netdev - Re: [PATCH net] bpf, arm: start flushing icache range from header

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Date:	Mon, 16 Nov 2015 12:00:54 +0000
From:	Mark Rutland <mark.rutland@....com>
To:	Daniel Borkmann <daniel@...earbox.net>
Cc:	netdev@...r.kernel.org, nschichan@...ebox.fr, davem@...emloft.net,
	linux-arm-kernel@...ts.infradead.org, ast@...nel.org
Subject: Re: [PATCH net] bpf, arm: start flushing icache range from header

On Mon, Nov 16, 2015 at 11:40:55AM +0000, Mark Rutland wrote:
> On Sat, Nov 14, 2015 at 01:26:53AM +0100, Daniel Borkmann wrote:
> > During review I noticed that the icache range we're flushing should
> > start at header already and not at ctx.image.
> > 
> > Reason is that after 55309dd3d4cd ("net: bpf: arm: 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@...earbox.net>
> > Tested-by: Nicolas Schichan <nschichan@...ebox.fr>
> > Cc: Alexei Starovoitov <ast@...nel.org>
> > ---
> >  ( As arm32 fixes usually go via Dave's tree, targeting -net. )
> > 
> >  arch/arm/net/bpf_jit_32.c | 2 +-
> >  1 file changed, 1 insertion(+), 1 deletion(-)
> > 
> > diff --git a/arch/arm/net/bpf_jit_32.c b/arch/arm/net/bpf_jit_32.c
> > index 2f4b14c..591f9db 100644
> > --- a/arch/arm/net/bpf_jit_32.c
> > +++ b/arch/arm/net/bpf_jit_32.c
> > @@ -1061,7 +1061,7 @@ void bpf_jit_compile(struct bpf_prog *fp)
> >  	}
> >  	build_epilogue(&ctx);
> >  
> > -	flush_icache_range((u32)ctx.target, (u32)(ctx.target + ctx.idx));
> > +	flush_icache_range((u32)header, (u32)(ctx.target + ctx.idx));
> 
> As with the arm64 patch, doesn't this prevent us from flushing the end
> of the image? ctx.idx doesn't seem to take into account the header size.

I'd misread the patch; it is fine.

Sorry for the noise.

Mark.
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