CVE-2025-38434 (GCVE-0-2025-38434)
Vulnerability from cvelistv5
Published
2025-07-25 14:32
Modified
2025-07-28 04:22
Severity ?
Summary
In the Linux kernel, the following vulnerability has been resolved: Revert "riscv: Define TASK_SIZE_MAX for __access_ok()" This reverts commit ad5643cf2f69 ("riscv: Define TASK_SIZE_MAX for __access_ok()"). This commit changes TASK_SIZE_MAX to be LONG_MAX to optimize access_ok(), because the previous TASK_SIZE_MAX (default to TASK_SIZE) requires some computation. The reasoning was that all user addresses are less than LONG_MAX, and all kernel addresses are greater than LONG_MAX. Therefore access_ok() can filter kernel addresses. Addresses between TASK_SIZE and LONG_MAX are not valid user addresses, but access_ok() let them pass. That was thought to be okay, because they are not valid addresses at hardware level. Unfortunately, one case is missed: get_user_pages_fast() happily accepts addresses between TASK_SIZE and LONG_MAX. futex(), for instance, uses get_user_pages_fast(). This causes the problem reported by Robert [1]. Therefore, revert this commit. TASK_SIZE_MAX is changed to the default: TASK_SIZE. This unfortunately reduces performance, because TASK_SIZE is more expensive to compute compared to LONG_MAX. But correctness first, we can think about optimization later, if required.
References
Impacted products
Vendor Product Version
Linux Linux Version: ad5643cf2f699989daa85d909403febd6712fccb
Version: ad5643cf2f699989daa85d909403febd6712fccb
Version: ad5643cf2f699989daa85d909403febd6712fccb
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{
  "containers": {
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      "affected": [
        {
          "defaultStatus": "unaffected",
          "product": "Linux",
          "programFiles": [
            "arch/riscv/include/asm/pgtable.h"
          ],
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          "vendor": "Linux",
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          "vendor": "Linux",
          "versions": [
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              "status": "unaffected",
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              "versionType": "original_commit_for_fix"
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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\nRevert \"riscv: Define TASK_SIZE_MAX for __access_ok()\"\n\nThis reverts commit ad5643cf2f69 (\"riscv: Define TASK_SIZE_MAX for\n__access_ok()\").\n\nThis commit changes TASK_SIZE_MAX to be LONG_MAX to optimize access_ok(),\nbecause the previous TASK_SIZE_MAX (default to TASK_SIZE) requires some\ncomputation.\n\nThe reasoning was that all user addresses are less than LONG_MAX, and all\nkernel addresses are greater than LONG_MAX. Therefore access_ok() can\nfilter kernel addresses.\n\nAddresses between TASK_SIZE and LONG_MAX are not valid user addresses, but\naccess_ok() let them pass. That was thought to be okay, because they are\nnot valid addresses at hardware level.\n\nUnfortunately, one case is missed: get_user_pages_fast() happily accepts\naddresses between TASK_SIZE and LONG_MAX. futex(), for instance, uses\nget_user_pages_fast(). This causes the problem reported by Robert [1].\n\nTherefore, revert this commit. TASK_SIZE_MAX is changed to the default:\nTASK_SIZE.\n\nThis unfortunately reduces performance, because TASK_SIZE is more expensive\nto compute compared to LONG_MAX. But correctness first, we can think about\noptimization later, if required."
        }
      ],
      "providerMetadata": {
        "dateUpdated": "2025-07-28T04:22:07.336Z",
        "orgId": "416baaa9-dc9f-4396-8d5f-8c081fb06d67",
        "shortName": "Linux"
      },
      "references": [
        {
          "url": "https://git.kernel.org/stable/c/fe30c30bf3bb68d4a4d8c7c814769857b5c973e6"
        },
        {
          "url": "https://git.kernel.org/stable/c/f8b1898748dfeb4f9b67b6a6d661f354b9de3523"
        },
        {
          "url": "https://git.kernel.org/stable/c/890ba5be6335dbbbc99af14ea007befb5f83f174"
        }
      ],
      "title": "Revert \"riscv: Define TASK_SIZE_MAX for __access_ok()\"",
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    }
  },
  "cveMetadata": {
    "assignerOrgId": "416baaa9-dc9f-4396-8d5f-8c081fb06d67",
    "assignerShortName": "Linux",
    "cveId": "CVE-2025-38434",
    "datePublished": "2025-07-25T14:32:08.089Z",
    "dateReserved": "2025-04-16T04:51:24.015Z",
    "dateUpdated": "2025-07-28T04:22:07.336Z",
    "state": "PUBLISHED"
  },
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  "vulnerability-lookup:meta": {
    "nvd": "{\"cve\":{\"id\":\"CVE-2025-38434\",\"sourceIdentifier\":\"416baaa9-dc9f-4396-8d5f-8c081fb06d67\",\"published\":\"2025-07-25T15:15:28.707\",\"lastModified\":\"2025-07-25T15:29:19.837\",\"vulnStatus\":\"Awaiting Analysis\",\"cveTags\":[],\"descriptions\":[{\"lang\":\"en\",\"value\":\"In the Linux kernel, the following vulnerability has been resolved:\\n\\nRevert \\\"riscv: Define TASK_SIZE_MAX for __access_ok()\\\"\\n\\nThis reverts commit ad5643cf2f69 (\\\"riscv: Define TASK_SIZE_MAX for\\n__access_ok()\\\").\\n\\nThis commit changes TASK_SIZE_MAX to be LONG_MAX to optimize access_ok(),\\nbecause the previous TASK_SIZE_MAX (default to TASK_SIZE) requires some\\ncomputation.\\n\\nThe reasoning was that all user addresses are less than LONG_MAX, and all\\nkernel addresses are greater than LONG_MAX. Therefore access_ok() can\\nfilter kernel addresses.\\n\\nAddresses between TASK_SIZE and LONG_MAX are not valid user addresses, but\\naccess_ok() let them pass. That was thought to be okay, because they are\\nnot valid addresses at hardware level.\\n\\nUnfortunately, one case is missed: get_user_pages_fast() happily accepts\\naddresses between TASK_SIZE and LONG_MAX. futex(), for instance, uses\\nget_user_pages_fast(). This causes the problem reported by Robert [1].\\n\\nTherefore, revert this commit. TASK_SIZE_MAX is changed to the default:\\nTASK_SIZE.\\n\\nThis unfortunately reduces performance, because TASK_SIZE is more expensive\\nto compute compared to LONG_MAX. But correctness first, we can think about\\noptimization later, if required.\"},{\"lang\":\"es\",\"value\":\"En el kernel de Linux, se ha resuelto la siguiente vulnerabilidad: Revertir \\\"riscv: Define TASK_SIZE_MAX for __access_ok()\\\". Esto revierte el commit ad5643cf2f69 (\\\"riscv: Define TASK_SIZE_MAX for __access_ok()\\\"). Este commit cambia TASK_SIZE_MAX a LONG_MAX para optimizar access_ok(), ya que el valor predeterminado de TASK_SIZE_MAX (predeterminado) requiere c\u00e1lculos. El razonamiento era que todas las direcciones de usuario son menores que LONG_MAX y todas las direcciones de kernel son mayores que LONG_MAX. Por lo tanto, access_ok() puede filtrar direcciones de kernel. Las direcciones entre TASK_SIZE y LONG_MAX no son direcciones de usuario v\u00e1lidas, pero access_ok() las deja pasar. Se consider\u00f3 que esto era correcto, ya que no son direcciones v\u00e1lidas a nivel de hardware. Desafortunadamente, se omite un caso: get_user_pages_fast() acepta direcciones entre TASK_SIZE y LONG_MAX. futex(), por ejemplo, usa get_user_pages_fast(). Esto causa el problema reportado por Robert [1]. Por lo tanto, revierte este commit . TASK_SIZE_MAX se cambia al valor predeterminado: TASK_SIZE. Lamentablemente, esto reduce el rendimiento, ya que TASK_SIZE es m\u00e1s costoso de calcular que LONG_MAX. Pero primero la correcci\u00f3n; podemos pensar en la optimizaci\u00f3n m\u00e1s adelante, si es necesario.\"}],\"metrics\":{},\"references\":[{\"url\":\"https://git.kernel.org/stable/c/890ba5be6335dbbbc99af14ea007befb5f83f174\",\"source\":\"416baaa9-dc9f-4396-8d5f-8c081fb06d67\"},{\"url\":\"https://git.kernel.org/stable/c/f8b1898748dfeb4f9b67b6a6d661f354b9de3523\",\"source\":\"416baaa9-dc9f-4396-8d5f-8c081fb06d67\"},{\"url\":\"https://git.kernel.org/stable/c/fe30c30bf3bb68d4a4d8c7c814769857b5c973e6\",\"source\":\"416baaa9-dc9f-4396-8d5f-8c081fb06d67\"}]}}"
  }
}


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