On Wed, Aug 17, 2022 at 9:24 PM Kuniyuki Iwashima <kuniyu@xxxxxxxxxx> wrote:
>
> A sysctl variable bpf_jit_enable is accessed concurrently, and there is
> always a chance of data-race. So, all readers and a writer need some
> basic protection to avoid load/store-tearing.
>
> Fixes: 0a14842f5a3c ("net: filter: Just In Time compiler for x86-64")
> Signed-off-by: Kuniyuki Iwashima <kuniyu@xxxxxxxxxx>
> ---
> arch/arm/net/bpf_jit_32.c | 2 +-
> arch/arm64/net/bpf_jit_comp.c | 2 +-
> arch/mips/net/bpf_jit_comp.c | 2 +-
> arch/powerpc/net/bpf_jit_comp.c | 5 +++--
> arch/riscv/net/bpf_jit_core.c | 2 +-
> arch/s390/net/bpf_jit_comp.c | 2 +-
> arch/sparc/net/bpf_jit_comp_32.c | 5 +++--
> arch/sparc/net/bpf_jit_comp_64.c | 5 +++--
> arch/x86/net/bpf_jit_comp.c | 2 +-
> arch/x86/net/bpf_jit_comp32.c | 2 +-
> include/linux/filter.h | 2 +-
> net/core/sysctl_net_core.c | 4 ++--
> 12 files changed, 19 insertions(+), 16 deletions(-)
>
> diff --git a/arch/arm/net/bpf_jit_32.c b/arch/arm/net/bpf_jit_32.c
> index 6a1c9fca5260..4b6b62a6fdd4 100644
> --- a/arch/arm/net/bpf_jit_32.c
> +++ b/arch/arm/net/bpf_jit_32.c
> @@ -1999,7 +1999,7 @@ struct bpf_prog *bpf_int_jit_compile(struct bpf_prog *prog)
> }
> flush_icache_range((u32)header, (u32)(ctx.target + ctx.idx));
>
> - if (bpf_jit_enable > 1)
> + if (READ_ONCE(bpf_jit_enable) > 1)
Nack.
Even if the compiler decides to use single byte loads for some
odd reason there is no issue here.
