kprobes/x86: Check for invalid ftrace location in __recover_probed_insn()

__recover_probed_insn() should always be called from an address
where an instructions starts. The check for ftrace_location()
might help to discover a potential inconsistency.

This patch adds WARN_ON() when the inconsistency is detected.
Also it adds handling of the situation when the original code
can not get recovered.

Suggested-by: Masami Hiramatsu <masami.hiramatsu.pt@hitachi.com>
Signed-off-by: Petr Mladek <pmladek@suse.cz>
Cc: Ananth NMavinakayanahalli <ananth@in.ibm.com>
Cc: Anil S Keshavamurthy <anil.s.keshavamurthy@intel.com>
Cc: David S. Miller <davem@davemloft.net>
Cc: Frederic Weisbecker <fweisbec@gmail.com>
Cc: Jiri Kosina <jkosina@suse.cz>
Cc: Steven Rostedt <rostedt@goodmis.org>
Link: http://lkml.kernel.org/r/1424441250-27146-3-git-send-email-pmladek@suse.cz
Signed-off-by: Ingo Molnar <mingo@kernel.org>

2 files changed, 14 insertions, 0 deletions

diff --git a/arch/x86/kernel/kprobes/core.c b/arch/x86/kernel/kprobes/core.c
index c3b4b46b4797..4e3d5a9621fe 100644
--- a/arch/x86/kernel/kprobes/core.c
+++ b/arch/x86/kernel/kprobes/core.c
@@ -228,6 +228,13 @@ __recover_probed_insn(kprobe_opcode_t *buf, unsigned long addr)
         kp = get_kprobe((void *)addr);
         faddr = ftrace_location(addr);
         /*
+         * Addresses inside the ftrace location are refused by
+         * arch_check_ftrace_location(). Something went terribly wrong
+         * if such an address is checked here.
+         */
+        if (WARN_ON(faddr && faddr != addr))
+                return 0UL;
+        /*
          * Use the current code if it is not modified by Kprobe
          * and it cannot be modified by ftrace.
          */
@@ -265,6 +272,7 @@ __recover_probed_insn(kprobe_opcode_t *buf, unsigned long addr)
  * Recover the probed instruction at addr for further analysis.
  * Caller must lock kprobes by kprobe_mutex, or disable preemption
  * for preventing to release referencing kprobes.
+ * Returns zero if the instruction can not get recovered.
  */
 unsigned long recover_probed_instruction(kprobe_opcode_t *buf, unsigned long addr)
 {
@@ -299,6 +307,8 @@ static int can_probe(unsigned long paddr)
                  * normally used, we just go through if there is no kprobe.
                  */
                 __addr = recover_probed_instruction(buf, addr);
+                if (!__addr)
+                        return 0;
                 kernel_insn_init(&insn, (void *)__addr, MAX_INSN_SIZE);
                 insn_get_length(&insn);
 
@@ -347,6 +357,8 @@ int __copy_instruction(u8 *dest, u8 *src)
         unsigned long recovered_insn =
                 recover_probed_instruction(buf, (unsigned long)src);
 
+        if (!recovered_insn)
+                return 0;
         kernel_insn_init(&insn, (void *)recovered_insn, MAX_INSN_SIZE);
         insn_get_length(&insn);
         /* Another subsystem puts a breakpoint, failed to recover */
diff --git a/arch/x86/kernel/kprobes/opt.c b/arch/x86/kernel/kprobes/opt.c
index 7c523bbf3dc8..3aef248ec1ee 100644
--- a/arch/x86/kernel/kprobes/opt.c
+++ b/arch/x86/kernel/kprobes/opt.c
@@ -259,6 +259,8 @@ static int can_optimize(unsigned long paddr)
                          */
                         return 0;
                 recovered_insn = recover_probed_instruction(buf, addr);
+                if (!recovered_insn)
+                        return 0;
                 kernel_insn_init(&insn, (void *)recovered_insn, MAX_INSN_SIZE);
                 insn_get_length(&insn);
                 /* Another subsystem puts a breakpoint */