diff mbox series

[v2,bpf-next,1/6] bpf: Add KF_RCU flag to bpf_refcount_acquire_impl

Message ID 20231107085639.3016113-2-davemarchevsky@fb.com (mailing list archive)
State Accepted
Commit 8a53f8c65c9fa6670fd27a8510ce8b52f244d2b9
Delegated to: BPF
Headers show
Series Allow bpf_refcount_acquire of mapval obtained via direct LD | expand

Checks

Context Check Description
bpf/vmtest-bpf-next-PR success PR summary
netdev/series_format success Posting correctly formatted
netdev/tree_selection success Clearly marked for bpf-next, async
netdev/fixes_present success Fixes tag not required for -next series
netdev/header_inline success No static functions without inline keyword in header files
netdev/build_32bit success Errors and warnings before: 1393 this patch: 1393
netdev/cc_maintainers warning 7 maintainers not CCed: jolsa@kernel.org sdf@google.com john.fastabend@gmail.com kpsingh@kernel.org song@kernel.org haoluo@google.com martin.lau@linux.dev
netdev/build_clang success Errors and warnings before: 1379 this patch: 1379
netdev/verify_signedoff success Signed-off-by tag matches author and committer
netdev/deprecated_api success None detected
netdev/check_selftest success No net selftest shell script
netdev/verify_fixes success Fixes tag looks correct
netdev/build_allmodconfig_warn success Errors and warnings before: 1421 this patch: 1421
netdev/checkpatch success total: 0 errors, 0 warnings, 0 checks, 8 lines checked
netdev/build_clang_rust success No Rust files in patch. Skipping build
netdev/kdoc success Errors and warnings before: 0 this patch: 0
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Commit Message

Dave Marchevsky Nov. 7, 2023, 8:56 a.m. UTC 
Refcounted local kptrs are kptrs to user-defined types with a
bpf_refcount field. Recent commits ([0], [1]) modified the lifetime of
refcounted local kptrs such that the underlying memory is not reused
until RCU grace period has elapsed.

Separately, verification of bpf_refcount_acquire calls currently
succeeds for MAYBE_NULL non-owning reference input, which is a problem
as bpf_refcount_acquire_impl has no handling for this case.

This patch takes advantage of aforementioned lifetime changes to tag
bpf_refcount_acquire_impl kfunc KF_RCU, thereby preventing MAYBE_NULL
input to the kfunc. The KF_RCU flag applies to all kfunc params; it's
fine for it to apply to the void *meta__ign param as that's populated by
the verifier and is tagged __ign regardless.

  [0]: commit 7e26cd12ad1c ("bpf: Use bpf_mem_free_rcu when
       bpf_obj_dropping refcounted nodes") is the actual change to
       allocation behaivor
  [1]: commit 0816b8c6bf7f ("bpf: Consider non-owning refs to refcounted
       nodes RCU protected") modified verifier understanding of
       refcounted local kptrs to match [0]'s changes

Signed-off-by: Dave Marchevsky <davemarchevsky@fb.com>
Fixes: 7c50b1cb76ac ("bpf: Add bpf_refcount_acquire kfunc")
---
 kernel/bpf/helpers.c | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)
diff mbox series

Patch

diff --git a/kernel/bpf/helpers.c b/kernel/bpf/helpers.c
index e46ac288a108..6e1874cc9c13 100644
--- a/kernel/bpf/helpers.c
+++ b/kernel/bpf/helpers.c
@@ -2515,7 +2515,7 @@  BTF_ID_FLAGS(func, bpf_obj_new_impl, KF_ACQUIRE | KF_RET_NULL)
 BTF_ID_FLAGS(func, bpf_percpu_obj_new_impl, KF_ACQUIRE | KF_RET_NULL)
 BTF_ID_FLAGS(func, bpf_obj_drop_impl, KF_RELEASE)
 BTF_ID_FLAGS(func, bpf_percpu_obj_drop_impl, KF_RELEASE)
-BTF_ID_FLAGS(func, bpf_refcount_acquire_impl, KF_ACQUIRE | KF_RET_NULL)
+BTF_ID_FLAGS(func, bpf_refcount_acquire_impl, KF_ACQUIRE | KF_RET_NULL | KF_RCU)
 BTF_ID_FLAGS(func, bpf_list_push_front_impl)
 BTF_ID_FLAGS(func, bpf_list_push_back_impl)
 BTF_ID_FLAGS(func, bpf_list_pop_front, KF_ACQUIRE | KF_RET_NULL)