From: Song Liu <songliubraving@fb.com>
To: Linus Torvalds <torvalds@linux-foundation.org>
Cc: Song Liu <song@kernel.org>,
Alexei Starovoitov <alexei.starovoitov@gmail.com>,
bpf <bpf@vger.kernel.org>, Linux-MM <linux-mm@kvack.org>,
Linux Kernel Mailing List <linux-kernel@vger.kernel.org>,
Alexei Starovoitov <ast@kernel.org>,
Daniel Borkmann <daniel@iogearbox.net>,
Kernel Team <Kernel-team@fb.com>,
Andrew Morton <akpm@linux-foundation.org>,
"Edgecombe, Rick P" <rick.p.edgecombe@intel.com>,
Christoph Hellwig <hch@infradead.org>,
Andrii Nakryiko <andrii@kernel.org>
Subject: Re: [PATCH bpf] bpf: invalidate unused part of bpf_prog_pack
Date: Thu, 21 Apr 2022 21:52:13 +0000 [thread overview]
Message-ID: <1A4FF473-0988-48BE-9993-0F5E9F0AAC95@fb.com> (raw)
In-Reply-To: <CAHk-=wh1mO5HdrOMTq68WHM51-=jdmQS=KipVYxS+5u3uRc5rg@mail.gmail.com>
Hi Linus,
> On Apr 21, 2022, at 2:28 PM, Linus Torvalds <torvalds@linux-foundation.org> wrote:
>
> On Thu, Apr 21, 2022 at 12:41 PM Song Liu <song@kernel.org> wrote:
>>
>> The extra logic I had in the original patch was to erase the memory
>> when a BPF program is freed. In this case, the memory will be
>> returned to the bpf_prog_pack, and stays as RO+X. Actually, I
>> am not quite sure whether we need this logic. If not, we only need
>> the much simpler version.
>
> Oh, I think it would be good to do at free time too.
>
> I just would want that to use the same function we already have for
> the allocation-time thing, instead of introducing completely new
> infrastructure. That was what looked very odd to me.
>
> Now, the _smallest_ patch would likely be to just save away that
> 'bpf_fill_ill_insns' function pointer in the 'struct bpf_prog_pack'
> thing.
[...]
>
> Why not just agree on a name - I suggest 'bpf_jit_fill_hole()' - and
> just get rid of that stupid 'bpf_jit_fill_hole_t' type name that only
> exists because of this thing?
Last night, I had a version which is about 90% same as this idea.
However, we cannot really use the same function at free time. The
huge page is RO+X at free time, but we are only zeroing out a chunk
of it. So regular memset/memcpy won’t work. Instead, we will need
something like bpf_arch_text_copy().
Thanks,
Song
next prev parent reply other threads:[~2022-04-21 21:52 UTC|newest]
Thread overview: 12+ messages / expand[flat|nested] mbox.gz Atom feed top
[not found] <20220421072212.608884-1-song@kernel.org>
2022-04-21 17:09 ` [PATCH bpf] bpf: invalidate unused part of bpf_prog_pack Linus Torvalds
2022-04-21 18:24 ` Alexei Starovoitov
2022-04-21 18:59 ` Linus Torvalds
2022-04-21 19:40 ` Song Liu
2022-04-21 21:28 ` Linus Torvalds
2022-04-21 21:52 ` Song Liu [this message]
2022-04-21 22:30 ` Linus Torvalds
2022-04-21 22:51 ` Song Liu
2022-04-21 23:10 ` Linus Torvalds
2022-04-22 1:31 ` Song Liu
2022-04-22 7:31 ` Peter Zijlstra
2022-04-23 5:25 ` Song Liu
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