From: Yonghong Song yonghong.song@linux.dev
[ Upstream commit 178c54666f9c4d2f49f2ea661d0c11b52f0ed190 ]
Currently tracing is supposed not to allow for bpf_spin_{lock,unlock}() helper calls. This is to prevent deadlock for the following cases: - there is a prog (prog-A) calling bpf_spin_{lock,unlock}(). - there is a tracing program (prog-B), e.g., fentry, attached to bpf_spin_lock() and/or bpf_spin_unlock(). - prog-B calls bpf_spin_{lock,unlock}(). For such a case, when prog-A calls bpf_spin_{lock,unlock}(), a deadlock will happen.
The related source codes are below in kernel/bpf/helpers.c: notrace BPF_CALL_1(bpf_spin_lock, struct bpf_spin_lock *, lock) notrace BPF_CALL_1(bpf_spin_unlock, struct bpf_spin_lock *, lock) notrace is supposed to prevent fentry prog from attaching to bpf_spin_{lock,unlock}().
But actually this is not the case and fentry prog can successfully attached to bpf_spin_lock(). Siddharth Chintamaneni reported the issue in [1]. The following is the macro definition for above BPF_CALL_1: #define BPF_CALL_x(x, name, ...) \ static __always_inline \ u64 ____##name(__BPF_MAP(x, __BPF_DECL_ARGS, __BPF_V, __VA_ARGS__)); \ typedef u64 (*btf_##name)(__BPF_MAP(x, __BPF_DECL_ARGS, __BPF_V, __VA_ARGS__)); \ u64 name(__BPF_REG(x, __BPF_DECL_REGS, __BPF_N, __VA_ARGS__)); \ u64 name(__BPF_REG(x, __BPF_DECL_REGS, __BPF_N, __VA_ARGS__)) \ { \ return ((btf_##name)____##name)(__BPF_MAP(x,__BPF_CAST,__BPF_N,__VA_ARGS__));\ } \ static __always_inline \ u64 ____##name(__BPF_MAP(x, __BPF_DECL_ARGS, __BPF_V, __VA_ARGS__))
#define BPF_CALL_1(name, ...) BPF_CALL_x(1, name, __VA_ARGS__)
The notrace attribute is actually applied to the static always_inline function ____bpf_spin_{lock,unlock}(). The actual callback function bpf_spin_{lock,unlock}() is not marked with notrace, hence allowing fentry prog to attach to two helpers, and this may cause the above mentioned deadlock. Siddharth Chintamaneni actually has a reproducer in [2].
To fix the issue, a new macro NOTRACE_BPF_CALL_1 is introduced which will add notrace attribute to the original function instead of the hidden always_inline function and this fixed the problem.
[1] https://lore.kernel.org/bpf/CAE5sdEigPnoGrzN8WU7Tx-h-iFuMZgW06qp0KHWtpvoXxf1... [2] https://lore.kernel.org/bpf/CAE5sdEg6yUc_Jz50AnUXEEUh6O73yQ1Z6NV2srJnef0ZrQk...
Fixes: d83525ca62cf ("bpf: introduce bpf_spin_lock") Signed-off-by: Yonghong Song yonghong.song@linux.dev Signed-off-by: Andrii Nakryiko andrii@kernel.org Acked-by: Jiri Olsa jolsa@kernel.org Link: https://lore.kernel.org/bpf/20240207070102.335167-1-yonghong.song@linux.dev Signed-off-by: Sasha Levin sashal@kernel.org --- include/linux/filter.h | 21 ++++++++++++--------- kernel/bpf/helpers.c | 4 ++-- 2 files changed, 14 insertions(+), 11 deletions(-)
diff --git a/include/linux/filter.h b/include/linux/filter.h index 11407e9e606db..0bec300b2e516 100644 --- a/include/linux/filter.h +++ b/include/linux/filter.h @@ -476,24 +476,27 @@ static inline bool insn_is_zext(const struct bpf_insn *insn) __BPF_MAP(n, __BPF_DECL_ARGS, __BPF_N, u64, __ur_1, u64, __ur_2, \ u64, __ur_3, u64, __ur_4, u64, __ur_5)
-#define BPF_CALL_x(x, name, ...) \ +#define BPF_CALL_x(x, attr, name, ...) \ static __always_inline \ u64 ____##name(__BPF_MAP(x, __BPF_DECL_ARGS, __BPF_V, __VA_ARGS__)); \ typedef u64 (*btf_##name)(__BPF_MAP(x, __BPF_DECL_ARGS, __BPF_V, __VA_ARGS__)); \ - u64 name(__BPF_REG(x, __BPF_DECL_REGS, __BPF_N, __VA_ARGS__)); \ - u64 name(__BPF_REG(x, __BPF_DECL_REGS, __BPF_N, __VA_ARGS__)) \ + attr u64 name(__BPF_REG(x, __BPF_DECL_REGS, __BPF_N, __VA_ARGS__)); \ + attr u64 name(__BPF_REG(x, __BPF_DECL_REGS, __BPF_N, __VA_ARGS__)) \ { \ return ((btf_##name)____##name)(__BPF_MAP(x,__BPF_CAST,__BPF_N,__VA_ARGS__));\ } \ static __always_inline \ u64 ____##name(__BPF_MAP(x, __BPF_DECL_ARGS, __BPF_V, __VA_ARGS__))
-#define BPF_CALL_0(name, ...) BPF_CALL_x(0, name, __VA_ARGS__) -#define BPF_CALL_1(name, ...) BPF_CALL_x(1, name, __VA_ARGS__) -#define BPF_CALL_2(name, ...) BPF_CALL_x(2, name, __VA_ARGS__) -#define BPF_CALL_3(name, ...) BPF_CALL_x(3, name, __VA_ARGS__) -#define BPF_CALL_4(name, ...) BPF_CALL_x(4, name, __VA_ARGS__) -#define BPF_CALL_5(name, ...) BPF_CALL_x(5, name, __VA_ARGS__) +#define __NOATTR +#define BPF_CALL_0(name, ...) BPF_CALL_x(0, __NOATTR, name, __VA_ARGS__) +#define BPF_CALL_1(name, ...) BPF_CALL_x(1, __NOATTR, name, __VA_ARGS__) +#define BPF_CALL_2(name, ...) BPF_CALL_x(2, __NOATTR, name, __VA_ARGS__) +#define BPF_CALL_3(name, ...) BPF_CALL_x(3, __NOATTR, name, __VA_ARGS__) +#define BPF_CALL_4(name, ...) BPF_CALL_x(4, __NOATTR, name, __VA_ARGS__) +#define BPF_CALL_5(name, ...) BPF_CALL_x(5, __NOATTR, name, __VA_ARGS__) + +#define NOTRACE_BPF_CALL_1(name, ...) BPF_CALL_x(1, notrace, name, __VA_ARGS__)
#define bpf_ctx_range(TYPE, MEMBER) \ offsetof(TYPE, MEMBER) ... offsetofend(TYPE, MEMBER) - 1 diff --git a/kernel/bpf/helpers.c b/kernel/bpf/helpers.c index 4ba3dc621a345..9bfb4685d0684 100644 --- a/kernel/bpf/helpers.c +++ b/kernel/bpf/helpers.c @@ -271,7 +271,7 @@ static inline void __bpf_spin_lock_irqsave(struct bpf_spin_lock *lock) __this_cpu_write(irqsave_flags, flags); }
-notrace BPF_CALL_1(bpf_spin_lock, struct bpf_spin_lock *, lock) +NOTRACE_BPF_CALL_1(bpf_spin_lock, struct bpf_spin_lock *, lock) { __bpf_spin_lock_irqsave(lock); return 0; @@ -293,7 +293,7 @@ static inline void __bpf_spin_unlock_irqrestore(struct bpf_spin_lock *lock) local_irq_restore(flags); }
-notrace BPF_CALL_1(bpf_spin_unlock, struct bpf_spin_lock *, lock) +NOTRACE_BPF_CALL_1(bpf_spin_unlock, struct bpf_spin_lock *, lock) { __bpf_spin_unlock_irqrestore(lock); return 0;