[PATCH bpf-next 1/2] bpf: Mark bpf_spin_{lock,unlock}() helpers with notrace correctly

[Yonghong Song <yonghong.song@linux.dev>]

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-iFuMZgW06qp0KHWtpvoXxf1OAQ@mail.gmail.com/
  [2] https://lore.kernel.org/bpf/CAE5sdEg6yUc_Jz50AnUXEEUh6O73yQ1Z6NV2srJnef0ZrQkZew@mail.gmail.com/

Fixes: d83525ca62cf ("bpf: introduce bpf_spin_lock")
Cc: Siddharth Chintamaneni <sidchintamaneni@gmail.com>
Signed-off-by: Yonghong Song <yonghong.song@linux.dev>
---
 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 fee070b9826e..36cc29a2934c 100644
--- a/include/linux/filter.h
+++ b/include/linux/filter.h
@@ -547,24 +547,27 @@ 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 4db1c658254c..87136e27a99a 100644
--- a/kernel/bpf/helpers.c
+++ b/kernel/bpf/helpers.c
@@ -334,7 +334,7 @@ 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;
@@ -357,7 +357,7 @@ 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;
-- 
2.34.1