Affected: Alpaquita:stream: linux-lts

In the Linux kernel, the following vulnerability has been resolved:

x86/mm/pat: Take cpa_lock around large-page collapse

Loading and unloading modules concurrently on several CPUs on a KASAN build, with a short delay injected at the CPA page-table lookup to widen the window, faults within minutes:

BUG: KASAN: use-after-free in __change_page_attr+0x7cc/0x7e0 Write of size 8 at addr ffff888181139718 by task modprobe ... The buggy address belongs to the physical page: pfn:0x181139 ... page_type: f2(table)

cpa_collapse_large_pages() rebuilds a leaf PMD from its 4K PTEs and frees the old PTE-table pages, while __change_page_attr() fetches a PTE pointer from a lockless lookup_address_in_pgd_attr() and writes it with set_pte_atomic() only later. When module text is served from a shared large ROX mapping the two run on the same PMD:

CPU A (module load) CPU B (module finalize) ------------------- ----------------------- execmem_make_temp_rw set_memory_nx __change_page_attr split 2M -> 4K table P kpte = &P[i] (lockless) execmem_restore_rox set_memory_rox (CPA_COLLAPSE) cpa_collapse_large_pages rebuild leaf PMD flush_tlb_all pagetable_free(P) set_pte_atomic(kpte, ...) -> writes into freed P…

In the Linux kernel, the following vulnerability has been resolved:

x86/mm/pat: Take cpa_lock around large-page collapse

Loading and unloading modules concurrently on several CPUs on a KASAN build, with a short delay injected at the CPA page-table lookup to widen the window, faults within minutes:

BUG: KASAN: use-after-free in __change_page_attr+0x7cc/0x7e0 Write of size 8 at addr ffff888181139718 by task modprobe ... The buggy address belongs to the physical page: pfn:0x181139 ... page_type: f2(table)

cpa_collapse_large_pages() rebuilds a leaf PMD from its 4K PTEs and frees the old PTE-table pages, while __change_page_attr() fetches a PTE pointer from a lockless lookup_address_in_pgd_attr() and writes it with set_pte_atomic() only later. When module text is served from a shared large ROX mapping the two run on the same PMD:

CPU A (module load) CPU B (module finalize) ------------------- ----------------------- execmem_make_temp_rw set_memory_nx __change_page_attr split 2M -> 4K table P kpte = &P[i] (lockless) execmem_restore_rox set_memory_rox (CPA_COLLAPSE) cpa_collapse_large_pages rebuild leaf PMD flush_tlb_all pagetable_free(P) set_pte_atomic(kpte, ...) -> writes into freed P…

kernel-devel-7.2.8-1.1 on GA media

Affected: Ubuntu:16.04:LTS: linux-hwe-edge, Ubuntu:18.04:LTS: linux-aws-5.0, Ubuntu:18.04:LTS: linux-aws-5.3, Ubuntu:18.04:LTS: linux-azure, Ubuntu:18.04:LTS: linux-azure-5.3, Ubuntu:18.04:LTS: linux-azure-edge, Ubuntu:18.04:LTS: linux-gcp, Ubuntu:18.04:LTS: linux-gcp-5.3, Ubuntu:18.04:LTS: linux-gke-4.15, Ubuntu:18.04:LTS: linux-gke-5.4 and 120 more

In the Linux kernel, the following vulnerability has been resolved: x86/mm/pat: Take cpa_lock around large-page collapse Loading and unloading modules concurrently on several CPUs on a KASAN build, with a short delay injected at the CPA page-table lookup to widen the window, faults within minutes: BUG: KASAN: use-after-free in __change_page_attr+0x7cc/0x7e0 Write of size 8 at addr ffff888181139718 by task modprobe ... The buggy address belongs to the physical page: pfn:0x181139 ... page_type: f2(table) cpa_collapse_large_pages() rebuilds a leaf PMD from its 4K PTEs and frees the old PTE-table pages, while __change_page_attr() fetches a PTE pointer from a lockless lookup_address_in_pgd_attr() and writes it with set_pte_atomic() only later. When module text is served from a shared large ROX mapping the two run on the same PMD: CPU A (module load) CPU B (module finalize) ------------------- ----------------------- execmem_make_temp_rw set_memory_nx __change_page_attr split 2M -> 4K table P kpte = &P[i] (lockless) execmem_restore_rox set_memory_rox (CPA_COLLAPSE) cpa_collapse_large_pages rebuild leaf PMD flush_tlb_all pagetable_free(P) set_pte_atomic(kpte, ...) -> writes into freed P P is…