[PATCH -tip v5 2/2] [BUGFIX] kprobes/x86: Do not jump-optimize kprobes on irq entry code

[Masami Hiramatsu <mhiramat@kernel.org>]

Since the kernel segment registers are not prepared at the
entry of 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@kernel.org>
Reported-by: Francis Deslauriers <francis.deslauriers@efficios.com>
Tested-by: Francis Deslauriers <francis.deslauriers@efficios.com>
---
 Changes in v5:
  - Use CONFIG_IRQENTRY.
---
 arch/Kconfig                  |    1 +
 arch/x86/kernel/kprobes/opt.c |    9 ++++++---
 2 files changed, 7 insertions(+), 3 deletions(-)

diff --git a/arch/Kconfig b/arch/Kconfig
index 21d0089117fe..f006af0d8c9e 100644
--- a/arch/Kconfig
+++ b/arch/Kconfig
@@ -91,6 +91,7 @@ config OPTPROBES
 	def_bool y
 	depends on KPROBES && HAVE_OPTPROBES
 	depends on !PREEMPT
+	select IRQENTRY
 
 config KPROBES_ON_FTRACE
 	def_bool y
diff --git a/arch/x86/kernel/kprobes/opt.c b/arch/x86/kernel/kprobes/opt.c
index 69ea0bc1cfa3..c26e7f989c7d 100644
--- a/arch/x86/kernel/kprobes/opt.c
+++ b/arch/x86/kernel/kprobes/opt.c
@@ -29,6 +29,7 @@
 #include <linux/kallsyms.h>
 #include <linux/ftrace.h>
 #include <linux/frame.h>
+#include <linux/interrupt.h>
 
 #include <asm/text-patching.h>
 #include <asm/cacheflush.h>
@@ -251,10 +252,12 @@ static int can_optimize(unsigned long paddr)
 
 	/*
 	 * Do not optimize in the entry code due to the unstable
-	 * stack handling.
+	 * stack handling and registers setup.
 	 */
-	if ((paddr >= (unsigned long)__entry_text_start) &&
-	    (paddr <  (unsigned long)__entry_text_end))
+	if (((paddr >= (unsigned long)__entry_text_start) &&
+	     (paddr <  (unsigned long)__entry_text_end)) ||
+	    ((paddr >= (unsigned long)__irqentry_text_start) &&
+	     (paddr <  (unsigned long)__irqentry_text_end)))
 		return 0;
 
 	/* Check there is enough space for a relative jump. */