Re: [PATCH bpf-next v3 1/5] tracing/kprobe: bpf: Check error injectable event is on function entry

[Josef Bacik]

On Wed, Jan 10, 2018 at 07:17:06PM +0900, Masami Hiramatsu wrote:
> 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: Masami Hiramatsu 

Reviewed-by: Josef Bacik 

Thanks,

Josef

[PATCH bpf-next v3 1/5] tracing/kprobe: bpf: Check error injectable event is on function entry

[Masami Hiramatsu]

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: Masami Hiramatsu 
---
  Changes in v3:
   - Move arch_ftrace_kprobe_override_function() to
 core.c because it is no longer depending on ftrace.
   - Fix a bug to skip passing kprobes target name to
 kprobe_on_func_entry(). Passing both @addr and @symbol
 to that function will result in failure.
---
 arch/x86/include/asm/kprobes.h   |4 +---
 arch/x86/kernel/kprobes/core.c   |   14 ++
 arch/x86/kernel/kprobes/ftrace.c |   14 --
 kernel/trace/Kconfig |2 --
 kernel/trace/bpf_trace.c |8 
 kernel/trace/trace_kprobe.c  |9 ++---
 kernel/trace/trace_probe.h   |   12 ++--
 7 files changed, 31 insertions(+), 32 deletions(-)

diff --git a/arch/x86/include/asm/kprobes.h b/arch/x86/include/asm/kprobes.h
index 36abb23a7a35..367d99cff426 100644
--- a/arch/x86/include/asm/kprobes.h
+++ b/arch/x86/include/asm/kprobes.h
@@ -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 {
diff --git a/arch/x86/kernel/kprobes/core.c b/arch/x86/kernel/kprobes/core.c
index bd36f3c33cd0..b02a377d5905 100644
--- a/arch/x86/kernel/kprobes/core.c
+++ b/arch/x86/kernel/kprobes/core.c
@@ -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)_func;
+}
+NOKPROBE_SYMBOL(arch_kprobe_override_function);
diff --git a/arch/x86/kernel/kprobes/ftrace.c b/arch/x86/kernel/kprobes/ftrace.c
index 1ea748d682fd..8dc0161cec8f 100644
--- a/arch/x86/kernel/kprobes/ftrace.c
+++ b/arch/x86/kernel/kprobes/ftrace.c
@@ -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)_func;
-}
-NOKPROBE_SYMBOL(arch_ftrace_kprobe_override_function);
diff --git a/kernel/trace/Kconfig b/kernel/trace/Kconfig
index ae3a2d519e50..6400e1bf97c5 100644
--- a/kernel/trace/Kconfig
+++ b/kernel/trace/Kconfig
@@ -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
diff --git a/kernel/trace/bpf_trace.c b/kernel/trace/bpf_trace.c
index f6d2327ecb59..1966ad3bf3e0 100644
--- a/kernel/trace/bpf_trace.c
+++ b/kernel/trace/bpf_trace.c
@@ -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;
 
diff --git a/kernel/trace/trace_kprobe.c b/kernel/trace/trace_kprobe.c
index 91f4b57dab82..3c8deb977a8b 100644
--- a/kernel/trace/trace_kprobe.c
+++