[PATCH] bpf, arm64: start flushing icache range from header

[Mark Rutland]

On Sat, Nov 14, 2015 at 01:16:18AM +0100, Daniel Borkmann wrote:
> While recently going over ARM64's BPF code, I noticed that the icache
> range we're flushing should start at header already and not at ctx.image.
> 
> Reason is that after b569c1c622c5 ("net: bpf: arm64: address randomize
> and write protect JIT code"), we also want to make sure to flush the
> random-sized trap in front of the start of the actual program (analogous
> to x86). No operational differences from user side.
> 
> Signed-off-by: Daniel Borkmann <daniel at iogearbox.net>
> Acked-by: Zi Shen Lim <zlim.lnx at gmail.com>
> Cc: Alexei Starovoitov <ast at kernel.org>
> ---
>  ( As arm64 jit fixes seem to go via arm64 tree, sending them here. )
> 
>  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 a44e529..ee06570 100644
> --- a/arch/arm64/net/bpf_jit_comp.c
> +++ b/arch/arm64/net/bpf_jit_comp.c
> @@ -740,7 +740,7 @@ void bpf_int_jit_compile(struct bpf_prog *prog)
>  	if (bpf_jit_enable > 1)
>  		bpf_jit_dump(prog->len, image_size, 2, ctx.image);
>  
> -	bpf_flush_icache(ctx.image, ctx.image + ctx.idx);
> +	bpf_flush_icache(header, ctx.image + ctx.idx);

As far as I can see, ctx.idx doesn't take into account the size of the
header, given we zero it after bpf_jit_binary_alloc, and increment it
for each instruction.

So won't this prevent us from flushing the end of the image? Or did I
miss something?

Mark.