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

BTF: arbitrary __attribute__ encoding (v3) #8429

Closed
wants to merge 11 commits into from
Closed

BTF: arbitrary __attribute__ encoding (v3) #8429

wants to merge 11 commits into from
+296 −143

Conversation

theihor
Copy link
Contributor

@theihor theihor commented Jan 30, 2025

No description provided.

Tengda Wu and others added 11 commits January 29, 2025 18:42
selftests/bpf: Fix freplace_link segfault in tailcalls prog test

Partially verified

This commit was created on GitHub.com and signed with GitHub’s verified signature.
We cannot verify signatures from co-authors, and some of the co-authors attributed to this commit require their commits to be signed.
1e49ddd 
There are two bpf_link__destroy(freplace_link) calls in
test_tailcall_bpf2bpf_freplace(). After the first bpf_link__destroy()
is called, if the following bpf_map_{update,delete}_elem() throws an
exception, it will jump to the "out" label and call bpf_link__destroy()
again, causing double free and eventually leading to a segfault.

Fix it by directly resetting freplace_link to NULL after the first
bpf_link__destroy() call.

Fixes: 021611d ("selftests/bpf: Add test to verify tailcall and freplace restrictions")
Signed-off-by: Tengda Wu <[email protected]>
Signed-off-by: Andrii Nakryiko <[email protected]>
Reviewed-by: Leon Hwang <[email protected]>
Link: https://lore.kernel.org/bpf/[email protected]
Signed-off-by: Alexei Starovoitov <[email protected]>
@guidosarducci
libbpf: Fix accessing BTF.ext core_relo header
4316819 
Update btf_ext_parse_info() to ensure the core_relo header is present
before reading its fields. This avoids a potential buffer read overflow
reported by the OSS Fuzz project.

Fixes: cf57916 ("libbpf: Support BTF.ext loading and output in either endianness")
Signed-off-by: Tony Ambardar <[email protected]>
Signed-off-by: Andrii Nakryiko <[email protected]>
Link: https://issues.oss-fuzz.com/issues/388905046
Link: https://lore.kernel.org/bpf/[email protected]
Signed-off-by: Alexei Starovoitov <[email protected]>
@guidosarducci
selftests/bpf: Fix runqslower cross-endian build
c8f02c9 
The runqslower binary from a cross-endian build currently fails to run
because the included skeleton has host endianness. Fix this by passing the
target BPF endianness to the runqslower sub-make.

Fixes: 5a63c33 ("selftests/bpf: Support cross-endian building")
Signed-off-by: Tony Ambardar <[email protected]>
Signed-off-by: Andrii Nakryiko <[email protected]>
Link: https://lore.kernel.org/bpf/[email protected]
Signed-off-by: Alexei Starovoitov <[email protected]>
@viktormalik
bpftool: Fix readlink usage in get_fd_type
5aa516d 
The `readlink(path, buf, sizeof(buf))` call reads at most sizeof(buf)
bytes and *does not* append null-terminator to buf. With respect to
that, fix two pieces in get_fd_type:

1. Change the truncation check to contain sizeof(buf) rather than
   sizeof(path).
2. Append null-terminator to buf.

Reported by Coverity.

Signed-off-by: Viktor Malik <[email protected]>
Signed-off-by: Andrii Nakryiko <[email protected]>
Reviewed-by: Quentin Monnet <[email protected]>
Link: https://lore.kernel.org/bpf/[email protected]
Signed-off-by: Alexei Starovoitov <[email protected]>
bpf: Use kallsyms to find the function name of a struct_ops's stub fu…
9af5c78 
…nction

In commit 1611603 ("bpf: Create argument information for nullable arguments."),
it introduced a "__nullable" tagging at the argument name of a
stub function. Some background on the commit:
it requires to tag the stub function instead of directly tagging
the "ops" of a struct. This is because the btf func_proto of the "ops"
does not have the argument name and the "__nullable" is tagged at
the argument name.

To find the stub function of a "ops", it currently relies on a naming
convention on the stub function "st_ops__ops_name".
e.g. tcp_congestion_ops__ssthresh. However, the new kernel
sub system implementing bpf_struct_ops have missed this and
have been surprised that the "__nullable" and the to-be-landed
"__ref" tagging was not effective.

One option would be to give a warning whenever the stub function does
not follow the naming convention, regardless if it requires arg tagging
or not.

Instead, this patch uses the kallsyms_lookup approach and removes
the requirement on the naming convention. The st_ops->cfi_stubs has
all the stub function kernel addresses. kallsyms_lookup() is used to
lookup the function name. With the function name, BTF can be used to
find the BTF func_proto. The existing "__nullable" arg name searching
logic will then fall through.

One notable change is,
if it failed in kallsyms_lookup or it failed in looking up the stub
function name from the BTF, the bpf_struct_ops registration will fail.
This is different from the previous behavior that it silently ignored
the "st_ops__ops_name" function not found error.

The "tcp_congestion_ops", "sched_ext_ops", and "hid_bpf_ops" can still be
registered successfully after this patch. There is struct_ops_maybe_null
selftest to cover the "__nullable" tagging.

Other minor changes:
1. Removed the "%s__%s" format from the pr_warn because the naming
   convention is removed.
2. The existing bpf_struct_ops_supported() is also moved earlier
   because prepare_arg_info needs to use it to decide if the
   stub function is NULL before calling the prepare_arg_info.

Cc: Tejun Heo <[email protected]>
Cc: Benjamin Tissoires <[email protected]>
Cc: Yonghong Song <[email protected]>
Cc: Amery Hung <[email protected]>
Signed-off-by: Martin KaFai Lau <[email protected]>
Reviewed-by: Amery Hung <[email protected]>
Link: https://lore.kernel.org/r/[email protected]
Signed-off-by: Alexei Starovoitov <[email protected]>
@theihor
libbpf: introduce kflag for type_tags and decl_tags in BTF
f727dbc 
Add the following functions to libbpf API:
  * btf__add_type_attr()
  * btf__add_decl_attr()

These functions allow to add to BTF the type tags and decl tags with
info->kflag set to 1. The kflag indicates that the tag directly
encodes an __attribute__ and not a normal tag.

See Documentation/bpf/btf.rst changes in the subsequent patch for
details on the semantics.

Suggested-by: Andrii Nakryiko <[email protected]>
Signed-off-by: Ihor Solodrai <[email protected]>
Reviewed-by: Alan Maguire <[email protected]>
Acked-by: Andrii Nakryiko <[email protected]>
@theihor
docs/bpf: document the semantics of BTF tags with kind_flag
c8dad92 
Explain the meaning of kind_flag in BTF type_tags and decl_tags.
Update uapi btf.h kind_flag comment to reflect the changes.

Signed-off-by: Ihor Solodrai <[email protected]>
@theihor
libbpf: check the kflag of type tags in btf_dump
b804e38 
If the kflag is set for a BTF type tag, then the tag represents an
arbitrary __attribute__. Change btf_dump accordingly.

Signed-off-by: Ihor Solodrai <[email protected]>
Reviewed-by: Alan Maguire <[email protected]>
Acked-by: Andrii Nakryiko <[email protected]>
@theihor
selftests/bpf: add a btf_dump test for type_tags
50c9aad 
Factor out common routines handling custom BTF from
test_btf_dump_incremental. Then use them in the
test_btf_dump_type_tags.

test_btf_dump_type_tags verifies that a type tag is dumped correctly
with respect to its kflag.

Signed-off-by: Ihor Solodrai <[email protected]>
Acked-by: Eduard Zingerman <[email protected]>
@theihor
bpf: allow kind_flag for BTF type and decl tags
65726fc 
BTF type tags and decl tags now may have info->kflag set to 1,
changing the semantics of the tag.

Change BTF verification to permit BTF that makes use of this feature:
  * remove kflag check in btf_decl_tag_check_meta(), as both values
    are valid
  * allow kflag to be set for BTF_KIND_TYPE_TAG type in
    btf_ref_type_check_meta()

Make sure kind_flag is NOT set when checking for specific BTF tags,
such as "kptr", "user" etc.

Modify a selftest checking for kflag in decl_tag accordingly.

Signed-off-by: Ihor Solodrai <[email protected]>
@theihor
selftests/bpf: add a BTF verification test for kflagged type_tag
Loading
Loading status checks…
02ac2b6 
Add a BTF verification test case for a type_tag with a kflag set.
Type tags with a kflag are now valid.

Add BTF_DECL_ATTR_ENC and BTF_TYPE_ATTR_ENC test helper macros,
corresponding to *_TAG_ENC.

Signed-off-by: Ihor Solodrai <[email protected]>
@kernel-patches-daemon-bpf kernel-patches-daemon-bpf bot force-pushed the bpf-next_base branch 6 times, most recently from 10fb7c0 to 30d461d Compare February 6, 2025 01:03
@kernel-patches-daemon-bpf
Copy link

Automatically cleaning up stale PR; feel free to reopen if needed

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
None yet
Projects
None yet
Milestone
No milestone
Development

Successfully merging this pull request may close these issues.

None yet
3 participants
@theihor @guidosarducci @viktormalik