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Date:   Sat, 5 Sep 2020 12:24:38 +0100
From:   Matthew Wilcox <willy@infradead.org>
To:     Gabriel Krisman Bertazi <krisman@collabora.com>
Cc:     luto@kernel.org, tglx@linutronix.de, keescook@chromium.org,
        x86@kernel.org, linux-kernel@vger.kernel.org,
        linux-api@vger.kernel.org, linux-kselftest@vger.kernel.org,
        shuah@kernel.org, kernel@collabora.com,
        Paul Gofman <gofmanp@gmail.com>
Subject: Re: [PATCH v6 5/9] kernel: Implement selective syscall userspace
 redirection
Message-ID: <20200905112438.GA16750@casper.infradead.org>
References: <20200904203147.2908430-1-krisman@collabora.com>
 <20200904203147.2908430-6-krisman@collabora.com>
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On Fri, Sep 04, 2020 at 04:31:43PM -0400, Gabriel Krisman Bertazi wrote:
> +int set_syscall_user_dispatch(int mode, unsigned long dispatcher_start,
> +			      unsigned long dispatcher_end, char __user *selector)
> +{
> +	switch (mode) {
> +	case PR_SYS_DISPATCH_OFF:
...
> +	case PR_SYS_DISPATCH_ON:
...
> +	default:
> +		return -EINVAL;
...
> +	case PR_SET_SYSCALL_USER_DISPATCH:
> +		error = set_syscall_user_dispatch((int) arg2, arg3, arg4,
> +						  (char __user *) arg5);

This makes aliases of DISPATCH_OFF and DISPATCH_ON every 4GB throughout
the 64-bit space of arg2.  I don't think that was intentional (nor
desirable).  I'd suggest just making 'mode' a long and dropping the cast.