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.org
Signed-off-by: Alexei Starovoitov <ast@kernel.org>

diff --git a/tools/lib/bpf/bpf_core_read.h b/tools/lib/bpf/bpf_core_read.h
index bbcefb3..db0c735 100644 (file)
--- a/tools/lib/bpf/bpf_core_read.h
+++ b/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, ...)                                         \
-       ({                                                                  \
-               ___type((src), a, ##__VA_ARGS__) __r;                       \
-               BPF_CORE_READ_INTO(&__r, (src), a, ##__VA_ARGS__);          \
-               __r;                                                        \
-       })
+#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