Hello Amery, On Fri, Dec 20, 2024 at 11:55:29AM -0800, Amery Hung wrote: > From: Amery Hung <amery.hung@xxxxxxxxxxxxx> > > Allow a struct_ops program to return a referenced kptr if the struct_ops > operator's return type is a struct pointer. To make sure the returned > pointer continues to be valid in the kernel, several constraints are > required: > > 1) The type of the pointer must matches the return type > 2) The pointer originally comes from the kernel (not locally allocated) > 3) The pointer is in its unmodified form > > Implementation wise, a referenced kptr first needs to be allowed to _leak_ > in check_reference_leak() if it is in the return register. Then, in > check_return_code(), constraints 1-3 are checked. During struct_ops > registration, a check is also added to warn about operators with > non-struct pointer return. > > In addition, since the first user, Qdisc_ops::dequeue, allows a NULL > pointer to be returned when there is no skb to be dequeued, we will allow > a scalar value with value equals to NULL to be returned. > > In the future when there is a struct_ops user that always expects a valid > pointer to be returned from an operator, we may extend tagging to the > return value. We can tell the verifier to only allow NULL pointer return > if the return value is tagged with MAY_BE_NULL. > > Signed-off-by: Amery Hung <amery.hung@xxxxxxxxxxxxx> I feel this patchset is very useful, as Alexei shared, it can help to mark two ublk bpf aio kfunc[1] as KF_ACQ/REL for avoiding bpf aio leak. [1] https://lore.kernel.org/linux-block/20250107120417.1237392-1-tom.leiming@xxxxxxxxx/ So I try to test it with ublk bpf patchset, however, looks it fails ublk bpf selftests. And the test does succeed without applying this patch, and ublk is built as module. - apply the 1st and the 3rd(this one) patch - apply ublk bpf patchset[1] - build kernel & reboot - make -C tools/testing/selftests TARGETS=ublk run_tests make: Entering directory '/root/git/linux/tools/testing/selftests' make[1]: Entering directory '/root/git/linux/tools/testing/selftests/ublk' GEN vmlinux.h CLNG-BPF ublk_loop.bpf.o GEN-SKEL ublk_loop.skel.h CLNG-BPF ublk_null.bpf.o GEN-SKEL ublk_null.skel.h CLNG-BPF ublk_stripe.bpf.o GEN-SKEL ublk_stripe.skel.h CC ublk_bpf.o BINARY ublk_bpf rm /root/git/linux/tools/testing/selftests/ublk/ublk_bpf.o make[1]: Leaving directory '/root/git/linux/tools/testing/selftests/ublk' make[1]: Entering directory '/root/git/linux/tools/testing/selftests/ublk' TAP version 13 1..8 # timeout set to 45 # selftests: ublk: test_null_01.sh # null_01 : [PASS] ok 1 selftests: ublk: test_null_01.sh # timeout set to 45 # selftests: ublk: test_null_02.sh # libbpf: struct_ops init_kern: struct ublk_bpf_ops data is not found in struct bpf_struct_ops_ublk_bpf_ops # libbpf: failed to load object 'ublk_null.bpf.o' # fail to load bpf obj from ublk_null.bpf.o # fail to register bpf prog null ublk_null.bpf.o not ok 2 selftests: ublk: test_null_02.sh # exit=255 Thanks, Ming
