bpf, arm: start flushing icache range from header

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 55309dd3d4 ("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 <[email protected]>
Tested-by: Nicolas Schichan <[email protected]>
Cc: Alexei Starovoitov <[email protected]>
Signed-off-by: David S. Miller <[email protected]>

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));
 
 #if __LINUX_ARM_ARCH__ < 7
 	if (ctx.imm_count)