[PATCH 6.18.y 0/6] cBPF JIT spray hardening

[Pawan Gupta]

Hi,

These backports harden BPF JIT against spectre-v2 class of attacks. Without
a predictor flush, execution of new BPF program may use stale prediction
left behind by the freed one.

To avoid this, issue an IBPB flush on all CPUs on JIT program allocation.
The flush is conditional to spectre-v2 mitigation applied.

Patch 1-2: Adds the predictor flush hook and enables it on x86 via IBPB.

	  bpf: Support for hardening against JIT spraying
	  x86/bugs: Enable IBPB flush on BPF JIT allocation

Patch 3-6: Narrow the flush to only unprivileged JIT allocations
	   to avoid redundant flushes. Also adds pack-selection changes
	   that minimizes flushes.

	  bpf: Restrict JIT predictor flush to cBPF
	  bpf: Skip redundant IBPB in pack allocator
	  bpf: Prefer packs that won't trigger an IBPB flush on allocation
	  bpf: Prefer dirty packs for eBPF allocations

Patches 1 & 2 had minor header conflicts. Patch 3 had a few conflicts in
bpf_int_jit_compile(), majorly loongarch bpf_int_jit_compile() doesn't use
pack allocator, dropped was_classic hunk.

x86 builds and boots fine in a VM. I don't have build infra for other
arches, relying on the bots for the builds.

---
Pawan Gupta (6):
      bpf: Support for hardening against JIT spraying
      x86/bugs: Enable IBPB flush on BPF JIT allocation
      bpf: Restrict JIT predictor flush to cBPF
      bpf: Skip redundant IBPB in pack allocator
      bpf: Prefer packs that won't trigger an IBPB flush on allocation
      bpf: Prefer dirty packs for eBPF allocations

 arch/arm64/net/bpf_jit_comp.c        |  4 +--
 arch/loongarch/net/bpf_jit.c         |  2 +-
 arch/powerpc/net/bpf_jit_comp.c      |  4 +--
 arch/riscv/net/bpf_jit_comp64.c      |  2 +-
 arch/riscv/net/bpf_jit_core.c        |  3 +-
 arch/x86/include/asm/nospec-branch.h |  4 +++
 arch/x86/kernel/cpu/bugs.c           | 50 +++++++++++++++++++++++---
 arch/x86/net/bpf_jit_comp.c          |  5 +--
 include/linux/filter.h               | 15 ++++++--
 kernel/bpf/core.c                    | 68 ++++++++++++++++++++++++++++++++----
 kernel/bpf/dispatcher.c              |  2 +-
 11 files changed, 136 insertions(+), 23 deletions(-)
---
base-commit: e46dc0adfe39724bcf52cea47b8f9c9aed86a394
change-id: 20260713-cbpf-jit-spray-hardening-6-18-y-a028879c779c

Best regards,
--  
Pawan