In the Linux kernel, the following vulnerability has been resolved:<\/p>\n
iommu\/amd: Wait for completion instead of returning early in iommu_completion_wait()<\/p>\n
need_sync is a per-IOMMU flag shared by all domains and devices behind
\nthat IOMMU. It is set whenever a command is queued with sync == true and
\ncleared when a completion-wait (CWAIT) command is queued. However, a
\ncleared need_sync only means that a covering CWAIT has been queued, not
\nthat all previously queued commands have actually completed in hardware.<\/p>\n
iommu_completion_wait() read need_sync locklessly and returned early
\nwhen it was false. This breaks the “block until all previously queued
\ncommands have completed” contract in a multi-CPU scenario:<\/p>\n
CPU2: queue inv-B => need_sync = true
\n CPU1: queue CWAIT(N); need_sync = false; then wait_on_sem(N)
\n CPU2: read need_sync == false => return 0 (no wait!)<\/p>\n
CPU2 returns without waiting for any sequence number even though its
\ninv-B may not have completed yet (CWAIT(N), queued after inv-B, has not
\nbeen signaled). CPU2 then proceeds to, for example, free page-table
\npages while the IOMMU can still walk stale translations, opening a
\nuse-after-free window. This is a logical race in the meaning of the
\nflag, not a memory-visibility issue, so barriers alone do not help.<\/p>\n
Fix it without losing the optimization of avoiding redundant CWAIT
\ncommands: take iommu->lock before testing need_sync, and when it is
\nfalse do not return early but wait for the last allocated sequence
\nnumber (cmd_sem_val). Since need_sync == false implies no sync command
\nwas queued after the last CWAIT, that CWAIT is FIFO-ordered after every
\nnot-yet-completed command, so waiting for its sequence number guarantees
\nall prior commands (possibly queued by another CPU) have completed. The
\ncommon path with pending work is unchanged and no extra hardware command
\nis issued.<\/p>\n","protected":false},"excerpt":{"rendered":"
In the Linux kernel, the following vulnerability has been resolved:<\/p>\n
iommu\/amd: Wait for completion instead of returning early in iommu_completion_wait()<\/p>\n
need_sync is a per-IOMMU flag shared by all d<\/p>\n","protected":false},"template":"","meta":[],"categories":[],"tags":[],"class_list":["post-5427","vuln","type-vuln","status-publish","hentry"],"_links":{"self":[{"href":"https:\/\/www.54iter.cn\/index.php?rest_route=\/wp\/v2\/vuln\/5427","targetHints":{"allow":["GET"]}}],"collection":[{"href":"https:\/\/www.54iter.cn\/index.php?rest_route=\/wp\/v2\/vuln"}],"about":[{"href":"https:\/\/www.54iter.cn\/index.php?rest_route=\/wp\/v2\/types\/vuln"}],"wp:attachment":[{"href":"https:\/\/www.54iter.cn\/index.php?rest_route=%2Fwp%2Fv2%2Fmedia&parent=5427"}],"wp:term":[{"taxonomy":"category","embeddable":true,"href":"https:\/\/www.54iter.cn\/index.php?rest_route=%2Fwp%2Fv2%2Fcategories&post=5427"},{"taxonomy":"post_tag","embeddable":true,"href":"https:\/\/www.54iter.cn\/index.php?rest_route=%2Fwp%2Fv2%2Ftags&post=5427"}],"curies":[{"name":"wp","href":"https:\/\/api.w.org\/{rel}","templated":true}]}}