{"id":"CVE-2024-26670","summary":"arm64: entry: fix ARM64_WORKAROUND_SPECULATIVE_UNPRIV_LOAD","details":"In the Linux kernel, the following vulnerability has been resolved:\n\narm64: entry: fix ARM64_WORKAROUND_SPECULATIVE_UNPRIV_LOAD\n\nCurrently the ARM64_WORKAROUND_SPECULATIVE_UNPRIV_LOAD workaround isn't\nquite right, as it is supposed to be applied after the last explicit\nmemory access, but is immediately followed by an LDR.\n\nThe ARM64_WORKAROUND_SPECULATIVE_UNPRIV_LOAD workaround is used to\nhandle Cortex-A520 erratum 2966298 and Cortex-A510 erratum 3117295,\nwhich are described in:\n\n* https://developer.arm.com/documentation/SDEN2444153/0600/?lang=en\n* https://developer.arm.com/documentation/SDEN1873361/1600/?lang=en\n\nIn both cases the workaround is described as:\n\n| If pagetable isolation is disabled, the context switch logic in the\n| kernel can be updated to execute the following sequence on affected\n| cores before exiting to EL0, and after all explicit memory accesses:\n|\n| 1. A non-shareable TLBI to any context and/or address, including\n|    unused contexts or addresses, such as a `TLBI VALE1 Xzr`.\n|\n| 2. A DSB NSH to guarantee completion of the TLBI.\n\nThe important part being that the TLBI+DSB must be placed \"after all\nexplicit memory accesses\".\n\nUnfortunately, as-implemented, the TLBI+DSB is immediately followed by\nan LDR, as we have:\n\n| alternative_if ARM64_WORKAROUND_SPECULATIVE_UNPRIV_LOAD\n| \ttlbi\tvale1, xzr\n| \tdsb\tnsh\n| alternative_else_nop_endif\n| alternative_if_not ARM64_UNMAP_KERNEL_AT_EL0\n| \tldr\tlr, [sp, #S_LR]\n| \tadd\tsp, sp, #PT_REGS_SIZE\t\t// restore sp\n| \teret\n| alternative_else_nop_endif\n|\n| [ ... KPTI exception return path ... ]\n\nThis patch fixes this by reworking the logic to place the TLBI+DSB\nimmediately before the ERET, after all explicit memory accesses.\n\nThe ERET is currently in a separate alternative block, and alternatives\ncannot be nested. To account for this, the alternative block for\nARM64_UNMAP_KERNEL_AT_EL0 is replaced with a single alternative branch\nto skip the KPTI logic, with the new shape of the logic being:\n\n| alternative_insn \"b .L_skip_tramp_exit_\\@\", nop, ARM64_UNMAP_KERNEL_AT_EL0\n| \t[ ... KPTI exception return path ... ]\n| .L_skip_tramp_exit_\\@:\n|\n| \tldr\tlr, [sp, #S_LR]\n| \tadd\tsp, sp, #PT_REGS_SIZE\t\t// restore sp\n|\n| alternative_if ARM64_WORKAROUND_SPECULATIVE_UNPRIV_LOAD\n| \ttlbi\tvale1, xzr\n| \tdsb\tnsh\n| alternative_else_nop_endif\n| \teret\n\nThe new structure means that the workaround is only applied when KPTI is\nnot in use; this is fine as noted in the documented implications of the\nerratum:\n\n| Pagetable isolation between EL0 and higher level ELs prevents the\n| issue from occurring.\n\n... and as per the workaround description quoted above, the workaround\nis only necessary \"If pagetable isolation is disabled\".","modified":"2026-04-02T10:05:24.152215Z","published":"2024-04-02T06:43:31.201Z","related":["SUSE-SU-2024:1466-1","SUSE-SU-2024:1480-1","SUSE-SU-2024:1490-1","USN-6818-2","USN-6819-2"],"database_specific":{"cna_assigner":"Linux","osv_generated_from":"https://github.com/CVEProject/cvelistV5/tree/main/cves/2024/26xxx/CVE-2024-26670.json"},"references":[{"type":"WEB","url":"https://git.kernel.org/stable/c/58eb5c07f41704464b9acc09ab0707b6769db6c0"},{"type":"WEB","url":"https://git.kernel.org/stable/c/832dd634bd1b4e3bbe9f10b9c9ba5db6f6f2b97f"},{"type":"WEB","url":"https://git.kernel.org/stable/c/baa0aaac16432019651e0d60c41cd34a0c3c3477"},{"type":"ADVISORY","url":"https://github.com/CVEProject/cvelistV5/tree/main/cves/2024/26xxx/CVE-2024-26670.json"},{"type":"ADVISORY","url":"https://nvd.nist.gov/vuln/detail/CVE-2024-26670"},{"type":"PACKAGE","url":"https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git"}],"affected":[{"ranges":[{"type":"GIT","repo":"https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git","events":[{"introduced":"471470bc7052d28ce125901877dd10e4c048e513"},{"fixed":"58eb5c07f41704464b9acc09ab0707b6769db6c0"},{"fixed":"baa0aaac16432019651e0d60c41cd34a0c3c3477"},{"fixed":"832dd634bd1b4e3bbe9f10b9c9ba5db6f6f2b97f"}]},{"type":"GIT","repo":"https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git","events":[{"introduced":"0"},{"last_affected":"6e3ae2927b432a3b7c8374f14dbc1bd9ebe4372c"},{"last_affected":"32b0a4ffcaea44a00a61e40c0d1bcc50362aee25"}]}],"database_specific":{"source":"https://storage.googleapis.com/cve-osv-conversion/osv-output/CVE-2024-26670.json"}}],"schema_version":"1.7.5","severity":[{"type":"CVSS_V3","score":"CVSS:3.1/AV:L/AC:L/PR:L/UI:N/S:U/C:N/I:N/A:H"}]}