bpf: add BPF_CALL_x macros for declaring helpers

This work adds BPF_CALL_<n>() macros and converts all the eBPF helper functions
to use them, in a similar fashion like we do with SYSCALL_DEFINE<n>() macros
that are used today. Motivation for this is to hide all the register handling
and all necessary casts from the user, so that it is done automatically in the
background when adding a BPF_CALL_<n>() call.

This makes current helpers easier to review, eases to write future helpers,
avoids getting the casting mess wrong, and allows for extending all helpers at
once (f.e. build time checks, etc). It also helps detecting more easily in
code reviews that unused registers are not instrumented in the code by accident,
breaking compatibility with existing programs.

BPF_CALL_<n>() internals are quite similar to SYSCALL_DEFINE<n>() ones with some
fundamental differences, for example, for generating the actual helper function
that carries all u64 regs, we need to fill unused regs, so that we always end up
with 5 u64 regs as an argument.

I reviewed several 0-5 generated BPF_CALL_<n>() variants of the .i results and
they look all as expected. No sparse issue spotted. We let this also sit for a
few days with Fengguang's kbuild test robot, and there were no issues seen. On
s390, it barked on the "uses dynamic stack allocation" notice, which is an old
one from bpf_perf_event_output{,_tp}() reappearing here due to the conversion
to the call wrapper, just telling that the perf raw record/frag sits on stack
(gcc with s390's -mwarn-dynamicstack), but that's all. Did various runtime tests
and they were fine as well. All eBPF helpers are now converted to use these
macros, getting rid of a good chunk of all the raw castings.

Signed-off-by: Daniel Borkmann <daniel@iogearbox.net>
Acked-by: Alexei Starovoitov <ast@kernel.org>
Signed-off-by: David S. Miller <davem@davemloft.net>

1 files changed, 50 insertions, 0 deletions

diff --git a/include/linux/filter.h b/include/linux/filter.h
index 7fabad8dc3fc..1f09c521adfe 100644
--- a/include/linux/filter.h
+++ b/include/linux/filter.h
@@ -328,6 +328,56 @@ struct bpf_prog_aux;
 		__size;						\
 	})
 
+#define __BPF_MAP_0(m, v, ...) v
+#define __BPF_MAP_1(m, v, t, a, ...) m(t, a)
+#define __BPF_MAP_2(m, v, t, a, ...) m(t, a), __BPF_MAP_1(m, v, __VA_ARGS__)
+#define __BPF_MAP_3(m, v, t, a, ...) m(t, a), __BPF_MAP_2(m, v, __VA_ARGS__)
+#define __BPF_MAP_4(m, v, t, a, ...) m(t, a), __BPF_MAP_3(m, v, __VA_ARGS__)
+#define __BPF_MAP_5(m, v, t, a, ...) m(t, a), __BPF_MAP_4(m, v, __VA_ARGS__)
+
+#define __BPF_REG_0(...) __BPF_PAD(5)
+#define __BPF_REG_1(...) __BPF_MAP(1, __VA_ARGS__), __BPF_PAD(4)
+#define __BPF_REG_2(...) __BPF_MAP(2, __VA_ARGS__), __BPF_PAD(3)
+#define __BPF_REG_3(...) __BPF_MAP(3, __VA_ARGS__), __BPF_PAD(2)
+#define __BPF_REG_4(...) __BPF_MAP(4, __VA_ARGS__), __BPF_PAD(1)
+#define __BPF_REG_5(...) __BPF_MAP(5, __VA_ARGS__)
+
+#define __BPF_MAP(n, ...) __BPF_MAP_##n(__VA_ARGS__)
+#define __BPF_REG(n, ...) __BPF_REG_##n(__VA_ARGS__)
+
+#define __BPF_CAST(t, a)						       \
+	(__force t)							       \
+	(__force							       \
+	 typeof(__builtin_choose_expr(sizeof(t) == sizeof(unsigned long),      \
+				      (unsigned long)0, (t)0))) a
+#define __BPF_V void
+#define __BPF_N
+
+#define __BPF_DECL_ARGS(t, a) t   a
+#define __BPF_DECL_REGS(t, a) u64 a
+
+#define __BPF_PAD(n)							       \
+	__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, ...)					       \
+	static __always_inline						       \
+	u64 ____##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 ____##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__)
+
 #ifdef CONFIG_COMPAT
 /* A struct sock_filter is architecture independent. */
 struct compat_sock_fprog {