[PATCH bpf-next 0/3] bpf: Fix builds broken by fatal resolve_btfids warnings

[PATCH bpf-next 0/3] bpf: Fix builds broken by fatal resolve_btfids warnings

[Sasha Levin]

Commit 201a454df948 ("resolve_btfids: Fix the --fatal_warnings exit
status") makes resolve_btfids warnings fail the build again with
CONFIG_WERROR=y. That exposed BTF ID references to functions some
configs don't build. KernelCI has been seeing i386
i386_defconfig+kselftest builds fail on linux-next since next-20261015:

  WARN: resolve_btfids: unresolved symbol bpf_arena_reserve_pages
  WARN: resolve_btfids: unresolved symbol bpf_arena_free_pages
  WARN: resolve_btfids: unresolved symbol bpf_arena_alloc_pages
  Failed to generate BTF for vmlinux
  Try to disable CONFIG_DEBUG_INFO_BTF

https://files.kernelci.org/kbuild-gcc-14-i386-kselftest-6ad2315ca3f195e1aa930c8a/build.log.gz

Patch 1 drops three special_kfunc_list entries that have no users,
bpf_arena_reserve_pages among them. Patch 2 makes the remaining arena
entries depend on the condition arena.o is built with. Patch 3 fixes the
same problem for bpf_lsm_socket_sendmsg in bpf_ksock.c, which breaks
x86_64 builds with CONFIG_BPF_LSM=y and CONFIG_SECURITY_NETWORK=n.

The entries left in special_kfunc_list resolve to the same IDs as
before, and the IDs that become BTF_ID_UNUSED were already zero.

Tested by building vmlinux with CONFIG_DEBUG_INFO_BTF=y and
CONFIG_WERROR=y for i386, x86_64, and x86_64 with CONFIG_BPF_LSM=y and
both CONFIG_SECURITY_NETWORK=n and =y, and comparing special_kfunc_list
and bpf_lsm_socket_sendmsg_id before and after the series.

Sasha Levin (3):
  bpf: Drop unused entries from special_kfunc_list again
  bpf: Don't reference arena kfuncs when arena isn't built
  bpf: Fix ksock build with BPF_LSM=y and SECURITY_NETWORK=n

 kernel/bpf/verifier.c | 11 +++++------
 net/core/bpf_ksock.c  |  7 ++++++-
 2 files changed, 11 insertions(+), 7 deletions(-)


base-commit: 25bb03f0a47b622b9025a1558bf2095ec1f55d26
-- 
2.53.0

[PATCH bpf-next 1/3] bpf: Drop unused entries from special_kfunc_list again

[Sasha Levin]

Commit 6f033615ef8f ("bpf: Trim special_kfunc_list in verifier") dropped
bpf_arena_reserve_pages, bpf_stream_vprintk and bpf_stream_print_stack
from special_kfunc_list once nothing used them anymore, but commit
ab7fff217fd1 ("bpf: Check helper and kfunc arguments in one path")
brought all three back without adding any users.

Besides being dead, the bpf_arena_reserve_pages entry can't be resolved
on 32-bit and !MMU kernels, which don't build arena.o, and since commit
201a454df948 ("resolve_btfids: Fix the --fatal_warnings exit status")
the resulting resolve_btfids warning fails the build with
CONFIG_WERROR=y:

  WARN: resolve_btfids: unresolved symbol bpf_arena_reserve_pages

Drop the three entries again.

Fixes: ab7fff217fd1 ("bpf: Check helper and kfunc arguments in one path")
Assisted-by: LLM
Signed-off-by: Sasha Levin <sashal@kernel.org>
---
 kernel/bpf/verifier.c | 6 ------
 1 file changed, 6 deletions(-)

diff --git a/kernel/bpf/verifier.c b/kernel/bpf/verifier.c
index d138688468236..22f095b9dca2d 100644
--- a/kernel/bpf/verifier.c
+++ b/kernel/bpf/verifier.c
@@ -13549,10 +13549,7 @@ enum special_kfunc_type {
 	KF_bpf_call_rcu_tasks_trace,
 	KF_bpf_arena_alloc_pages,
 	KF_bpf_arena_free_pages,
-	KF_bpf_arena_reserve_pages,
 	KF_bpf_session_is_return,
-	KF_bpf_stream_vprintk,
-	KF_bpf_stream_print_stack,
 };
 
 BTF_ID_LIST(special_kfunc_list)
@@ -13644,14 +13641,11 @@ BTF_ID(func, bpf_call_rcu)
 BTF_ID(func, bpf_call_rcu_tasks_trace)
 BTF_ID(func, bpf_arena_alloc_pages)
 BTF_ID(func, bpf_arena_free_pages)
-BTF_ID(func, bpf_arena_reserve_pages)
 #ifdef CONFIG_BPF_EVENTS
 BTF_ID(func, bpf_session_is_return)
 #else
 BTF_ID_UNUSED
 #endif
-BTF_ID(func, bpf_stream_vprintk)
-BTF_ID(func, bpf_stream_print_stack)
 
 static bool is_bpf_cast_to_kern_ctx_kfunc(const struct bpf_call_arg_meta *meta)
 {
-- 
2.53.0

[PATCH bpf-next 2/3] bpf: Don't reference arena kfuncs when arena isn't built

[Sasha Levin]

kernel/bpf/Makefile builds arena.o only for CONFIG_MMU && CONFIG_64BIT,
but special_kfunc_list references bpf_arena_alloc_pages() and
bpf_arena_free_pages() unconditionally, so on 32-bit and !MMU kernels
resolve_btfids can't resolve them:

  WARN: resolve_btfids: unresolved symbol bpf_arena_free_pages
  WARN: resolve_btfids: unresolved symbol bpf_arena_alloc_pages

Since commit 201a454df948 ("resolve_btfids: Fix the --fatal_warnings
exit status") these warnings fail the build with CONFIG_WERROR=y, which
breaks i386 builds with CONFIG_DEBUG_INFO_BTF=y:

  Failed to generate BTF for vmlinux
  Try to disable CONFIG_DEBUG_INFO_BTF

Only reference them under the condition arena.o is built with, and use
BTF_ID_UNUSED otherwise to keep the list in sync with enum
special_kfunc_type. An unresolved ID is zero, like BTF_ID_UNUSED, so the
contents of the list don't change.

Fixes: b8467290edab ("bpf: arena: make arena kfuncs any context safe")
Assisted-by: LLM
Signed-off-by: Sasha Levin <sashal@kernel.org>
---
 kernel/bpf/verifier.c | 5 +++++
 1 file changed, 5 insertions(+)

diff --git a/kernel/bpf/verifier.c b/kernel/bpf/verifier.c
index 22f095b9dca2d..12229713a4528 100644
--- a/kernel/bpf/verifier.c
+++ b/kernel/bpf/verifier.c
@@ -13639,8 +13639,13 @@ BTF_ID(func, bpf_task_work_schedule_signal)
 BTF_ID(func, bpf_task_work_schedule_resume)
 BTF_ID(func, bpf_call_rcu)
 BTF_ID(func, bpf_call_rcu_tasks_trace)
+#if defined(CONFIG_MMU) && defined(CONFIG_64BIT)
 BTF_ID(func, bpf_arena_alloc_pages)
 BTF_ID(func, bpf_arena_free_pages)
+#else
+BTF_ID_UNUSED
+BTF_ID_UNUSED
+#endif
 #ifdef CONFIG_BPF_EVENTS
 BTF_ID(func, bpf_session_is_return)
 #else
-- 
2.53.0

[PATCH bpf-next 3/3] bpf: Fix ksock build with BPF_LSM=y and SECURITY_NETWORK=n

[Sasha Levin]

bpf_ksock.c references bpf_lsm_socket_sendmsg() whenever
CONFIG_BPF_LSM=y, but the socket LSM hooks, and with them the BPF LSM
socket_sendmsg hook, only exist with CONFIG_SECURITY_NETWORK=y. Without
it resolve_btfids warns:

  WARN: resolve_btfids: unresolved symbol bpf_lsm_socket_sendmsg

and since commit 201a454df948 ("resolve_btfids: Fix the --fatal_warnings
exit status") that fails the build with CONFIG_WERROR=y.

Only reference the hook with CONFIG_SECURITY_NETWORK=y, and use
BTF_ID_UNUSED otherwise. The ID stays zero, as it was when unresolved,
so bpf_ksock_kfunc_filter() keeps allowing LSM programs: none can be
attached to socket_sendmsg without CONFIG_SECURITY_NETWORK.

Fixes: 7ae4eb14c5f9 ("bpf: Add ksock kfuncs")
Assisted-by: LLM
Signed-off-by: Sasha Levin <sashal@kernel.org>
---
 net/core/bpf_ksock.c | 7 ++++++-
 1 file changed, 6 insertions(+), 1 deletion(-)

diff --git a/net/core/bpf_ksock.c b/net/core/bpf_ksock.c
index 7bf796193ab61..48a2e2327acef 100644
--- a/net/core/bpf_ksock.c
+++ b/net/core/bpf_ksock.c
@@ -258,7 +258,12 @@ BTF_ID_FLAGS(func, bpf_ksock_send, KF_SLEEPABLE)
 BTF_KFUNCS_END(ksock_kfunc_btf_ids)
 
 #ifdef CONFIG_BPF_LSM
-BTF_ID_LIST_SINGLE(bpf_lsm_socket_sendmsg_id, func, bpf_lsm_socket_sendmsg)
+BTF_ID_LIST(bpf_lsm_socket_sendmsg_id)
+#ifdef CONFIG_SECURITY_NETWORK
+BTF_ID(func, bpf_lsm_socket_sendmsg)
+#else
+BTF_ID_UNUSED
+#endif
 #endif
 
 static int bpf_ksock_kfunc_filter(const struct bpf_prog *prog, u32 kfunc_id)
-- 
2.53.0