linux-kernel - Re: [PATCH] x86: Fix 32-bit compatible userspace write size overflow error

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Date:   Wed, 15 Nov 2023 20:31:20 -0800
From:   "H. Peter Anvin" <hpa@...or.com>
To:     Jinjie Ruan <ruanjinjie@...wei.com>, linux-kernel@...r.kernel.org,
        Thomas Gleixner <tglx@...utronix.de>,
        Ingo Molnar <mingo@...hat.com>, Borislav Petkov <bp@...en8.de>,
        Dave Hansen <dave.hansen@...ux.intel.com>, x86@...nel.org
Subject: Re: [PATCH] x86: Fix 32-bit compatible userspace write size overflow
 error

It's not clear to me that this is actually the correct behavior; the 
important thing is that it faults (as nothing is mapped above 4 GB anyway.)

	-hpa


On 11/15/23 02:56, Jinjie Ruan wrote:
> For 32-bit compatible userspace program, write with size = -1 return not
> -1 but unexpected other values, which is due to the __access_ok() check is
> insufficient. The specified "ptr + size" is greater than 32-bit limit and
> should return -EFAULT, but it is not checked and can not catch the overflow
> error.
> 
> Fix above error by checking 32-bit limit if it is 32-bit compatible
> userspace program.

	-hpa