kprobes/x86: Use copy_from_kernel_nofault() to read from unsafe address

Read from an unsafe address with copy_from_kernel_nofault() in
arch_adjust_kprobe_addr() because this function is used before checking
the address is in text or not. Syzcaller bot found a bug and reported
the case if user specifies inaccessible data area,
arch_adjust_kprobe_addr() will cause a kernel panic.

[ mingo: Clarified the comment. ]

Fixes: cc66bb914578 ("x86/ibt,kprobes: Cure sym+0 equals fentry woes")
Reported-by: Qiang Zhang <zzqq0103.hey@gmail.com>
Tested-by: Jinghao Jia <jinghao7@illinois.edu>
Signed-off-by: Masami Hiramatsu (Google) <mhiramat@kernel.org>
Signed-off-by: Ingo Molnar <mingo@kernel.org>
Link: https://lore.kernel.org/r/171042945004.154897.2221804961882915806.stgit@devnote2

diff --git a/arch/x86/kernel/kprobes/core.c b/arch/x86/kernel/kprobes/core.c
index 091b3ab76a1801bbfa1c9f61bdbf45dc95bb8026..d0e49bd7c6f3faced07c7527b3e8df4f0e2dbe79 100644 (file)
--- a/arch/x86/kernel/kprobes/core.c
+++ b/arch/x86/kernel/kprobes/core.c
@@ -373,7 +373,16 @@ out:
 kprobe_opcode_t *arch_adjust_kprobe_addr(unsigned long addr, unsigned long offset,
                                         bool *on_func_entry)
 {
-       if (is_endbr(*(u32 *)addr)) {
+       u32 insn;
+
+       /*
+        * Since 'addr' is not guaranteed to be safe to access, use
+        * copy_from_kernel_nofault() to read the instruction:
+        */
+       if (copy_from_kernel_nofault(&insn, (void *)addr, sizeof(u32)))
+               return NULL;
+
+       if (is_endbr(insn)) {
                *on_func_entry = !offset || offset == 4;
                if (*on_func_entry)
                        offset = 4;