Re: [PATCH v7 3/5] bpf: add a bpf_override_function helper

[Daniel Borkmann]

On 11/22/2017 10:23 PM, Josef Bacik wrote:
> From: Josef Bacik 
> 
> Error injection is sloppy and very ad-hoc.  BPF could fill this niche
> perfectly with it's kprobe functionality.  We could make sure errors are
> only triggered in specific call chains that we care about with very
> specific situations.  Accomplish this with the bpf_override_funciton
> helper.  This will modify the probe'd callers return value to the
> specified value and set the PC to an override function that simply
> returns, bypassing the originally probed function.  This gives us a nice
> clean way to implement systematic error injection for all of our code
> paths.
> 
> Acked-by: Alexei Starovoitov 
> Acked-by: Ingo Molnar 
> Signed-off-by: Josef Bacik 

Series looks good to me as well; BPF bits:

Acked-by: Daniel Borkmann 
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[PATCH v7 3/5] bpf: add a bpf_override_function helper

[Josef Bacik]

From: Josef Bacik 

Error injection is sloppy and very ad-hoc.  BPF could fill this niche
perfectly with it's kprobe functionality.  We could make sure errors are
only triggered in specific call chains that we care about with very
specific situations.  Accomplish this with the bpf_override_funciton
helper.  This will modify the probe'd callers return value to the
specified value and set the PC to an override function that simply
returns, bypassing the originally probed function.  This gives us a nice
clean way to implement systematic error injection for all of our code
paths.

Acked-by: Alexei Starovoitov 
Acked-by: Ingo Molnar 
Signed-off-by: Josef Bacik 
---
 arch/Kconfig |  3 +++
 arch/x86/Kconfig |  1 +
 arch/x86/include/asm/kprobes.h   |  4 +++
 arch/x86/include/asm/ptrace.h|  5 
 arch/x86/kernel/kprobes/ftrace.c | 14 ++
 include/linux/filter.h   |  3 ++-
 include/linux/trace_events.h |  1 +
 include/uapi/linux/bpf.h |  7 -
 kernel/bpf/core.c|  3 +++
 kernel/bpf/verifier.c|  2 ++
 kernel/events/core.c |  7 +
 kernel/trace/Kconfig | 11 
 kernel/trace/bpf_trace.c | 38 +++
 kernel/trace/trace_kprobe.c  | 55 +++-
 kernel/trace/trace_probe.h   | 12 +
 15 files changed, 157 insertions(+), 9 deletions(-)

diff --git a/arch/Kconfig b/arch/Kconfig
index d789a89cb32c..4fb618082259 100644
--- a/arch/Kconfig
+++ b/arch/Kconfig
@@ -195,6 +195,9 @@ config HAVE_OPTPROBES
 config HAVE_KPROBES_ON_FTRACE
bool
 
+config HAVE_KPROBE_OVERRIDE
+   bool
+
 config HAVE_NMI
bool
 
diff --git a/arch/x86/Kconfig b/arch/x86/Kconfig
index 971feac13506..5126d2750dd0 100644
--- a/arch/x86/Kconfig
+++ b/arch/x86/Kconfig
@@ -152,6 +152,7 @@ config X86
select HAVE_KERNEL_XZ
select HAVE_KPROBES
select HAVE_KPROBES_ON_FTRACE
+   select HAVE_KPROBE_OVERRIDE
select HAVE_KRETPROBES
select HAVE_KVM
select HAVE_LIVEPATCH   if X86_64
diff --git a/arch/x86/include/asm/kprobes.h b/arch/x86/include/asm/kprobes.h
index 6cf65437b5e5..c6c3b1f4306a 100644
--- a/arch/x86/include/asm/kprobes.h
+++ b/arch/x86/include/asm/kprobes.h
@@ -67,6 +67,10 @@ 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
+
 /* Architecture specific copy of original instruction*/
 struct arch_specific_insn {
/* copy of the original instruction */
diff --git a/arch/x86/include/asm/ptrace.h b/arch/x86/include/asm/ptrace.h
index 91c04c8e67fa..f04e71800c2f 100644
--- a/arch/x86/include/asm/ptrace.h
+++ b/arch/x86/include/asm/ptrace.h
@@ -108,6 +108,11 @@ static inline unsigned long regs_return_value(struct 
pt_regs *regs)
return regs->ax;
 }
 
+static inline void regs_set_return_value(struct pt_regs *regs, unsigned long 
rc)
+{
+   regs->ax = rc;
+}
+
 /*
  * user_mode(regs) determines whether a register set came from user
  * mode.  On x86_32, this is true if V8086 mode was enabled OR if the
diff --git a/arch/x86/kernel/kprobes/ftrace.c b/arch/x86/kernel/kprobes/ftrace.c
index 041f7b6dfa0f..3c455bf490cb 100644
--- a/arch/x86/kernel/kprobes/ftrace.c
+++ b/arch/x86/kernel/kprobes/ftrace.c
@@ -97,3 +97,17 @@ 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/include/linux/filter.h b/include/linux/filter.h
index cdd78a7beaae..dfa44fd74bae 100644
--- a/include/linux/filter.h
+++ b/include/linux/filter.h
@@ -458,7 +458,8 @@ struct bpf_prog {
locked:1,   /* Program image locked? */
gpl_compatible:1, /* Is filter GPL compatible? 
*/
cb_access:1,/* Is control block accessed? */
-   dst_needed:1;   /* Do we need dst entry? */
+   dst_needed:1,   /* Do we need dst entry? */
+   kprobe_override:1; /* Do we override a kprobe? 
*/
kmemcheck_bitfield_end(meta);
enum bpf_prog_type  type;   /* Type of BPF program */
u32 len;/* Number of filter blocks */
diff --git a/include/linux/trace_events.h b/include/linux/trace_events.h
index