Re: [PATCH 1/2] bpf: fix userspace access for bpf_probe_read{, str}()

[Sasha Levin <sashal@kernel.org>]

On Mon, Mar 29, 2021 at 01:58:21PM +0300, Zidenberg, Tsahi wrote:
>commit 8d92db5c04d10381f4db70ed99b1b576f5db18a7 upstream.
>
>This is an adaptation of parts from above commit to kernel 5.4.

This is very different from the upstream commit, let's not annotate it
as that commit.

>bpf_probe_read{,str}() BPF helpers are broken on arm64, where user
>addresses cannot be accessed with normal kernelspace access.
>
>Upstream solution got into v5.8 and cannot directly be cherry picked. We
>implement the same mechanism in kernel 5.4.
>
>Detection is only enabled for machines with non-overlapping address spaces
>using CONFIG_ARCH_HAS_NON_OVERLAPPING_ADDRESS_SPACE from commits:
>commit 0ebeea8ca8a4 ("bpf: Restrict bpf_probe_read{, str}() only to archs where they work")
>commit d195b1d1d119 ("powerpc/bpf: Enable bpf_probe_read{, str}() on powerpc again")
>
>To generally fix the issue, upstream includes new BPF helpers:
>bpf_probe_read_{user,kernel}_str(). For details on them, see
>commit 6ae08ae3dea2 ("bpf: Add probe_read_{user, kernel} and probe_read_{user, kernel}_str helpers")

What stops us from taking that API back to 5.4? I took a look at the
dependencies and they don't look too scary.

Can we try that route instead? We really don't want to diverge from
upstream that much.

-- 
Thanks,
Sasha