Commit e22d7f05 authored by Andrii Nakryiko's avatar Andrii Nakryiko Committed by Alexei Starovoitov
Browse files

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



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: default avatarAndrii Nakryiko <andrii@kernel.org>
Signed-off-by: default avatarAlexei Starovoitov <ast@kernel.org>
Link: https://lore.kernel.org/bpf/20210108194408.3468860-1-andrii@kernel.org
parent 9a8120a8

tools/lib/bpf/bpf_core_read.h

+39 −6
Original line number Diff line number Diff line
@@ -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__);	    \