{
"type": "WEB",
"url": "https://git.kernel.org/stable/c/0db56e7eae932f8e2f3eb44ad1a63633d8f504f8"
},
{
"type": "WEB",
"url": "https://git.kernel.org/stable/c/34696563461c9a23177feb6d8aff43f4c0510278"
},
{
"type": "WEB",
"url": "https://git.kernel.org/stable/c/504e2b4ab97a51d56d966cd36d0997ad30b65b2d"
},
{
"type": "WEB",
"url": "https://git.kernel.org/stable/c/d6552f5cff795d60e629f37513ecf23d88fd2f82"
}
],
"schema_version": "1.4.0",
"severity": []
}
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