{"id":"CVE-2025-38261","summary":"riscv: save the SR_SUM status over switches","details":"In the Linux kernel, the following vulnerability has been resolved:\n\nriscv: save the SR_SUM status over switches\n\nWhen threads/tasks are switched we need to ensure the old execution's\nSR_SUM state is saved and the new thread has the old SR_SUM state\nrestored.\n\nThe issue was seen under heavy load especially with the syz-stress tool\nrunning, with crashes as follows in schedule_tail:\n\nUnable to handle kernel access to user memory without uaccess routines\nat virtual address 000000002749f0d0\nOops [#1]\nModules linked in:\nCPU: 1 PID: 4875 Comm: syz-executor.0 Not tainted\n5.12.0-rc2-syzkaller-00467-g0d7588ab9ef9 #0\nHardware name: riscv-virtio,qemu (DT)\nepc : schedule_tail+0x72/0xb2 kernel/sched/core.c:4264\n ra : task_pid_vnr include/linux/sched.h:1421 [inline]\n ra : schedule_tail+0x70/0xb2 kernel/sched/core.c:4264\nepc : ffffffe00008c8b0 ra : ffffffe00008c8ae sp : ffffffe025d17ec0\n gp : ffffffe005d25378 tp : ffffffe00f0d0000 t0 : 0000000000000000\n t1 : 0000000000000001 t2 : 00000000000f4240 s0 : ffffffe025d17ee0\n s1 : 000000002749f0d0 a0 : 000000000000002a a1 : 0000000000000003\n a2 : 1ffffffc0cfac500 a3 : ffffffe0000c80cc a4 : 5ae9db91c19bbe00\n a5 : 0000000000000000 a6 : 0000000000f00000 a7 : ffffffe000082eba\n s2 : 0000000000040000 s3 : ffffffe00eef96c0 s4 : ffffffe022c77fe0\n s5 : 0000000000004000 s6 : ffffffe067d74e00 s7 : ffffffe067d74850\n s8 : ffffffe067d73e18 s9 : ffffffe067d74e00 s10: ffffffe00eef96e8\n s11: 000000ae6cdf8368 t3 : 5ae9db91c19bbe00 t4 : ffffffc4043cafb2\n t5 : ffffffc4043cafba t6 : 0000000000040000\nstatus: 0000000000000120 badaddr: 000000002749f0d0 cause:\n000000000000000f\nCall Trace:\n[\u003cffffffe00008c8b0\u003e] schedule_tail+0x72/0xb2 kernel/sched/core.c:4264\n[\u003cffffffe000005570\u003e] ret_from_exception+0x0/0x14\nDumping ftrace buffer:\n   (ftrace buffer empty)\n---[ end trace b5f8f9231dc87dda ]---\n\nThe issue comes from the put_user() in schedule_tail\n(kernel/sched/core.c) doing the following:\n\nasmlinkage __visible void schedule_tail(struct task_struct *prev)\n{\n...\n        if (current-\u003eset_child_tid)\n                put_user(task_pid_vnr(current), current-\u003eset_child_tid);\n...\n}\n\nthe put_user() macro causes the code sequence to come out as follows:\n\n1:\t__enable_user_access()\n2:\treg = task_pid_vnr(current);\n3:\t*current-\u003eset_child_tid = reg;\n4:\t__disable_user_access()\n\nThe problem is that we may have a sleeping function as argument which\ncould clear SR_SUM causing the panic above. This was fixed by\nevaluating the argument of the put_user() macro outside the user-enabled\nsection in commit 285a76bb2cf5 (\"riscv: evaluate put_user() arg before\nenabling user access\")\"\n\nIn order for riscv to take advantage of unsafe_get/put_XXX() macros and\nto avoid the same issue we had with put_user() and sleeping functions we\nmust ensure code flow can go through switch_to() from within a region of\ncode with SR_SUM enabled and come back with SR_SUM still enabled. This\npatch addresses the problem allowing future work to enable full use of\nunsafe_get/put_XXX() macros without needing to take a CSR bit flip cost\non every access. Make switch_to() save and restore SR_SUM.","modified":"2026-04-02T12:47:54.268418Z","published":"2025-07-09T10:42:36.810Z","related":["CGA-3p9f-g7vc-5982"],"database_specific":{"osv_generated_from":"https://github.com/CVEProject/cvelistV5/tree/main/cves/2025/38xxx/CVE-2025-38261.json","cna_assigner":"Linux"},"references":[{"type":"WEB","url":"https://git.kernel.org/stable/c/69ea599a8dab93a620c92c255be4239a06290a77"},{"type":"WEB","url":"https://git.kernel.org/stable/c/788aa64c01f1262310b4c1fb827a36df170d86ea"},{"type":"ADVISORY","url":"https://github.com/CVEProject/cvelistV5/tree/main/cves/2025/38xxx/CVE-2025-38261.json"},{"type":"ADVISORY","url":"https://nvd.nist.gov/vuln/detail/CVE-2025-38261"},{"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":"76d2a0493a17d4c8ecc781366850c3c4f8e1a446"},{"fixed":"69ea599a8dab93a620c92c255be4239a06290a77"},{"fixed":"788aa64c01f1262310b4c1fb827a36df170d86ea"}]}],"database_specific":{"source":"https://storage.googleapis.com/cve-osv-conversion/osv-output/CVE-2025-38261.json"}}],"schema_version":"1.7.5"}