[tip: x86/iopl] x86/ptrace: Prevent truncation of bitmap size

[tip-bot2 for Thomas Gleixner]

The following commit has been merged into the x86/iopl branch of tip:

Commit-ID:     c5d623b17c2424272b3355a524b094ff02cfd9aa
Gitweb:        https://git.kernel.org/tip/c5d623b17c2424272b3355a524b094ff02cfd9aa
Author:        Thomas Gleixner <tglx@xxxxxxxxxxxxx>
AuthorDate:    Wed, 13 Nov 2019 21:42:41 +01:00
Committer:     Thomas Gleixner <tglx@xxxxxxxxxxxxx>
CommitterDate: Thu, 14 Nov 2019 20:14:59 +01:00

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@xxxxxxxxxxxxx>
Reviewed-by: Ingo Molnar <mingo@xxxxxxxxxx>
Reviewed-by: Andy Lutomirski <luto@xxxxxxxxxx>
Acked-by: Peter Zijlstra (Intel) <peterz@xxxxxxxxxxxxx>
Link: https://lkml.kernel.org/r/20191113210103.819769574@xxxxxxxxxxxxx



---
 arch/x86/kernel/ptrace.c | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/arch/x86/kernel/ptrace.c b/arch/x86/kernel/ptrace.c
index 3c5bbe8..7c52674 100644
--- 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,