bpf, arm64: Force 8-byte alignment for JIT buffer to prevent atomic tearing

Overview

In the Linux kernel, the following vulnerability has been resolved:

bpf, arm64: Force 8-byte alignment for JIT buffer to prevent atomic tearing

struct bpf_plt contains a u64 target field. Currently, the BPF JIT allocator requests an alignment of 4 bytes (sizeof(u32)) for the JIT buffer.

Because the base address of the JIT buffer can be 4-byte aligned (e.g., ending in 0x4 or 0xc), the relative padding logic in build_plt() fails to ensure that target lands on an 8-byte boundary.

This leads to two issues:

1. UBSAN reports misaligned-access warnings when dereferencing the structure.
2. More critically, target is updated concurrently via WRITE_ONCE() in bpf_arch_text_poke() while the JIT'd code executes ldr. On arm64, 64-bit loads/stores are only guaranteed to be single-copy atomic if they are 64-bit aligned. A misaligned target risks a torn read, causing the JIT to jump to a corrupted address.

Fix this by increasing the allocation alignment requirement to 8 bytes (sizeof(u64)) in bpf_jit_binary_pack_alloc(). This anchors the base of the JIT buffer to an 8-byte boundary, allowing the relative padding math in build_plt() to correctly align the target field.

Affected

• Linux >= b2ad54e1533e91449cb2a371e034942bd7882b58 < f5a41b61b5faae1965a5a2cb55322fe8f17e3b2d
• Linux >= b2ad54e1533e91449cb2a371e034942bd7882b58 < 80ad264da02cc4aee718e799c2b79f0f834673dc
• Linux >= b2ad54e1533e91449cb2a371e034942bd7882b58 < 519b1ad91de5bf7a496f2b858e9212db6328e1de
• Linux >= b2ad54e1533e91449cb2a371e034942bd7882b58 < 66959ed481a474eaae278c7f6860a2a9b188a4d6
• Linux >= b2ad54e1533e91449cb2a371e034942bd7882b58 < ef06fd16d48704eac868441d98d4ef083d8f3d07
• Linux 6.0

Remediation

Refer to the linked advisories for vendor-supplied fixes and affected version ranges.