x86/ptrace: Prevent truncation of bitmap size

The active() callback of the IO bitmap regset divides the IO bitmap size by
the word size (32/64 bit). As the I/O bitmap size is in bytes the active
check fails for bitmap sizes of 1-3 bytes on 32bit and 1-7 bytes on 64bit.

Use DIV_ROUND_UP() instead.

Signed-off-by: Thomas Gleixner <tglx@linutronix.de>
Reviewed-by: Ingo Molnar <mingo@kernel.org>
Reviewed-by: Andy Lutomirski <luto@kernel.org>

diff --git a/arch/x86/kernel/ptrace.c b/arch/x86/kernel/ptrace.c
index 3c5bbe8..7c52674 100644 (file)
--- a/arch/x86/kernel/ptrace.c
+++ b/arch/x86/kernel/ptrace.c
@@ -697,7 +697,7 @@ static int ptrace_set_debugreg(struct task_struct *tsk, int n,
 static int ioperm_active(struct task_struct *target,
                         const struct user_regset *regset)
 {
-       return target->thread.io_bitmap_max / regset->size;
+       return DIV_ROUND_UP(target->thread.io_bitmap_max, regset->size);
 }
 
 static int ioperm_get(struct task_struct *target,