The dispatcher function is attached/detached to trampoline by
dispatcher update function. At the same time it's available as
ftrace attachable function.
After discussion [1] the proposed solution is to use compiler
attributes to alter bpf_dispatcher_##name##_func function:
- remove it from being instrumented with __no_instrument_function__
attribute, so ftrace has no track of it
- but still generate 5 nop instructions with patchable_function_entry(5)
attribute, which are expected by bpf_arch_text_poke used by
dispatcher update function
Enabling HAVE_DYNAMIC_FTRACE_NO_PATCHABLE option for x86, so
__patchable_function_entries functions are not part of ftrace/mcount
locations.
Adding attributes to bpf_dispatcher_XXX function on x86_64 so it's
kept out of ftrace locations and has 5 byte nop generated at entry.
These attributes need to be arch specific as pointed out by Ilya
Leoshkevic in here [2].
The dispatcher image is generated only for x86_64 arch, so the
code can stay as is for other archs.
[1] https://lore.kernel.org/bpf/
20220722110811.124515-1-jolsa@kernel.org/
[2] https://lore.kernel.org/bpf/
969a14281a7791c334d476825863ee449964dd0c.camel@linux.ibm.com/
Suggested-by: Peter Zijlstra (Intel) <peterz@infradead.org>
Signed-off-by: Jiri Olsa <jolsa@kernel.org>
Signed-off-by: Daniel Borkmann <daniel@iogearbox.net>
Acked-by: Peter Zijlstra (Intel) <peterz@infradead.org>
Link: https://lore.kernel.org/bpf/20220903131154.420467-3-jolsa@kernel.org
select PROC_PID_ARCH_STATUS if PROC_FS
select HAVE_ARCH_NODE_DEV_GROUP if X86_SGX
imply IMA_SECURE_AND_OR_TRUSTED_BOOT if EFI
+ select HAVE_DYNAMIC_FTRACE_NO_PATCHABLE
config INSTRUCTION_DECODER
def_bool y
}, \
}
+#ifdef CONFIG_X86_64
+#define BPF_DISPATCHER_ATTRIBUTES __attribute__((patchable_function_entry(5)))
+#else
+#define BPF_DISPATCHER_ATTRIBUTES
+#endif
+
#define DEFINE_BPF_DISPATCHER(name) \
+ notrace BPF_DISPATCHER_ATTRIBUTES \
noinline __nocfi unsigned int bpf_dispatcher_##name##_func( \
const void *ctx, \
const struct bpf_insn *insnsi, \