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

[Mark Rutland]

On Mon, Nov 16, 2015 at 12:48:08PM +0100, Daniel Borkmann wrote:
> On 11/16/2015 12:39 PM, Mark Rutland wrote:
> >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?
> 
> Nope, bpf_flush_icache() takes start and end pointer ... header starts
> before ctx.image on the linear buffer. Why should this prevent us from
> flushing the end of the image?

I erroneously thought the second parameter was a size (which it clearly
isn't given it's bsed on the ctx.image pointer).

My bad, apologies for the noise.

Mark.