Date: Thu, 8 Apr 2021 16:24:26 +0100 From: Piotr Krysiuk <piotras@...il.com> To: oss-security@...ts.openwall.com Subject: [CVE-2021-29154] Linux kernel incorrect computation of branch displacements in BPF JIT compiler can be abused to execute arbitrary code in Kernel mode An issue has been discovered in the Linux kernel that can be abused by unprivileged local users to escalate privileges. The issue is with how BPF JIT compilers for some architectures compute branch displacements when generating machine code. This can be abused to craft anomalous machine code and execute it in the Kernel mode, where the control flow is hijacked to execute unsafe code. I developed PoCs for x86-64 and x86-32 architectures to demonstrate shellcode execution in Kernel mode by unprivileged local users. One of these PoCs has been shared privately with <security@...nel.org> to assist with fix development. Patches to mitigate the issue for x86-64 and x86-32 architectures are available. These patches do not attempt to correct the underlying algorithm and instead assert that all computations were performed correctly, such that all unsafe inputs are rejected. The patches were published via BPF subsystem public git repository: * https://git.kernel.org/pub/scm/linux/kernel/git/bpf/bpf.git/patch/?id=e4d4d456436bfb2fe412ee2cd489f7658449b098 * https://git.kernel.org/pub/scm/linux/kernel/git/bpf/bpf.git/patch/?id=26f55a59dc65ff77cd1c4b37991e26497fc68049 # Discoverer Piotr Krysiuk <piotras@...il.com> # References CVE-2021-29154 (reserved via https://cveform.mitre.org/)
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