From: Daniel Borkmann <daniel@iogearbox•net>
To: Alexei Starovoitov <ast@fb•com>, davem@davemloft•net
Cc: netdev@vger•kernel.org
Subject: Re: [PATCH net-next 1/2] bpf: improve htab inlining for future 32 bit jits
Date: Sat, 19 Aug 2017 02:21:28 +0200 [thread overview]
Message-ID: <59978488.9010802@iogearbox.net> (raw)
In-Reply-To: <43a2b95f-db1d-8c33-a7d6-42f8299ddcb3@fb.com>
On 08/19/2017 02:00 AM, Alexei Starovoitov wrote:
> On 8/18/17 4:51 PM, Daniel Borkmann wrote:
>> Lets future proof htab lookup inlining, commit 9015d2f59535 ("bpf:
>> inline htab_map_lookup_elem()") was making the assumption that a
>> direct call emission to __htab_map_lookup_elem() will always work
>> out for JITs. This is currently true since all JITs we have are
>> for 64 bit archs, but in case of 32 bit JITs like upcoming arm32,
>> we get a NULL pointer dereference when executing the call to
>> __htab_map_lookup_elem() since passed arguments are of a different
>> size (unsigned long vs. u64 for pointers) than what we do out of
>> BPF. Thus, lets do a proper BPF_CALL_2() declaration such that we
>> don't need to make any such assumptions.
>>
>> Reported-by: Shubham Bansal <illusionist.neo@gmail•com>
>> Signed-off-by: Daniel Borkmann <daniel@iogearbox•net>
>
> assuming on 64-bit archs the should be no perf difference
> and only increase in .text, since __htab_map_lookup_elem
> is now force inlined into a bunch of places?
> I guess that's ok, but kinda sux for 64-bit archs to pay
> such penalty because of 32-bit archs.
Yeah true, text bumps from 11k to 13k, doesn't pay off.
> May be drop always_inline and do such thing conditionally
> on 32-bit archs only?
I will guard with this instead:
diff --git a/kernel/bpf/verifier.c b/kernel/bpf/verifier.c
index 4f6e7eb..e42c096 100644
--- a/kernel/bpf/verifier.c
+++ b/kernel/bpf/verifier.c
@@ -4160,7 +4160,11 @@ static int fixup_bpf_calls(struct bpf_verifier_env *env)
continue;
}
- if (ebpf_jit_enabled() && insn->imm == BPF_FUNC_map_lookup_elem) {
+ /* BPF_EMIT_CALL() assumptions in some of the map_gen_lookup
+ * handlers are currently limited to 64 bit only.
+ */
+ if (ebpf_jit_enabled() && BITS_PER_LONG == 64 &&
+ insn->imm == BPF_FUNC_map_lookup_elem) {
map_ptr = env->insn_aux_data[i + delta].map_ptr;
if (map_ptr == BPF_MAP_PTR_POISON ||
!map_ptr->ops->map_gen_lookup)
next prev parent reply other threads:[~2017-08-19 0:21 UTC|newest]
Thread overview: 7+ messages / expand[flat|nested] mbox.gz Atom feed top
2017-08-18 23:51 [PATCH net-next 0/2] BPF inline improvements Daniel Borkmann
2017-08-18 23:51 ` [PATCH net-next 1/2] bpf: improve htab inlining for future 32 bit jits Daniel Borkmann
2017-08-19 0:00 ` Alexei Starovoitov
2017-08-19 0:21 ` Daniel Borkmann [this message]
2017-08-19 0:24 ` Alexei Starovoitov
2017-08-18 23:51 ` [PATCH net-next 2/2] bpf: inline map in map lookup functions for array and htab Daniel Borkmann
2017-08-19 0:05 ` Alexei Starovoitov
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