GHSA-8VM9-66J5-XM27
Vulnerability from github – Published: 2026-07-19 12:30 – Updated: 2026-07-19 12:30In the Linux kernel, the following vulnerability has been resolved:
KVM: SVM: Fix page overflow in sev_dbg_crypt() for ENCRYPT path
In sev_dbg_crypt(), the per-iteration transfer length is bounded by the source page offset (PAGE_SIZE - s_off) but not by the destination page offset (PAGE_SIZE - d_off). When d_off > s_off, the encrypt path (__sev_dbg_encrypt_user) performs a read-modify-write using a single-page intermediate buffer (dst_tpage):
-
__sev_dbg_decrypt() expands the size to round_up(len + (d_off & 15), 16) before issuing the PSP command. If len + (d_off & 15) > PAGE_SIZE, the PSP writes beyond the end of the 4096-byte dst_tpage allocation.
-
The subsequent memcpy()/copy_from_user() into page_address(dst_tpage) + (d_off & 15) of 'len' bytes overflows by up to 15 bytes under the same condition.
Trigger example: s_off = 0, d_off = 1, debug.len = PAGE_SIZE - the PSP is instructed to write round_up(4097, 16) = 4112 bytes to a 4096-byte buffer.
Fix by also bounding len by (PAGE_SIZE - d_off), the same check that sev_send_update_data() already performs for its single-page guest region.
================================================================== BUG: KASAN: slab-use-after-free in sev_dbg_crypt+0x993/0xd10 [kvm_amd] Write of size 4095 at addr ff110062293bb009 by task sev_dbg_test/228214
CPU: 96 UID: 0 PID: 228214 Comm: sev_dbg_test Tainted: G U W 7.0.0-smp--5ce9b0c48211-dbg #156 PREEMPTLAZY Tainted: [U]=USER, [W]=WARN Hardware name: Google Astoria/astoria, BIOS 0.20250817.1-0 08/25/2025 Call Trace: dump_stack_lvl+0x54/0x70 print_report+0xbc/0x260 kasan_report+0xa2/0xd0 kasan_check_range+0x25f/0x2c0 __asan_memcpy+0x40/0x70 sev_dbg_crypt+0x993/0xd10 [kvm_amd] sev_mem_enc_ioctl+0x33c/0x450 [kvm_amd] kvm_vm_ioctl+0x65d/0x6d0 [kvm] __se_sys_ioctl+0xb2/0x100 do_syscall_64+0xe8/0x870 entry_SYSCALL_64_after_hwframe+0x4b/0x53
The buggy address belongs to the physical page: page: refcount:1 mapcount:0 mapping:0000000000000000 index:0x7fe72b6a0 pfn:0x62293bb memcg:ff11000112827d82 flags: 0x1400000000000000(node=1|zone=1) raw: 1400000000000000 0000000000000000 dead000000000122 0000000000000000 raw: 00000007fe72b6a0 0000000000000000 00000001ffffffff ff11000112827d82 page dumped because: kasan: bad access detected
Memory state around the buggy address: ff110062293bbf00: 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 ff110062293bbf80: 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00
ff110062293bc000: fa fb fb fb fb fb fb fb fc fc fc fc fc fc fc fc ^ ff110062293bc080: fa fb fb fb fb fb fb fb fc fc fc fc fc fc fc fc ff110062293bc100: fa fb fb fb fb fb fb fb fc fc fc fc fc fc fc fc ================================================================== Disabling lock debugging due to kernel taint
[sean: add sample KASAN splat, Fixes, and stable@]
{
"affected": [],
"aliases": [
"CVE-2026-63794"
],
"database_specific": {
"cwe_ids": [],
"github_reviewed": false,
"github_reviewed_at": null,
"nvd_published_at": "2026-07-19T12:16:51Z",
"severity": null
},
"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 \u003e 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 \u0026 15), 16)\n before issuing the PSP command. If len + (d_off \u0026 15) \u003e 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 \u0026 15) of \u0027len\u0027 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 \u003cTASK\u003e\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 \u003c/TASK\u003e\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 \u003eff110062293bc000: 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@]",
"id": "GHSA-8vm9-66j5-xm27",
"modified": "2026-07-19T12:30:23Z",
"published": "2026-07-19T12:30:23Z",
"references": [
{
"type": "ADVISORY",
"url": "https://nvd.nist.gov/vuln/detail/CVE-2026-63794"
},
{
"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"
}
],
"schema_version": "1.4.0",
"severity": []
}
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