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

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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>
This commit is contained in:
Andrii Nakryiko 2020-12-18 15:56:12 -08:00 committed by Alexei Starovoitov
parent 833d22f2f9
commit 792001f4f7
1 changed files with 58 additions and 38 deletions
repo.diff.show_diff_stats Download patch file Download diff file Expand all files Collapse all files

96
tools/lib/bpf/bpf_core_read.h
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@ -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 ___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, dst, src, a) \
#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