From a5f7a5bb3b7f28ba7e4fa246775b29a0e5537255 Mon Sep 17 00:00:00 2001 From: Jinke Han Date: Tue, 8 Sep 2026 15:37:42 +0800 Subject: x86/kprobes: Fix crash when probing CS CALL instructions When using eBPF to probe CS CALL instructions within a function, a crash can be triggered. The eBPF tool probes offset 257 of the __hrtimer_run_queues() function: <__hrtimer_run_queues+249>: nopl 0x0(%rax,%rax,1) <__hrtimer_run_queues+254>: mov %r14,%rdi <__hrtimer_run_queues+257>: cs call <__x86_indirect_thunk_r12> <__hrtimer_run_queues+263>: mov %eax,%r12d <__hrtimer_run_queues+266>: xchg %ax,%ax <__hrtimer_run_queues+268>: mov %r13,%rdi Which triggers this crash: BUG: unable to handle page fault for address: 00000000000f41c9 #PF: supervisor write access in kernel mode #PF: error_code(0x0002) - not-present page PGD 0 P4D 0 Oops: 0002 [#1] SMP NOPTI CPU: 1 PID: 0 Comm: swapper/1 Kdump: loaded Tainted: P RIP: 0010:__hrtimer_run_queues+0x106/0x230 Note that __hrtimer_run_queues+0x106 is __hrtimer_run_queues+262, which is at the 6th byte of the above CS CALL instruction. Since the CS CALL instruction occupies 6 bytes, the exception occurred in the middle of that call instruction. The root cause is that when using eBPF tools to probe in the middle of a function, a kprobe with INT3 is used as the underlying implementation. During single-step emulation of the original CALL instruction, int3_emulate_call() assumes that the probed CALL instruction is 5 bytes long. However, the actual CS-prefixed CALL instruction occupies 6 bytes, so it constructs an incorrect exception return address. When the CPU returns from the kprobe handler, the next instruction to be executed is at the address of the last byte of that CS CALL instruction. Coincidentally, starting from that address, the CPU fetches and decodes a completely different instruction, which ultimately triggers a kernel crash. Fix the issue by using the actual instruction length obtained from the instruction decoder when constructing the exception return address, rather than relying on the hardcoded CALL_INSN_SIZE macro. [ mingo: Refined the changelog ] Fixes: 6256e668b7af ("x86/kprobes: Use int3 instead of debug trap for single-step") Suggested-by: Masami Hiramatsu (Google) Signed-off-by: Jinke Han Signed-off-by: Ingo Molnar Reviewed-by: Masami Hiramatsu (Google) Acked-by: Yafang Shao Acked-by: Borislav Petkov Cc: Peter Zijlstra Link: https://patch.msgid.link/20260908073742.GA10517@didi-ThinkCentre-M920t-N000 --- Documentation/process/cve.rst | 121 ++++++++++++++++++++++++++++++++++++++++++ 1 file changed, 121 insertions(+) create mode 100644 Documentation/process/cve.rst (limited to 'Documentation/process/cve.rst') diff --git a/Documentation/process/cve.rst b/Documentation/process/cve.rst new file mode 100644 index 000000000..5e2753eff --- /dev/null +++ b/Documentation/process/cve.rst @@ -0,0 +1,121 @@ +==== +CVEs +==== + +Common Vulnerabilities and Exposure (CVE®) numbers were developed as an +unambiguous way to identify, define, and catalog publicly disclosed +security vulnerabilities. Over time, their usefulness has declined with +regards to the kernel project, and CVE numbers were very often assigned +in inappropriate ways and for inappropriate reasons. Because of this, +the kernel development community has tended to avoid them. However, the +combination of continuing pressure to assign CVEs and other forms of +security identifiers, and ongoing abuses by individuals and companies +outside of the kernel community has made it clear that the kernel +community should have control over those assignments. + +The Linux kernel developer team does have the ability to assign CVEs for +potential Linux kernel security issues. This assignment is independent +of the :doc:`normal Linux kernel security bug reporting +process<../process/security-bugs>`. + +A list of all assigned CVEs for the Linux kernel can be found in the +archives of the linux-cve mailing list, as seen on +https://lore.kernel.org/linux-cve-announce/. To get notice of the +assigned CVEs, please `subscribe +`_ to that mailing list. + +Process +======= + +As part of the normal stable release process, kernel changes that are +potentially security issues are identified by the developers responsible +for CVE number assignments and have CVE numbers automatically assigned +to them. These assignments are published on the linux-cve-announce +mailing list as announcements on a frequent basis. + +Note, due to the layer at which the Linux kernel is in a system, almost +any bug might be exploitable to compromise the security of the kernel, +but the possibility of exploitation is often not evident when the bug is +fixed. Because of this, the CVE assignment team is overly cautious and +assign CVE numbers to any bugfix that they identify. This +explains the seemingly large number of CVEs that are issued by the Linux +kernel team. + +If the CVE assignment team misses a specific fix that any user feels +should have a CVE assigned to it, please email them at +and the team there will work with you on it. Note that no potential +security issues should be sent to this alias, it is ONLY for assignment +of CVEs for fixes that are already in released kernel trees. If you +feel you have found an unfixed security issue, please follow the +:doc:`normal Linux kernel security bug reporting +process<../process/security-bugs>`. + +No CVEs will be automatically assigned for unfixed security issues in +the Linux kernel; assignment will only automatically happen after a fix +is available and applied to a stable kernel tree, and it will be tracked +that way by the git commit id of the original fix. If anyone wishes to +have a CVE assigned before an issue is resolved with a commit, please +contact the kernel CVE assignment team at to get an +identifier assigned from their batch of reserved identifiers. + +No CVEs will be assigned for any issue found in a version of the kernel +that is not currently being actively supported by the Stable/LTS kernel +team. A list of the currently supported kernel branches can be found at +https://kernel.org/releases.html + +Disputes of assigned CVEs +========================= + +The authority to dispute or modify an assigned CVE for a specific kernel +change lies solely with the maintainers of the relevant subsystem +affected. This principle ensures a high degree of accuracy and +accountability in vulnerability reporting. Only those individuals with +deep expertise and intimate knowledge of the subsystem can effectively +assess the validity and scope of a reported vulnerability and determine +its appropriate CVE designation. Any attempt to modify or dispute a CVE +outside of this designated authority could lead to confusion, inaccurate +reporting, and ultimately, compromised systems. + +Invalid CVEs +============ + +If a security issue is found in a Linux kernel that is only supported by +a Linux distribution due to the changes that have been made by that +distribution, or due to the distribution supporting a kernel version +that is no longer one of the kernel.org supported releases, then a CVE +can not be assigned by the Linux kernel CVE team, and must be asked for +from that Linux distribution itself. + +Any CVE that is assigned against the Linux kernel for an actively +supported kernel version, by any group other than the kernel assignment +CVE team should not be treated as a valid CVE. Please notify the +kernel CVE assignment team at so that they can work to +invalidate such entries through the CNA remediation process. + +Applicability of specific CVEs +============================== + +As the Linux kernel can be used in many different ways, with many +different ways of accessing it by external users, or no access at all, +the applicability of any specific CVE is up to the user of Linux to +determine, it is not up to the CVE assignment team. Please do not +contact us to attempt to determine the applicability of any specific +CVE. + +Also, as the source tree is so large, and any one system only uses a +small subset of the source tree, any users of Linux should be aware that +large numbers of assigned CVEs are not relevant for their systems. + +In short, we do not know your use case, and we do not know what portions +of the kernel that you use, so there is no way for us to determine if a +specific CVE is relevant for your system. + +As always, it is best to take all released kernel changes, as they are +tested together in a unified whole by many community members, and not as +individual cherry-picked changes. Also note that for many bugs, the +solution to the overall problem is not found in a single change, but by +the sum of many fixes on top of each other. Ideally CVEs will be +assigned to all fixes for all issues, but sometimes we will fail to +notice fixes, therefore assume that some changes without a CVE assigned +might be relevant to take. + -- cgit v1.3.1