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libbpf: Clarify kernel type use with USER variants of CORE reading macros

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Add comments clarifying that USER variants of CO-RE reading macro are still
only going to work with kernel types, defined in kernel or kernel module BTF.
This should help preventing invalid use of those macro to read user-defined
types (which doesn't work with CO-RE).

Signed-off-by: Andrii Nakryiko <andrii@kernel.org>
Signed-off-by: Alexei Starovoitov <ast@kernel.org>
Link: https://lore.kernel.org/bpf/20210108194408.3468860-1-andrii@kernel.org
This commit is contained in:
Andrii Nakryiko 2021-01-08 11:44:08 -08:00 committed by Alexei Starovoitov
parent 9a8120a8d7
commit e22d7f05e4
1 changed files with 39 additions and 6 deletions
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45
tools/lib/bpf/bpf_core_read.h
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@ -197,6 +197,7 @@ enum bpf_enum_value_kind {
#define bpf_core_read(dst, sz, src) \
bpf_probe_read_kernel(dst, sz, (const void *)__builtin_preserve_access_index(src))
/* NOTE: see comments for BPF_CORE_READ_USER() about the proper types use. */
#define bpf_core_read_user(dst, sz, src) \
bpf_probe_read_user(dst, sz, (const void *)__builtin_preserve_access_index(src))
/*
@ -207,6 +208,7 @@ enum bpf_enum_value_kind {
#define bpf_core_read_str(dst, sz, src) \
bpf_probe_read_kernel_str(dst, sz, (const void *)__builtin_preserve_access_index(src))
/* NOTE: see comments for BPF_CORE_READ_USER() about the proper types use. */
#define bpf_core_read_user_str(dst, sz, src) \
bpf_probe_read_user_str(dst, sz, (const void *)__builtin_preserve_access_index(src))
@ -302,7 +304,11 @@ enum bpf_enum_value_kind {
dst, (src), a, ##__VA_ARGS__) \
})
/* Variant of BPF_CORE_READ_INTO() for reading from user-space memory */
/*
* Variant of BPF_CORE_READ_INTO() for reading from user-space memory.
*
* NOTE: see comments for BPF_CORE_READ_USER() about the proper types use.
*/
#define BPF_CORE_READ_USER_INTO(dst, src, a, ...) ({ \
___core_read(bpf_core_read_user, bpf_core_read_user, \
dst, (src), a, ##__VA_ARGS__) \
@ -314,7 +320,11 @@ enum bpf_enum_value_kind {
dst, (src), a, ##__VA_ARGS__) \
})
/* Non-CO-RE variant of BPF_CORE_READ_USER_INTO() */
/* Non-CO-RE variant of BPF_CORE_READ_USER_INTO().
*
* As no CO-RE relocations are emitted, source types can be arbitrary and are
* not restricted to kernel types only.
*/
#define BPF_PROBE_READ_USER_INTO(dst, src, a, ...) ({ \
___core_read(bpf_probe_read_user, bpf_probe_read_user, \
dst, (src), a, ##__VA_ARGS__) \
@ -330,7 +340,11 @@ enum bpf_enum_value_kind {
dst, (src), a, ##__VA_ARGS__) \
})
/* Variant of BPF_CORE_READ_STR_INTO() for reading from user-space memory */
/*
* Variant of BPF_CORE_READ_STR_INTO() for reading from user-space memory.
*
* NOTE: see comments for BPF_CORE_READ_USER() about the proper types use.
*/
#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__) \
@ -342,7 +356,12 @@ enum bpf_enum_value_kind {
dst, (src), a, ##__VA_ARGS__) \
})
/* Non-CO-RE variant of BPF_CORE_READ_USER_STR_INTO() */
/*
* Non-CO-RE variant of BPF_CORE_READ_USER_STR_INTO().
*
* As no CO-RE relocations are emitted, source types can be arbitrary and are
* not restricted to kernel types only.
*/
#define BPF_PROBE_READ_USER_STR_INTO(dst, src, a, ...) ({ \
___core_read(bpf_probe_read_user_str, bpf_probe_read_user, \
dst, (src), a, ##__VA_ARGS__) \
@ -378,7 +397,16 @@ enum bpf_enum_value_kind {
__r; \
})
/* Variant of BPF_CORE_READ() for reading from user-space memory */
/*
* Variant of BPF_CORE_READ() for reading from user-space memory.
*
* NOTE: all the source types involved are still *kernel types* and need to
* exist in kernel (or kernel module) BTF, otherwise CO-RE relocation will
* fail. Custom user types are not relocatable with CO-RE.
* The typical situation in which BPF_CORE_READ_USER() might be used is to
* read kernel UAPI types from the user-space memory passed in as a syscall
* input argument.
*/
#define BPF_CORE_READ_USER(src, a, ...) ({ \
___type((src), a, ##__VA_ARGS__) __r; \
BPF_CORE_READ_USER_INTO(&__r, (src), a, ##__VA_ARGS__); \
@ -392,7 +420,12 @@ enum bpf_enum_value_kind {
__r; \
})
/* Non-CO-RE variant of BPF_CORE_READ_USER() */
/*
* Non-CO-RE variant of BPF_CORE_READ_USER().
*
* As no CO-RE relocations are emitted, source types can be arbitrary and are
* not restricted to kernel types only.
*/
#define BPF_PROBE_READ_USER(src, a, ...) ({ \
___type((src), a, ##__VA_ARGS__) __r; \
BPF_PROBE_READ_USER_INTO(&__r, (src), a, ##__VA_ARGS__); \