CVE-2026-98396 (GCVE-0-2026-98396)

Vulnerability from cvelistv5 – Published: 2026-10-14 13:25 – Updated: 2026-10-19 09:18
VLAI
Title
powerpc: Do not restore KUAP in arch_exit_to_user_mode_prepare()
Summary
In the Linux kernel, the following vulnerability has been resolved: powerpc: Do not restore KUAP in arch_exit_to_user_mode_prepare() KUAP means kernel cannot touch user memory unless it explicitly is enabled. In the kernel it should stay AMR_KUAP_BLOCKED. While returning to userspace just before RFI, kernel should restore the user AMR value back. Looks like GENERIC_ENTRY might be treating arch_exit_to_user_mode_prepare() as the last architecture step before returning to userspace. commit bee25f97ad24 ("powerpc: Enable GENERIC_ENTRY feature") therefore called kuap_user_restore() from that hook. But on PowerPC that is too early. After irqentry_exit() / syscall_exit_to_user_mode() we still run platform specific exit routines. e.g. code snippets showing both exception handling and system call handling as the callers of function arch_exit_to_user_mode_prepare() which does kuap_user_restore(). The below path shows that calling kuap_user_restore() is too early when called from arch_exit_to_user_mode_prepare(). Exception handling in exceptions-64s.S ======================================= bl CFUNC(do_page_fault) ..DEFINE_INTERRUPT_HANDLER_ASYNC(do_page_fault) arch_interrupt_async_enter_prepare(regs); state = irqentry_enter(regs); instrumentation_begin(); irq_enter_rcu(); handler(regs); nap_adjust_return(regs); irq_exit_rcu(); instrumentation_end(); arch_interrupt_async_exit_prepare(regs); irqentry_exit(regs, state); <<< too early irqentry_exit_to_user_mode() __exit_to_user_mode_prepare(regs, EXIT_TO_USER_MODE_WORK_IRQ); arch_exit_to_user_mode_prepare(regs, ti_work); <<< too early b interrupt_return_srr .. bl CFUNC(interrupt_exit_user_prepare) <<< already calls kuap_user_restore prep_irq_for_enabled_exit() retry can run kernel code with IRQs on. So only when that routine is fully finished is when the user KUAP should be fully restored which interrupt_exit_user_prepare() already takes care of before returning. Similarly for system call handling in interrupt_64.S ====================================================== bl CFUNC(system_call_exception) .Lsyscall_exit: addi r4,r1,STACK_INT_FRAME_REGS li r5,0 /* !scv */ bl CFUNC(syscall_exit_prepare) .. kuap_assert_locked(); syscall_exit_to_user_mode(regs); <<< too early syscall_exit_to_user_mode_prepare(regs); <<< too early kuap_user_restore(regs); <<< already calls syscall_exit_prepare(), which can enable IRQs, replay a pending interrupt, and only then rfi. Those functions already restore KUAP immediately before rfi. Note that if we restore the user AMR too early like in the current code as shown from the code snippets above, then we get the following warning when CONFIG_PPC_KUAP_DEBUG is enabled: WARNING: arch/powerpc/include/asm/book3s/64/kup.h:293 at interrupt_exit_user_prepare+0x1a0/0x1c0 Hardware name: IBM pSeries (emulated by qemu) POWER10 (architected) TRAP: 0700 LR: c00000000000d8d4 CTR: c0000000021fe500 MSR: <SF,EE,ME,IR,DR,RI,LE> CR: 44000804 XER: 20040000 interrupt_exit_user_prepare+0x1a0/0x1c0 interrupt_return_srr_user+0x8/0x12c
Severity
No CVSS data available.
Assigner
Linux CNA under the mitre root
CNA scorecard D 53/100 over 7056 records in the last 180 days details
References
Impacted products
Vendor Product Version CPE status
Linux Linux Affected: 02565a782c1ee7e8ada38ad24a698e01d6ea9ff8 , < c8e80c19c3b9c8db83a14fab00445a6064992442 (git)
Affected: 02565a782c1ee7e8ada38ad24a698e01d6ea9ff8 , < c2549d749539487239475fbc8c614a1f9244d655 (git)
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Linux Linux Affected: 7.2
Unaffected: 0 , < 7.2 (semver)
Unaffected: 7.2.7 , ≤ 7.2.* (semver)
Unaffected: 7.3 , ≤ * (original_commit_for_fix)
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{
  "containers": {
    "cna": {
      "affected": [
        {
          "defaultStatus": "unaffected",
          "product": "Linux",
          "programFiles": [
            "arch/powerpc/include/asm/entry-common.h"
          ],
          "repo": "https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git",
          "vendor": "Linux",
          "versions": [
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              "status": "affected",
              "version": "02565a782c1ee7e8ada38ad24a698e01d6ea9ff8",
              "versionType": "git"
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          "programFiles": [
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          ],
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          "vendor": "Linux",
          "versions": [
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              "status": "affected",
              "version": "7.2"
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              "versionType": "semver"
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              "status": "unaffected",
              "version": "7.2.7",
              "versionType": "semver"
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              "status": "unaffected",
              "version": "7.3",
              "versionType": "original_commit_for_fix"
            }
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      "cpeApplicability": [
        {
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            {
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                  "criteria": "cpe:2.3:o:linux:linux_kernel:*:*:*:*:*:*:*:*",
                  "versionEndExcluding": "7.2.7",
                  "versionStartIncluding": "7.2",
                  "vulnerable": true
                },
                {
                  "criteria": "cpe:2.3:o:linux:linux_kernel:*:*:*:*:*:*:*:*",
                  "versionEndExcluding": "7.3",
                  "versionStartIncluding": "7.2",
                  "vulnerable": true
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              "negate": false,
              "operator": "OR"
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      "descriptions": [
        {
          "lang": "en",
          "value": "In the Linux kernel, the following vulnerability has been resolved:\n\npowerpc: Do not restore KUAP in arch_exit_to_user_mode_prepare()\n\nKUAP means kernel cannot touch user memory unless it explicitly is\nenabled. In the kernel it should stay AMR_KUAP_BLOCKED. While returning\nto userspace just before RFI, kernel should restore the user AMR value\nback.\n\nLooks like GENERIC_ENTRY might be treating arch_exit_to_user_mode_prepare()\nas the last architecture step before returning to userspace.\ncommit bee25f97ad24 (\"powerpc: Enable GENERIC_ENTRY feature\")\ntherefore called kuap_user_restore() from that hook. But on PowerPC that\nis too early. After irqentry_exit() / syscall_exit_to_user_mode() we\nstill run platform specific exit routines.\n\ne.g. code snippets showing both exception handling and system call\nhandling as the callers of function arch_exit_to_user_mode_prepare()\nwhich does kuap_user_restore(). The below path shows that calling\nkuap_user_restore() is too early when called from\narch_exit_to_user_mode_prepare().\n\nException handling in exceptions-64s.S\n=======================================\n\nbl\tCFUNC(do_page_fault)\n\t  ..DEFINE_INTERRUPT_HANDLER_ASYNC(do_page_fault)\n\t      arch_interrupt_async_enter_prepare(regs);\n\t      state = irqentry_enter(regs);\n\t      instrumentation_begin();\n\t      irq_enter_rcu();\n\t      handler(regs);\n\t      nap_adjust_return(regs);\n\t      irq_exit_rcu();\n\t      instrumentation_end();\n\t      arch_interrupt_async_exit_prepare(regs);\n\t      irqentry_exit(regs, state); \t\t   \u003c\u003c\u003c too early\n\t        irqentry_exit_to_user_mode()\n\t\t  __exit_to_user_mode_prepare(regs, EXIT_TO_USER_MODE_WORK_IRQ);\n\t\t    arch_exit_to_user_mode_prepare(regs, ti_work);  \u003c\u003c\u003c too early\nb\tinterrupt_return_srr\n\t\t.. bl\tCFUNC(interrupt_exit_user_prepare) \u003c\u003c\u003c already calls kuap_user_restore\n\nprep_irq_for_enabled_exit() retry can run kernel code with IRQs on. So\nonly when that routine is fully finished is when the user KUAP should be\nfully restored which interrupt_exit_user_prepare() already takes care of\nbefore returning.\n\nSimilarly for system call handling in interrupt_64.S\n======================================================\n\n\tbl\tCFUNC(system_call_exception)\n\n.Lsyscall_exit:\n\taddi\tr4,r1,STACK_INT_FRAME_REGS\n\tli\tr5,0 /* !scv */\n\tbl\tCFUNC(syscall_exit_prepare)\n\t\t  .. kuap_assert_locked();\n\t\t     syscall_exit_to_user_mode(regs); \u003c\u003c\u003c too early\n\t\t       syscall_exit_to_user_mode_prepare(regs);  \u003c\u003c\u003c too early\n \t\t     kuap_user_restore(regs);         \u003c\u003c\u003c already calls\n\nsyscall_exit_prepare(), which can enable IRQs, replay a pending\ninterrupt, and only then rfi. Those functions already restore KUAP\nimmediately before rfi.\n\nNote that if we restore the user AMR too early like in the current code\nas shown from the code snippets above, then we get the following warning\nwhen CONFIG_PPC_KUAP_DEBUG is enabled:\n  WARNING: arch/powerpc/include/asm/book3s/64/kup.h:293 at interrupt_exit_user_prepare+0x1a0/0x1c0\n  Hardware name: IBM pSeries (emulated by qemu) POWER10 (architected)\n  TRAP: 0700\n  LR: c00000000000d8d4 CTR: c0000000021fe500\n  MSR: \u003cSF,EE,ME,IR,DR,RI,LE\u003e  CR: 44000804  XER: 20040000\n  interrupt_exit_user_prepare+0x1a0/0x1c0\n  interrupt_return_srr_user+0x8/0x12c"
        }
      ],
      "providerMetadata": {
        "dateUpdated": "2026-10-19T09:18:49.794Z",
        "orgId": "416baaa9-dc9f-4396-8d5f-8c081fb06d67",
        "shortName": "Linux"
      },
      "references": [
        {
          "url": "https://git.kernel.org/stable/c/c8e80c19c3b9c8db83a14fab00445a6064992442"
        },
        {
          "url": "https://git.kernel.org/stable/c/c2549d749539487239475fbc8c614a1f9244d655"
        }
      ],
      "title": "powerpc: Do not restore KUAP in arch_exit_to_user_mode_prepare()",
      "x_generator": {
        "engine": "bippy-1.2.0"
      }
    }
  },
  "cveMetadata": {
    "assignerOrgId": "416baaa9-dc9f-4396-8d5f-8c081fb06d67",
    "assignerShortName": "Linux",
    "cveId": "CVE-2026-98396",
    "datePublished": "2026-10-14T13:25:58.490Z",
    "dateReserved": "2026-09-25T10:25:14.346Z",
    "dateUpdated": "2026-10-19T09:18:49.794Z",
    "state": "PUBLISHED"
  },
  "dataType": "CVE_RECORD",
  "dataVersion": "5.2",
  "vulnerability-lookup:meta": {
    "epss": {
      "cve": "CVE-2026-98396",
      "date": "2026-10-24",
      "epss": "0.00198",
      "percentile": "0.09005"
    },
    "nvd": {
      "cve": {
        "affected": [
          {
            "affectedData": [
              {
                "defaultStatus": "unaffected",
                "product": "Linux",
                "programFiles": [
                  "arch/powerpc/include/asm/entry-common.h"
                ],
                "repo": "https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git",
                "vendor": "Linux",
                "versions": [
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                    "lessThan": "c8e80c19c3b9c8db83a14fab00445a6064992442",
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                    "versionType": "git"
                  },
                  {
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                    "status": "affected",
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                    "versionType": "git"
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                ]
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              {
                "defaultStatus": "affected",
                "product": "Linux",
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                  "arch/powerpc/include/asm/entry-common.h"
                ],
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                "vendor": "Linux",
                "versions": [
                  {
                    "status": "affected",
                    "version": "7.2"
                  },
                  {
                    "lessThan": "7.2",
                    "status": "unaffected",
                    "version": "0",
                    "versionType": "semver"
                  },
                  {
                    "lessThanOrEqual": "7.2.*",
                    "status": "unaffected",
                    "version": "7.2.7",
                    "versionType": "semver"
                  },
                  {
                    "lessThanOrEqual": "*",
                    "status": "unaffected",
                    "version": "7.3",
                    "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\npowerpc: Do not restore KUAP in arch_exit_to_user_mode_prepare()\n\nKUAP means kernel cannot touch user memory unless it explicitly is\nenabled. In the kernel it should stay AMR_KUAP_BLOCKED. While returning\nto userspace just before RFI, kernel should restore the user AMR value\nback.\n\nLooks like GENERIC_ENTRY might be treating arch_exit_to_user_mode_prepare()\nas the last architecture step before returning to userspace.\ncommit bee25f97ad24 (\"powerpc: Enable GENERIC_ENTRY feature\")\ntherefore called kuap_user_restore() from that hook. But on PowerPC that\nis too early. After irqentry_exit() / syscall_exit_to_user_mode() we\nstill run platform specific exit routines.\n\ne.g. code snippets showing both exception handling and system call\nhandling as the callers of function arch_exit_to_user_mode_prepare()\nwhich does kuap_user_restore(). The below path shows that calling\nkuap_user_restore() is too early when called from\narch_exit_to_user_mode_prepare().\n\nException handling in exceptions-64s.S\n=======================================\n\nbl\tCFUNC(do_page_fault)\n\t  ..DEFINE_INTERRUPT_HANDLER_ASYNC(do_page_fault)\n\t      arch_interrupt_async_enter_prepare(regs);\n\t      state = irqentry_enter(regs);\n\t      instrumentation_begin();\n\t      irq_enter_rcu();\n\t      handler(regs);\n\t      nap_adjust_return(regs);\n\t      irq_exit_rcu();\n\t      instrumentation_end();\n\t      arch_interrupt_async_exit_prepare(regs);\n\t      irqentry_exit(regs, state); \t\t   \u003c\u003c\u003c too early\n\t        irqentry_exit_to_user_mode()\n\t\t  __exit_to_user_mode_prepare(regs, EXIT_TO_USER_MODE_WORK_IRQ);\n\t\t    arch_exit_to_user_mode_prepare(regs, ti_work);  \u003c\u003c\u003c too early\nb\tinterrupt_return_srr\n\t\t.. bl\tCFUNC(interrupt_exit_user_prepare) \u003c\u003c\u003c already calls kuap_user_restore\n\nprep_irq_for_enabled_exit() retry can run kernel code with IRQs on. So\nonly when that routine is fully finished is when the user KUAP should be\nfully restored which interrupt_exit_user_prepare() already takes care of\nbefore returning.\n\nSimilarly for system call handling in interrupt_64.S\n======================================================\n\n\tbl\tCFUNC(system_call_exception)\n\n.Lsyscall_exit:\n\taddi\tr4,r1,STACK_INT_FRAME_REGS\n\tli\tr5,0 /* !scv */\n\tbl\tCFUNC(syscall_exit_prepare)\n\t\t  .. kuap_assert_locked();\n\t\t     syscall_exit_to_user_mode(regs); \u003c\u003c\u003c too early\n\t\t       syscall_exit_to_user_mode_prepare(regs);  \u003c\u003c\u003c too early\n \t\t     kuap_user_restore(regs);         \u003c\u003c\u003c already calls\n\nsyscall_exit_prepare(), which can enable IRQs, replay a pending\ninterrupt, and only then rfi. Those functions already restore KUAP\nimmediately before rfi.\n\nNote that if we restore the user AMR too early like in the current code\nas shown from the code snippets above, then we get the following warning\nwhen CONFIG_PPC_KUAP_DEBUG is enabled:\n  WARNING: arch/powerpc/include/asm/book3s/64/kup.h:293 at interrupt_exit_user_prepare+0x1a0/0x1c0\n  Hardware name: IBM pSeries (emulated by qemu) POWER10 (architected)\n  TRAP: 0700\n  LR: c00000000000d8d4 CTR: c0000000021fe500\n  MSR: \u003cSF,EE,ME,IR,DR,RI,LE\u003e  CR: 44000804  XER: 20040000\n  interrupt_exit_user_prepare+0x1a0/0x1c0\n  interrupt_return_srr_user+0x8/0x12c"
          }
        ],
        "id": "CVE-2026-98396",
        "lastModified": "2026-10-19T10:18:44.197",
        "metrics": {},
        "published": "2026-10-14T14:17:50.530",
        "references": [
          {
            "source": "416baaa9-dc9f-4396-8d5f-8c081fb06d67",
            "url": "https://git.kernel.org/stable/c/c2549d749539487239475fbc8c614a1f9244d655"
          },
          {
            "source": "416baaa9-dc9f-4396-8d5f-8c081fb06d67",
            "url": "https://git.kernel.org/stable/c/c8e80c19c3b9c8db83a14fab00445a6064992442"
          }
        ],
        "sourceIdentifier": "416baaa9-dc9f-4396-8d5f-8c081fb06d67",
        "vulnStatus": "Received"
      }
    },
    "redhat_vex": {
      "aggregate_severity": "Moderate",
      "current_release_date": "2026-10-15T14:40:48+00:00",
      "cve": "CVE-2026-98396",
      "id": "CVE-2026-98396",
      "initial_release_date": "2026-10-14T00:00:00+00:00",
      "product_status:known_not_affected": "277",
      "source": "Red Hat CSAF VEX",
      "status": "final",
      "title": "kernel: powerpc: Do not restore KUAP in arch_exit_to_user_mode_prepare()",
      "url": "https://security.access.redhat.com/data/csaf/v2/vex/2026/cve-2026-98396.json",
      "version": "3"
    }
  }
}



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