FKIE_CVE-2026-53360

Vulnerability from fkie_nvd - Published: 2026-07-04 12:17 - Updated: 2026-07-04 12:17
Severity
Summary
In the Linux kernel, the following vulnerability has been resolved: KVM: SEV: Require in-GHCB scratch area if GHCB v2+ is in use As per the GHCB spec, when using GHCB v2+ require the software scratch area to reside in the GHCB's shared buffer. Note, things like Page State Change (PSC) requests _rely_ on this behavior, as the guest can't provide a length when making the request, i.e. the size of the guest payload is bounded by the size of the shared buffer. Failure to force usage of the GHCB, and a slew of other flaws, lets a malicious SNP guest corrupt host kernel heap memory, and leak host heap layout information. setup_vmgexit_scratch() allocates a buffer via kvzalloc(exit_info_2), where exit_info_2 is guest-controlled. With exit_info_2=24, this yields a 24-byte allocation in kmalloc-cg-32 (32-byte slab objects). The buffer holds an 8-byte psc_hdr followed by 8-byte psc_entry structs, so only entries[0] and entries[1] are in-bounds. snp_begin_psc() validates end_entry against VMGEXIT_PSC_MAX_COUNT (253) but NOT against the actual buffer size: idx_end = hdr->end_entry; if (idx_end >= VMGEXIT_PSC_MAX_COUNT) { // checks 253, not buffer snp_complete_psc(svm, ...); return 1; } for (idx = idx_start; idx <= idx_end; idx++) { entry_start = entries[idx]; // OOB when idx >= 2 The guest sets end_entry=10+, causing the host to iterate entries[2+] which are OOB into adjacent slab objects. For each OOB entry: - The host reads 8 bytes (OOB READ / info leak oracle) - If the data passes PSC validation, __snp_complete_one_psc() writes cur_page = 1 or 512 into the entry (OOB WRITE, sev.c:3806) - If validation fails, the error response reveals whether adjacent memory is zero vs non-zero (information disclosure to guest) The guest controls allocation size (exit_info_2), entry range (cur_entry/end_entry), and can fire unlimited VMGEXITs to repeatedly hit different slab positions. By exploiting the variety of bugs, a malicious SEV-SNP guest can: - OOB read adjacent kmalloc-cg-32 objects (heap layout disclosure) - OOB write cur_page bits into adjacent objects (heap corruption) - Trigger use-after-free conditions across VMGEXITs E.g. with KASAN enabled, a single insmod of the PoC guest module produces 73 KASAN reports: BUG: KASAN: slab-out-of-bounds in snp_begin_psc+0x126/0x890 Read of size 8 at addr ffff888219ffb5e0 by task qemu-system-x86/2199 BUG: KASAN: slab-out-of-bounds in snp_begin_psc+0x468/0x890 Write of size 8 at addr ffff888351566648 by task qemu-system-x86/2199 The buggy address belongs to the object at ffff888XXXXXXXXX which belongs to the cache kmalloc-cg-32 of size 32 The buggy address is located N bytes to the right of allocated 32-byte region [ffff888XXXXXXXXX, ffff888XXXXXXXXX) Breakdown: 62 slab-out-of-bounds (reads + writes past allocation) 7 slab-use-after-free 4 use-after-free All credit to Stan for the wonderful description and reproducer! [sean: write changelog]
References
416baaa9-dc9f-4396-8d5f-8c081fb06d67https://git.kernel.org/stable/c/b328ede59ac34e7998e1eee5e5f0cc26c2a91846
416baaa9-dc9f-4396-8d5f-8c081fb06d67https://git.kernel.org/stable/c/bf9ba093fbb83c0c9a3dedd50efec29424eca2fc
416baaa9-dc9f-4396-8d5f-8c081fb06d67https://git.kernel.org/stable/c/c9b4198fbc6ed99a9da4bee9f74bb730f926c9ae
416baaa9-dc9f-4396-8d5f-8c081fb06d67https://git.kernel.org/stable/c/db3f2195d29344a3cf1e9dd9ab7f21ced7308cf7
Impacted products
Vendor Product Version
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{
  "affected": [
    {
      "affectedData": [
        {
          "defaultStatus": "unaffected",
          "product": "Linux",
          "programFiles": [
            "arch/x86/kvm/svm/sev.c"
          ],
          "repo": "https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git",
          "vendor": "Linux",
          "versions": [
            {
              "lessThan": "bf9ba093fbb83c0c9a3dedd50efec29424eca2fc",
              "status": "affected",
              "version": "4af663c2f64a8d252e690c60cf8b8abf22dc2951",
              "versionType": "git"
            },
            {
              "lessThan": "c9b4198fbc6ed99a9da4bee9f74bb730f926c9ae",
              "status": "affected",
              "version": "4af663c2f64a8d252e690c60cf8b8abf22dc2951",
              "versionType": "git"
            },
            {
              "lessThan": "b328ede59ac34e7998e1eee5e5f0cc26c2a91846",
              "status": "affected",
              "version": "4af663c2f64a8d252e690c60cf8b8abf22dc2951",
              "versionType": "git"
            },
            {
              "lessThan": "db3f2195d29344a3cf1e9dd9ab7f21ced7308cf7",
              "status": "affected",
              "version": "4af663c2f64a8d252e690c60cf8b8abf22dc2951",
              "versionType": "git"
            }
          ]
        },
        {
          "defaultStatus": "affected",
          "product": "Linux",
          "programFiles": [
            "arch/x86/kvm/svm/sev.c"
          ],
          "repo": "https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git",
          "vendor": "Linux",
          "versions": [
            {
              "status": "affected",
              "version": "6.10"
            },
            {
              "lessThan": "6.10",
              "status": "unaffected",
              "version": "0",
              "versionType": "semver"
            },
            {
              "lessThanOrEqual": "6.12.*",
              "status": "unaffected",
              "version": "6.12.93",
              "versionType": "semver"
            },
            {
              "lessThanOrEqual": "6.18.*",
              "status": "unaffected",
              "version": "6.18.35",
              "versionType": "semver"
            },
            {
              "lessThanOrEqual": "7.0.*",
              "status": "unaffected",
              "version": "7.0.12",
              "versionType": "semver"
            },
            {
              "lessThanOrEqual": "*",
              "status": "unaffected",
              "version": "7.1",
              "versionType": "original_commit_for_fix"
            }
          ]
        }
      ],
      "source": "416baaa9-dc9f-4396-8d5f-8c081fb06d67"
    }
  ],
  "cveTags": [],
  "descriptions": [
    {
      "lang": "en",
      "value": "In the Linux kernel, the following vulnerability has been resolved:\n\nKVM: SEV: Require in-GHCB scratch area if GHCB v2+ is in use\n\nAs per the GHCB spec, when using GHCB v2+ require the software scratch area\nto reside in the GHCB\u0027s shared buffer.  Note, things like Page State Change\n(PSC) requests _rely_ on this behavior, as the guest can\u0027t provide a length\nwhen making the request, i.e. the size of the guest payload is bounded by\nthe size of the shared buffer.\n\nFailure to force usage of the GHCB, and a slew of other flaws, lets a\nmalicious SNP guest corrupt host kernel heap memory, and leak host heap\nlayout information.\n\nsetup_vmgexit_scratch() allocates a buffer via kvzalloc(exit_info_2),\nwhere exit_info_2 is guest-controlled. With exit_info_2=24, this yields\na 24-byte allocation in kmalloc-cg-32 (32-byte slab objects). The buffer\nholds an 8-byte psc_hdr followed by 8-byte psc_entry structs, so only\nentries[0] and entries[1] are in-bounds.\n\nsnp_begin_psc() validates end_entry against VMGEXIT_PSC_MAX_COUNT (253)\nbut NOT against the actual buffer size:\n\n      idx_end = hdr-\u003eend_entry;\n\n      if (idx_end \u003e= VMGEXIT_PSC_MAX_COUNT) {   // checks 253, not buffer\n          snp_complete_psc(svm, ...);\n          return 1;\n      }\n\n      for (idx = idx_start; idx \u003c= idx_end; idx++) {\n          entry_start = entries[idx];           // OOB when idx \u003e= 2\n\nThe guest sets end_entry=10+, causing the host to iterate entries[2+]\nwhich are OOB into adjacent slab objects. For each OOB entry:\n\n  - The host reads 8 bytes (OOB READ / info leak oracle)\n  - If the data passes PSC validation, __snp_complete_one_psc() writes\n    cur_page = 1 or 512 into the entry (OOB WRITE, sev.c:3806)\n  - If validation fails, the error response reveals whether adjacent\n    memory is zero vs non-zero (information disclosure to guest)\n\nThe guest controls allocation size (exit_info_2), entry range\n(cur_entry/end_entry), and can fire unlimited VMGEXITs to repeatedly\nhit different slab positions.\n\nBy exploiting the variety of bugs, a malicious SEV-SNP guest can:\n    - OOB read adjacent kmalloc-cg-32 objects (heap layout disclosure)\n    - OOB write cur_page bits into adjacent objects (heap corruption)\n    - Trigger use-after-free conditions across VMGEXITs\n\nE.g. with KASAN enabled, a single insmod of the PoC guest module\nproduces 73 KASAN reports:\n\n    BUG: KASAN: slab-out-of-bounds in snp_begin_psc+0x126/0x890\n    Read of size 8 at addr ffff888219ffb5e0 by task qemu-system-x86/2199\n\n    BUG: KASAN: slab-out-of-bounds in snp_begin_psc+0x468/0x890\n    Write of size 8 at addr ffff888351566648 by task qemu-system-x86/2199\n\n    The buggy address belongs to the object at ffff888XXXXXXXXX\n     which belongs to the cache kmalloc-cg-32 of size 32\n    The buggy address is located N bytes to the right of\n     allocated 32-byte region [ffff888XXXXXXXXX, ffff888XXXXXXXXX)\n\n  Breakdown:\n    62 slab-out-of-bounds (reads + writes past allocation)\n     7 slab-use-after-free\n     4 use-after-free\n\nAll credit to Stan for the wonderful description and reproducer!\n\n[sean: write changelog]"
    }
  ],
  "id": "CVE-2026-53360",
  "lastModified": "2026-07-04T12:17:01.880",
  "metrics": {},
  "published": "2026-07-04T12:17:01.880",
  "references": [
    {
      "source": "416baaa9-dc9f-4396-8d5f-8c081fb06d67",
      "url": "https://git.kernel.org/stable/c/b328ede59ac34e7998e1eee5e5f0cc26c2a91846"
    },
    {
      "source": "416baaa9-dc9f-4396-8d5f-8c081fb06d67",
      "url": "https://git.kernel.org/stable/c/bf9ba093fbb83c0c9a3dedd50efec29424eca2fc"
    },
    {
      "source": "416baaa9-dc9f-4396-8d5f-8c081fb06d67",
      "url": "https://git.kernel.org/stable/c/c9b4198fbc6ed99a9da4bee9f74bb730f926c9ae"
    },
    {
      "source": "416baaa9-dc9f-4396-8d5f-8c081fb06d67",
      "url": "https://git.kernel.org/stable/c/db3f2195d29344a3cf1e9dd9ab7f21ced7308cf7"
    }
  ],
  "sourceIdentifier": "416baaa9-dc9f-4396-8d5f-8c081fb06d67",
  "vulnStatus": "Received"
}


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