[B, B:hwe, F, F:oem-5.6, F:oem-5.10, G][PATCH 0/2] CVE-2021-29154 - Linux kernel incorrect computation of branch displacements in BPF JIT compiler can be abused to execute arbitrary code in Kernel mode

[Marcelo Henrique Cerri]

Both fixes are needed for:
 - bionic:linux-hwe
 - focal:linux
 - focal:linux-oem-5.6
 - focal:linux-oem-5.10
 - groovy:linux

bionic:linux only needs the first patch.

As per https://www.openwall.com/lists/oss-security/2021/04/08/1 by
Piotr Krysiuk:

    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 at ...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 at ...il.com>

    # References

    CVE-2021-29154 (reserved via https://cveform.mitre.org/)

---
Piotr Krysiuk (2):
  UBUNTU: SAUCE: bpf, x86: Validate computation of branch displacements
    for x86-64
  UBUNTU: SAUCE: bpf, x86: Validate computation of branch displacements
    for x86-32

 arch/x86/net/bpf_jit_comp.c   | 11 ++++++++++-
 arch/x86/net/bpf_jit_comp32.c | 11 ++++++++++-
 2 files changed, 20 insertions(+), 2 deletions(-)

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2.25.1