linux-kernel - [patch V2 01/16] x86/ptrace: Prevent truncation of bitmap size

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Date:   Mon, 11 Nov 2019 23:03:15 +0100
From:   Thomas Gleixner <tglx@...utronix.de>
To:     LKML <linux-kernel@...r.kernel.org>
Cc:     x86@...nel.org, Linus Torvalds <torvalds@...uxfoundation.org>,
        Andy Lutomirski <luto@...nel.org>,
        Stephen Hemminger <stephen@...workplumber.org>,
        Willy Tarreau <w@....eu>, Juergen Gross <jgross@...e.com>,
        Sean Christopherson <sean.j.christopherson@...el.com>,
        "H. Peter Anvin" <hpa@...or.com>, Ingo Molnar <mingo@...nel.org>
Subject: [patch V2 01/16] x86/ptrace: Prevent truncation of bitmap size

From: Thomas Gleixner <tglx@...utronix.de>

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@...utronix.de>
Reviewed-by: Ingo Molnar <mingo@...nel.org>

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

--- a/arch/x86/kernel/ptrace.c
+++ b/arch/x86/kernel/ptrace.c
@@ -697,7 +697,7 @@ static int ptrace_set_debugreg(struct ta
 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,