Skip to content
New issue

Have a question about this project? Sign up for a free GitHub account to open an issue and contact its maintainers and the community.

Sign up for GitHub

By clicking “Sign up for GitHub”, you agree to our terms of service and privacy statement. We’ll occasionally send you account related emails.

Already on GitHub? Sign in to your account

Jump to bottom

bpf: put bpf_link's program when link is safe to be deallocated #7997

Open
wants to merge 3 commits into
base: bpf-next_base
Choose a base branch
from
Open

bpf: put bpf_link's program when link is safe to be deallocated #7997

wants to merge 3 commits into from
+67 −20

Conversation

kernel-patches-daemon-bpf[bot]
Copy link

Pull request for series with
subject: bpf: put bpf_link's program when link is safe to be deallocated
version: 1
url: https://patchwork.kernel.org/project/netdevbpf/list/?series=905159

@kernel-patches-daemon-bpf
Copy link
Author

Upstream branch: e626a13
series: https://patchwork.kernel.org/project/netdevbpf/list/?series=905159
version: 1

@kernel-patches-daemon-bpf
Copy link
Author

Upstream branch: e626a13
series: https://patchwork.kernel.org/project/netdevbpf/list/?series=905159
version: 1

@kernel-patches-daemon-bpf
Copy link
Author

Upstream branch: e5e4799
series: https://patchwork.kernel.org/project/netdevbpf/list/?series=905159
version: 1

@kernel-patches-daemon-bpf
Copy link
Author

Upstream branch: e5e4799
series: https://patchwork.kernel.org/project/netdevbpf/list/?series=905510
version: 2

@kernel-patches-daemon-bpf
Copy link
Author

Upstream branch: 4d99e50
series: https://patchwork.kernel.org/project/netdevbpf/list/?series=905510
version: 2

@kernel-patches-daemon-bpf
Copy link
Author

Upstream branch: 77017b9
series: https://patchwork.kernel.org/project/netdevbpf/list/?series=905510
version: 2

@kernel-patches-daemon-bpf
Copy link
Author

Upstream branch: f2daa5a
series: https://patchwork.kernel.org/project/netdevbpf/list/?series=905510
version: 2

@kernel-patches-daemon-bpf
Copy link
Author

Upstream branch: 9a78313
series: https://patchwork.kernel.org/project/netdevbpf/list/?series=905510
version: 2

@anakryiko
bpf: put bpf_link's program when link is safe to be deallocated
2725c21 
In general, BPF link's underlying BPF program should be considered to be
reachable through attach hook -> link -> prog chain, and, pessimistically,
we have to assume that as long as link's memory is not safe to free,
attach hook's code might hold a pointer to BPF program and use it.

As such, it's not (generally) correct to put link's program early before
waiting for RCU GPs to go through. More eager bpf_prog_put() that we
currently do is mostly correct due to BPF program's release code doing
similar RCU GP waiting, but as will be shown in the following patches,
BPF program can be non-sleepable (and, thus, reliant on only "classic"
RCU GP), while BPF link's attach hook can have sleepable semantics and
needs to be protected by RCU Tasks Trace, and for such cases BPF link
has to go through RCU Tasks Trace + "classic" RCU GPs before being
deallocated. And so, if we put BPF program early, we might free BPF
program before we free BPF link, leading to use-after-free situation.

So, this patch defers bpf_prog_put() until we are ready to perform
bpf_link's deallocation. At worst, this delays BPF program freeing by
one extra RCU GP, but that seems completely acceptable. Alternatively,
we'd need more elaborate ways to determine BPF hook, BPF link, and BPF
program lifetimes, and how they relate to each other, which seems like
an unnecessary complication.

Note, for most BPF links we still will perform eager bpf_prog_put() and
link dealloc, so for those BPF links there are no observable changes
whatsoever. Only BPF links that use deferred dealloc might notice
slightly delayed freeing of BPF programs.

Also, to reduce code and logic duplication, extract program put + link
dealloc logic into bpf_link_dealloc() helper.

Tested-by: Jordan Rife <[email protected]>
Signed-off-by: Andrii Nakryiko <[email protected]>
@anakryiko
bpf: decouple BPF link/attach hook and BPF program sleepable semantics
95b2816 
BPF link's lifecycle protection scheme depends on both BPF hook and BPF
program. If *either* of those require RCU Tasks Trace GP, then we need
to go through a chain of GPs before putting BPF program refcount and
deallocating BPF link memory.

This patch adds bpf_link-specific sleepable flag, which can be set to
true even if underlying BPF program is not sleepable itself. If either
link->sleepable or link->prog->sleepable is true, we'll go through
a chain of RCU Tasks Trace GP and RCU GP before putting BPF program and
freeing memory.

This will be used to protect BPF link for sleepable (faultable) raw
tracepoints in the next patch.

Tested-by: Jordan Rife <[email protected]>
Signed-off-by: Andrii Nakryiko <[email protected]>
@anakryiko
bpf: ensure RCU Tasks Trace GP for sleepable raw tracepoint BPF links
6425f9a 
Now that kernel supports sleepable tracepoints, the fact that
bpf_probe_unregister() is asynchronous, i.e., that it doesn't wait for
any in-flight tracepoints to conclude before returning, we now need to
delay BPF raw tp link's deallocation and bpf_prog_put() of its
underlying BPF program (regardless of program's own sleepable semantics)
until after full RCU Tasks Trace GP. With that GP over, we'll have
a guarantee that no tracepoint can reach BPF link and thus its BPF program.

We use newly added tracepoint_is_faultable() check to know when this RCU
Tasks Trace GP is necessary and utilize BPF link's own sleepable flag
passed through bpf_link_init_sleepable() initializer.

Tested-by: Jordan Rife <[email protected]>
Reported-by: Jordan Rife <[email protected]>
Fixes: a363d27cdbc2 ("tracing: Allow system call tracepoints to handle page faults")
Signed-off-by: Andrii Nakryiko <[email protected]>
@kernel-patches-daemon-bpf
Copy link
Author

Upstream branch: 1850ce1
series: https://patchwork.kernel.org/project/netdevbpf/list/?series=905510
version: 2

Sign up for free to join this conversation on GitHub. Already have an account? Sign in to comment
Reviewers
No reviews
Assignees
No one assigned
Labels
bpf-next new V2-ci-fail V2
Projects
None yet
Milestone
No milestone
Development

Successfully merging this pull request may close these issues.
1 participant
@anakryiko