Re: [PATCH 0/2] kprobe: Fix: add symbols to kprobe blacklist

[Masami Hiramatsu]

On Sun, 16 Jul 2017 23:37:44 +0900
Masami Hiramatsu <mhiramat@xxxxxxxxxx> wrote:

> So, the story what the stack said,
> 
> - optimized_callback() calls get_kprobe_ctlblk(), and this_cpu_ptr(&kprobe_ctlblk) caused a page fault (in apic_timer_interrupt, does it cause any problem?)
> - and following call-chain occured
>   async_page_fault -> error_entry -> trace_hardirqs_off_thunk -> 
>   trace_hardirqs_off_caller
> - "mov    %gs:0xc400,%rdx" caused async_page_fault() again.
> 
> Since trace_hardirqs_off_thunk() stores general registers on
> the stack, there are some noises.
> 
> [  114.429637] FS:  00000000021e7880(0000) GS:ffff88001fd40000(0000) knlGS:0000000000000000
> 
> So, the problem seems that cpu can not access to per-cpu pages.

OK, I got the root cause of this issue. Since at the irqentry code,
segment registers are not prepared for kernel yet (e.g. interrupted
in user-mode), so we must not optimize it.
I found we had already checked that by checking __entry_text_start/end,
but that is not enough, we need irqentry_text check too.

Here I made another patch, please try it.

-----
kprobes/x86: Do not jump-optimize kprobes on irq entry code

From: Masami Hiramatsu <mhiramat@xxxxxxxxxx>

Since the segment registers are not prepared for kernel
in the irq-entry code, if a kprobe on such code is
jump-optimized, accessing per-cpu variables may cause
kernel panic.
However, if the kprobe is not optimized, it kicks int3
exception and set segment registers correctly.

This checks probe-address and if it is in irq-entry code,
it prohibits optimizing such kprobes. This means we can
continuously probing such interrupt handlers by kprobes
but it is not optimized anymore.

Signed-off-by: Masami Hiramatsu <mhiramat@xxxxxxxxxx>
Reported-by: Francis Deslauriers <francis.deslauriers@xxxxxxxxxxxx>
---
 arch/x86/entry/entry_64.S      |    2 +-
 arch/x86/include/asm/unwind.h  |    1 +
 arch/x86/kernel/kprobes/opt.c  |    4 ++--
 arch/x86/kernel/unwind_frame.c |    4 ++--
 4 files changed, 6 insertions(+), 5 deletions(-)

diff --git a/arch/x86/entry/entry_64.S b/arch/x86/entry/entry_64.S
index a9a8027..95bca8b 100644
--- a/arch/x86/entry/entry_64.S
+++ b/arch/x86/entry/entry_64.S
@@ -675,7 +675,7 @@ apicinterrupt3 \num trace(\sym) smp_trace(\sym)
 #endif
 
 /* Make sure APIC interrupt handlers end up in the irqentry section: */
-#if defined(CONFIG_FUNCTION_GRAPH_TRACER) || defined(CONFIG_KASAN)
+#if defined(CONFIG_FUNCTION_GRAPH_TRACER) || defined(CONFIG_KASAN) || defined(CONFIG_KPROBES)
 # define PUSH_SECTION_IRQENTRY	.pushsection .irqentry.text, "ax"
 # define POP_SECTION_IRQENTRY	.popsection
 #else
diff --git a/arch/x86/include/asm/unwind.h b/arch/x86/include/asm/unwind.h
index e667649..a9896fb9 100644
--- a/arch/x86/include/asm/unwind.h
+++ b/arch/x86/include/asm/unwind.h
@@ -28,6 +28,7 @@ void __unwind_start(struct unwind_state *state, struct task_struct *task,
 bool unwind_next_frame(struct unwind_state *state);
 
 unsigned long unwind_get_return_address(struct unwind_state *state);
+bool in_entry_code(unsigned long ip);
 
 static inline bool unwind_done(struct unwind_state *state)
 {
diff --git a/arch/x86/kernel/kprobes/opt.c b/arch/x86/kernel/kprobes/opt.c
index 69ea0bc..a51c144 100644
--- a/arch/x86/kernel/kprobes/opt.c
+++ b/arch/x86/kernel/kprobes/opt.c
@@ -39,6 +39,7 @@
 #include <asm/insn.h>
 #include <asm/debugreg.h>
 #include <asm/set_memory.h>
+#include <asm/unwind.h>
 
 #include "common.h"
 
@@ -253,8 +254,7 @@ static int can_optimize(unsigned long paddr)
 	 * Do not optimize in the entry code due to the unstable
 	 * stack handling.
 	 */
-	if ((paddr >= (unsigned long)__entry_text_start) &&
-	    (paddr <  (unsigned long)__entry_text_end))
+	if (in_entry_code(paddr))
 		return 0;
 
 	/* Check there is enough space for a relative jump. */
diff --git a/arch/x86/kernel/unwind_frame.c b/arch/x86/kernel/unwind_frame.c
index b9389d7..95123ce 100644
--- a/arch/x86/kernel/unwind_frame.c
+++ b/arch/x86/kernel/unwind_frame.c
@@ -84,14 +84,14 @@ static size_t regs_size(struct pt_regs *regs)
 	return sizeof(*regs);
 }
 
-static bool in_entry_code(unsigned long ip)
+bool in_entry_code(unsigned long ip)
 {
 	char *addr = (char *)ip;
 
 	if (addr >= __entry_text_start && addr < __entry_text_end)
 		return true;
 
-#if defined(CONFIG_FUNCTION_GRAPH_TRACER) || defined(CONFIG_KASAN)
+#if defined(CONFIG_FUNCTION_GRAPH_TRACER) || defined(CONFIG_KASAN) || defined(CONFIG_KPROBES)
 	if (addr >= __irqentry_text_start && addr < __irqentry_text_end)
 		return true;
 #endif
-- 
Masami Hiramatsu <mhiramat@xxxxxxxxxx>