Re: [PATCH] arm64: bpf: Fix UBSAN misaligned access in BPF JIT

[Xu Kuohai]

On 2/24/2026 5:31 PM, Fuad Tabba wrote:
> struct bpf_plt contains a u64 'target' field. The BPF JIT allocator
> was using an alignment of 4 bytes (sizeof(u32)), which could lead
> to the 'target' field being misaligned in the JIT buffer.
>
> Increase the alignment requirement to 8 bytes (sizeof(u64)) in
> bpf_jit_binary_pack_alloc() to guarantee proper alignment for
> struct bpf_plt.
>
> Fixes: b2ad54e1533e9 ("bpf, arm64: Implement bpf_arch_text_poke() for arm64")
> Signed-off-by: Fuad Tabba <tabba@xxxxxxxxxx>
> ---
>   arch/arm64/net/bpf_jit_comp.c | 2 +-
>   1 file changed, 1 insertion(+), 1 deletion(-)
>
> diff --git a/arch/arm64/net/bpf_jit_comp.c b/arch/arm64/net/bpf_jit_comp.c
> index 356d33c7a4ae..adf84962d579 100644
> --- a/arch/arm64/net/bpf_jit_comp.c
> +++ b/arch/arm64/net/bpf_jit_comp.c
> @@ -2119,7 +2119,7 @@ struct bpf_prog *bpf_int_jit_compile(struct bpf_prog *prog)
>   	extable_offset = round_up(prog_size + PLT_TARGET_SIZE, extable_align);
>   	image_size = extable_offset + extable_size;
>   	ro_header = bpf_jit_binary_pack_alloc(image_size, &ro_image_ptr,
> -					      sizeof(u32), &header, &image_ptr,
> +					      sizeof(u64), &header, &image_ptr,
>   					      jit_fill_hole);
>   	if (!ro_header) {
>   		prog = orig_prog;

Good catch. build_plt pads NOP instructions to ensure a 64-bit relative offset for
plt target, but it misses the alignment check for image base itself.

Acked-by: Xu Kuohai <xukuohai@xxxxxxxxxxxxxxx>

nit: Add check for base alignment in build_plt, or a comment to clarify?