{"id":"CVE-2026-63794","aliases":[],"url":"https://o3.security/vulnerability/CVE-2026-63794","summary":"KVM: SVM: Fix page overflow in sev_dbg_crypt() for ENCRYPT path","details":"In the Linux kernel, the following vulnerability has been resolved:\n\nKVM: SVM: Fix page overflow in sev_dbg_crypt() for ENCRYPT path\n\nIn sev_dbg_crypt(), the per-iteration transfer length is bounded by\nthe source page offset (PAGE_SIZE - s_off) but not by the destination\npage offset (PAGE_SIZE - d_off).  When d_off > s_off, the encrypt\npath (__sev_dbg_encrypt_user) performs a read-modify-write using a\nsingle-page intermediate buffer (dst_tpage):\n\n  1. __sev_dbg_decrypt() expands the size to round_up(len + (d_off & 15), 16)\n     before issuing the PSP command.  If len + (d_off & 15) > PAGE_SIZE,\n     the PSP writes beyond the end of the 4096-byte dst_tpage allocation.\n\n  2. The subsequent memcpy()/copy_from_user() into\n     page_address(dst_tpage) + (d_off & 15) of 'len' bytes overflows\n     by up to 15 bytes under the same condition.\n\nTrigger example: s_off = 0, d_off = 1, debug.len = PAGE_SIZE -\nthe PSP is instructed to write round_up(4097, 16) = 4112 bytes to\na 4096-byte buffer.\n\nFix by also bounding len by (PAGE_SIZE - d_off), the same check that\nsev_send_update_data() already performs for its single-page guest\nregion.\n\n ==================================================================\n BUG: KASAN: slab-use-after-free in sev_dbg_crypt+0x993/0xd10 [kvm_amd]\n Write of size 4095 at addr ff110062293bb009 by task sev_dbg_test/228214\n\n CPU: 96 UID: 0 PID: 228214 Comm: sev_dbg_test Tainted: G     U  W           7.0.0-smp--5ce9b0c48211-dbg #156 PREEMPTLAZY\n Tainted: [U]=USER, [W]=WARN\n Hardware name: Google Astoria/astoria, BIOS 0.20250817.1-0 08/25/2025\n Call Trace:\n  <TASK>\n  dump_stack_lvl+0x54/0x70\n  print_report+0xbc/0x260\n  kasan_report+0xa2/0xd0\n  kasan_check_range+0x25f/0x2c0\n  __asan_memcpy+0x40/0x70\n  sev_dbg_crypt+0x993/0xd10 [kvm_amd]\n  sev_mem_enc_ioctl+0x33c/0x450 [kvm_amd]\n  kvm_vm_ioctl+0x65d/0x6d0 [kvm]\n  __se_sys_ioctl+0xb2/0x100\n  do_syscall_64+0xe8/0x870\n  entry_SYSCALL_64_after_hwframe+0x4b/0x53\n  </TASK>\n\n The buggy address belongs to the physical page:\n page: refcount:1 mapcount:0 mapping:0000000000000000 index:0x7fe72b6a0 pfn:0x62293bb\n memcg:ff11000112827d82\n flags: 0x1400000000000000(node=1|zone=1)\n raw: 1400000000000000 0000000000000000 dead000000000122 0000000000000000\n raw: 00000007fe72b6a0 0000000000000000 00000001ffffffff ff11000112827d82\n page dumped because: kasan: bad access detected\n\n Memory state around the buggy address:\n  ff110062293bbf00: 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00\n  ff110062293bbf80: 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00\n >ff110062293bc000: fa fb fb fb fb fb fb fb fc fc fc fc fc fc fc fc\n                    ^\n  ff110062293bc080: fa fb fb fb fb fb fb fb fc fc fc fc fc fc fc fc\n  ff110062293bc100: fa fb fb fb fb fb fb fb fc fc fc fc fc fc fc fc\n ==================================================================\n Disabling lock debugging due to kernel taint\n\n[sean: add sample KASAN splat, Fixes, and stable@]","published":"2026-07-19T12:02:03.488Z","modified":"2026-08-18T03:30:55.786008664Z","cvss":null,"epss":null,"cisaKev":null,"exploitsKnown":0,"affectedPackages":[{"ecosystem":"Linux","name":"Kernel","fixedVersion":"5.10.260"}],"fix":null,"references":[{"type":"WEB","url":"https://git.kernel.org/stable/c/2753a097d1fe24c4351c608048612c74108aa89f"},{"type":"WEB","url":"https://git.kernel.org/stable/c/64f2449841ffc7d203183aa4c748c9c77951ecc5"},{"type":"WEB","url":"https://git.kernel.org/stable/c/720949ed666f34ff28ffdfe1471a5861d1e41fdf"},{"type":"WEB","url":"https://git.kernel.org/stable/c/78ee2d50185a037b3d2452a97f3dad69c3f7f389"},{"type":"WEB","url":"https://git.kernel.org/stable/c/889c2a9c59897ca912bf39df5bb92555a0a13df4"},{"type":"WEB","url":"https://git.kernel.org/stable/c/9349b50f4b11f135fe73b56cb2c2c872d8bc71d7"},{"type":"WEB","url":"https://git.kernel.org/stable/c/e1a0fe288dee07b7da25a71e007c1ecd1080315b"},{"type":"WEB","url":"https://git.kernel.org/stable/c/f701ae476cb92a3a3d8844bb39bb63b4512684c8"},{"type":"ADVISORY","url":"https://github.com/CVEProject/cvelistV5/tree/main/cves/2026/63xxx/CVE-2026-63794.json"},{"type":"ADVISORY","url":"https://nvd.nist.gov/vuln/detail/CVE-2026-63794"},{"type":"PACKAGE","url":"https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git"}],"provenance":{"sources":["OSV.dev","FIRST.org (EPSS)"],"lastVerified":"2026-08-18T03:30:55.786008664Z"}}