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Commit b4da3340 authored by Masami Hiramatsu's avatar Masami Hiramatsu Committed by Alexei Starovoitov
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tracing/kprobe: bpf: Check error injectable event is on function entry 



Check whether error injectable event is on function entry or not.
Currently it checks the event is ftrace-based kprobes or not,
but that is wrong. It should check if the event is on the entry
of target function. Since error injection will override a function
to just return with modified return value, that operation must
be done before the target function starts making stackframe.

As a side effect, bpf error injection is no need to depend on
function-tracer. It can work with sw-breakpoint based kprobe
events too.

Signed-off-by: default avatarMasami Hiramatsu <mhiramat@kernel.org>
Reviewed-by: default avatarJosef Bacik <jbacik@fb.com>
Signed-off-by: default avatarAlexei Starovoitov <ast@kernel.org>
parent daaf24c6

arch/x86/include/asm/kprobes.h

+1 −3
Original line number Diff line number Diff line
@@ -67,9 +67,7 @@ extern const int kretprobe_blacklist_size; 
void arch_remove_kprobe(struct kprobe *p);

asmlinkage void kretprobe_trampoline(void);



#ifdef CONFIG_KPROBES_ON_FTRACE

extern void arch_ftrace_kprobe_override_function(struct pt_regs *regs);

#endif

extern void arch_kprobe_override_function(struct pt_regs *regs);



/* Architecture specific copy of original instruction*/

struct arch_specific_insn {

arch/x86/kernel/kprobes/core.c

+14 −0
Original line number Diff line number Diff line
@@ -1183,3 +1183,17 @@ int arch_trampoline_kprobe(struct kprobe *p) 
{

	return 0;

}



asmlinkage void override_func(void);

asm(

	".type override_func, @function\n"

	"override_func:\n"

	"	ret\n"

	".size override_func, .-override_func\n"

);



void arch_kprobe_override_function(struct pt_regs *regs)

{

	regs->ip = (unsigned long)&override_func;

}

NOKPROBE_SYMBOL(arch_kprobe_override_function);

arch/x86/kernel/kprobes/ftrace.c

+0 −14
Original line number Diff line number Diff line
@@ -97,17 +97,3 @@ int arch_prepare_kprobe_ftrace(struct kprobe *p) 
	p->ainsn.boostable = false;

	return 0;

}
 


asmlinkage void override_func(void);

asm(

	".type override_func, @function\n"

	"override_func:\n"

	"	ret\n"

	".size override_func, .-override_func\n"

);



void arch_ftrace_kprobe_override_function(struct pt_regs *regs)

{

	regs->ip = (unsigned long)&override_func;

}

NOKPROBE_SYMBOL(arch_ftrace_kprobe_override_function);

kernel/trace/Kconfig

+0 −2
Original line number Diff line number Diff line
@@ -533,9 +533,7 @@ config FUNCTION_PROFILER 
config BPF_KPROBE_OVERRIDE

	bool "Enable BPF programs to override a kprobed function"

	depends on BPF_EVENTS

	depends on KPROBES_ON_FTRACE

	depends on HAVE_KPROBE_OVERRIDE

	depends on DYNAMIC_FTRACE_WITH_REGS

	default n

	help

	 Allows BPF to override the execution of a probed function and

kernel/trace/bpf_trace.c

+4 −4
Original line number Diff line number Diff line
@@ -85,7 +85,7 @@ BPF_CALL_2(bpf_override_return, struct pt_regs *, regs, unsigned long, rc) 
{

	__this_cpu_write(bpf_kprobe_override, 1);

	regs_set_return_value(regs, rc);

	arch_ftrace_kprobe_override_function(regs);

	arch_kprobe_override_function(regs);

	return 0;

}
@@ -800,11 +800,11 @@ int perf_event_attach_bpf_prog(struct perf_event *event, 
	int ret = -EEXIST;



	/*

	 * Kprobe override only works for ftrace based kprobes, and only if they

	 * are on the opt-in list.

	 * Kprobe override only works if they are on the function entry,

	 * and only if they are on the opt-in list.

	 */

	if (prog->kprobe_override &&

	    (!trace_kprobe_ftrace(event->tp_event) ||

	    (!trace_kprobe_on_func_entry(event->tp_event) ||

	     !trace_kprobe_error_injectable(event->tp_event)))

		return -EINVAL;