libbpf: Add user-space variants of BPF_CORE_READ() family of macros

Add BPF_CORE_READ_USER(), BPF_CORE_READ_USER_STR() and their _INTO()
variations to allow reading CO-RE-relocatable kernel data structures from the
user-space. One of such cases is reading input arguments of syscalls, while
reaping the benefits of CO-RE relocations w.r.t. handling 32/64 bit
conversions and handling missing/new fields in UAPI data structs.
Suggested-by: Gilad Reti <gilad.reti@gmail.com>
Signed-off-by: Andrii Nakryiko <andrii@kernel.org>
Signed-off-by: Daniel Borkmann <daniel@iogearbox.net>
Link: https://lore.kernel.org/bpf/20201218235614.2284956-2-andrii@kernel.orgSigned-off-by: Alexei Starovoitov <ast@kernel.org>

tools/lib/bpf/bpf_core_read.h

@@ -195,17 +195,20 @@ enum bpf_enum_value_kind {
  * (local) BTF, used to record relocation.
  */
 #define bpf_core_read(dst, sz, src)					    \
-	bpf_probe_read_kernel(dst, sz,					    \
-			      (const void *)__builtin_preserve_access_index(src))
+	bpf_probe_read_kernel(dst, sz, (const void *)__builtin_preserve_access_index(src))
 
+#define bpf_core_read_user(dst, sz, src)				    \
+	bpf_probe_read_user(dst, sz, (const void *)__builtin_preserve_access_index(src))
 /*
  * bpf_core_read_str() is a thin wrapper around bpf_probe_read_str()
  * additionally emitting BPF CO-RE field relocation for specified source
  * argument.
  */
 #define bpf_core_read_str(dst, sz, src)					    \
-	bpf_probe_read_kernel_str(dst, sz,				    \
-				  (const void *)__builtin_preserve_access_index(src))
+	bpf_probe_read_kernel_str(dst, sz, (const void *)__builtin_preserve_access_index(src))
+
+#define bpf_core_read_user_str(dst, sz, src)				    \
+	bpf_probe_read_user_str(dst, sz, (const void *)__builtin_preserve_access_index(src))
 
 #define ___concat(a, b) a ## b
 #define ___apply(fn, n) ___concat(fn, n)
@@ -264,30 +267,29 @@ enum bpf_enum_value_kind {
 	read_fn((void *)(dst), sizeof(*(dst)), &((src_type)(src))->accessor)
 
 /* "recursively" read a sequence of inner pointers using local __t var */
-#define ___rd_first(src, a) ___read(bpf_core_read, &__t, ___type(src), src, a);
-#define ___rd_last(...)							    \
-	___read(bpf_core_read, &__t,					    \
-		___type(___nolast(__VA_ARGS__)), __t, ___last(__VA_ARGS__));
-#define ___rd_p1(...) const void *__t; ___rd_first(__VA_ARGS__)
-#define ___rd_p2(...) ___rd_p1(___nolast(__VA_ARGS__)) ___rd_last(__VA_ARGS__)
-#define ___rd_p3(...) ___rd_p2(___nolast(__VA_ARGS__)) ___rd_last(__VA_ARGS__)
-#define ___rd_p4(...) ___rd_p3(___nolast(__VA_ARGS__)) ___rd_last(__VA_ARGS__)
-#define ___rd_p5(...) ___rd_p4(___nolast(__VA_ARGS__)) ___rd_last(__VA_ARGS__)
-#define ___rd_p6(...) ___rd_p5(___nolast(__VA_ARGS__)) ___rd_last(__VA_ARGS__)
-#define ___rd_p7(...) ___rd_p6(___nolast(__VA_ARGS__)) ___rd_last(__VA_ARGS__)
-#define ___rd_p8(...) ___rd_p7(___nolast(__VA_ARGS__)) ___rd_last(__VA_ARGS__)
-#define ___rd_p9(...) ___rd_p8(___nolast(__VA_ARGS__)) ___rd_last(__VA_ARGS__)
-#define ___read_ptrs(src, ...)						    \
-	___apply(___rd_p, ___narg(__VA_ARGS__))(src, __VA_ARGS__)
-
-#define ___core_read0(fn, dst, src, a)					    \
+#define ___rd_first(fn, src, a) ___read(fn, &__t, ___type(src), src, a);
+#define ___rd_last(fn, ...)						    \
+	___read(fn, &__t, ___type(___nolast(__VA_ARGS__)), __t, ___last(__VA_ARGS__));
+#define ___rd_p1(fn, ...) const void *__t; ___rd_first(fn, __VA_ARGS__)
+#define ___rd_p2(fn, ...) ___rd_p1(fn, ___nolast(__VA_ARGS__)) ___rd_last(fn, __VA_ARGS__)
+#define ___rd_p3(fn, ...) ___rd_p2(fn, ___nolast(__VA_ARGS__)) ___rd_last(fn, __VA_ARGS__)
+#define ___rd_p4(fn, ...) ___rd_p3(fn, ___nolast(__VA_ARGS__)) ___rd_last(fn, __VA_ARGS__)
+#define ___rd_p5(fn, ...) ___rd_p4(fn, ___nolast(__VA_ARGS__)) ___rd_last(fn, __VA_ARGS__)
+#define ___rd_p6(fn, ...) ___rd_p5(fn, ___nolast(__VA_ARGS__)) ___rd_last(fn, __VA_ARGS__)
+#define ___rd_p7(fn, ...) ___rd_p6(fn, ___nolast(__VA_ARGS__)) ___rd_last(fn, __VA_ARGS__)
+#define ___rd_p8(fn, ...) ___rd_p7(fn, ___nolast(__VA_ARGS__)) ___rd_last(fn, __VA_ARGS__)
+#define ___rd_p9(fn, ...) ___rd_p8(fn, ___nolast(__VA_ARGS__)) ___rd_last(fn, __VA_ARGS__)
+#define ___read_ptrs(fn, src, ...)					    \
+	___apply(___rd_p, ___narg(__VA_ARGS__))(fn, src, __VA_ARGS__)
+
+#define ___core_read0(fn, fn_ptr, dst, src, a)				    \
 	___read(fn, dst, ___type(src), src, a);
-#define ___core_readN(fn, dst, src, ...)				    \
-	___read_ptrs(src, ___nolast(__VA_ARGS__))			    \
+#define ___core_readN(fn, fn_ptr, dst, src, ...)			    \
+	___read_ptrs(fn_ptr, src, ___nolast(__VA_ARGS__))		    \
 	___read(fn, dst, ___type(src, ___nolast(__VA_ARGS__)), __t,	    \
 		___last(__VA_ARGS__));
-#define ___core_read(fn, dst, src, a, ...)				    \
-	___apply(___core_read, ___empty(__VA_ARGS__))(fn, dst,		    \
+#define ___core_read(fn, fn_ptr, dst, src, a, ...)			    \
+	___apply(___core_read, ___empty(__VA_ARGS__))(fn, fn_ptr, dst,	    \
 						      src, a, ##__VA_ARGS__)
 
 /*
@@ -295,20 +297,32 @@ enum bpf_enum_value_kind {
  * BPF_CORE_READ(), in which final field is read into user-provided storage.
  * See BPF_CORE_READ() below for more details on general usage.
  */
-#define BPF_CORE_READ_INTO(dst, src, a, ...)				    \
-	({								    \
-		___core_read(bpf_core_read, dst, (src), a, ##__VA_ARGS__)   \
-	})
+#define BPF_CORE_READ_INTO(dst, src, a, ...) ({				    \
+	___core_read(bpf_core_read, bpf_core_read,			    \
+		     dst, (src), a, ##__VA_ARGS__)			    \
+})
+
+/* Variant of BPF_CORE_READ_INTO() for reading from user-space memory */
+#define BPF_CORE_READ_USER_INTO(dst, src, a, ...) ({			    \
+	___core_read(bpf_core_read_user, bpf_core_read_user,		    \
+		     dst, (src), a, ##__VA_ARGS__)			    \
+})
 
 /*
  * BPF_CORE_READ_STR_INTO() does same "pointer chasing" as
  * BPF_CORE_READ() for intermediate pointers, but then executes (and returns
  * corresponding error code) bpf_core_read_str() for final string read.
  */
-#define BPF_CORE_READ_STR_INTO(dst, src, a, ...)			    \
-	({								    \
-		___core_read(bpf_core_read_str, dst, (src), a, ##__VA_ARGS__)\
-	})
+#define BPF_CORE_READ_STR_INTO(dst, src, a, ...) ({			    \
+	___core_read(bpf_core_read_str, bpf_core_read,			    \
+		     dst, (src), a, ##__VA_ARGS__)			    \
+})
+
+/* Variant of BPF_CORE_READ_STR_INTO() for reading from user-space memory */
+#define BPF_CORE_READ_USER_STR_INTO(dst, src, a, ...) ({		    \
+	___core_read(bpf_core_read_user_str, bpf_core_read_user,	    \
+		     dst, (src), a, ##__VA_ARGS__)			    \
+})
 
 /*
  * BPF_CORE_READ() is used to simplify BPF CO-RE relocatable read, especially
@@ -334,12 +348,18 @@ enum bpf_enum_value_kind {
  * N.B. Only up to 9 "field accessors" are supported, which should be more
  * than enough for any practical purpose.
  */
-#define BPF_CORE_READ(src, a, ...)					    \
-	({								    \
+#define BPF_CORE_READ(src, a, ...) ({					    \
 	___type((src), a, ##__VA_ARGS__) __r;				    \
 	BPF_CORE_READ_INTO(&__r, (src), a, ##__VA_ARGS__);		    \
 	__r;								    \
-	})
+})
+
+/* Variant of BPF_CORE_READ() for reading from user-space memory */
+#define BPF_CORE_READ_USER(src, a, ...) ({				    \
+	___type((src), a, ##__VA_ARGS__) __r;				    \
+	BPF_CORE_READ_USER_INTO(&__r, (src), a, ##__VA_ARGS__);		    \
+	__r;								    \
+})
 
 #endif