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Date:   Tue, 18 May 2021 07:40:29 +0100
From:   Christoph Hellwig <hch@infradead.org>
To:     "Eric W. Biederman" <ebiederm@xmission.com>
Cc:     Arnd Bergmann <arnd@kernel.org>, linux-arch@vger.kernel.org,
        Arnd Bergmann <arnd@arndb.de>,
        Christoph Hellwig <hch@infradead.org>,
        Alexander Viro <viro@zeniv.linux.org.uk>,
        Andrew Morton <akpm@linux-foundation.org>,
        Borislav Petkov <bp@alien8.de>,
        Brian Gerst <brgerst@gmail.com>,
        Ingo Molnar <mingo@kernel.org>,
        "H. Peter Anvin" <hpa@zytor.com>,
        Thomas Gleixner <tglx@linutronix.de>,
        Linux ARM <linux-arm-kernel@lists.infradead.org>,
        linux-kernel@vger.kernel.org, Linux-MM <linux-mm@kvack.org>,
        kexec@lists.infradead.org
Subject: Re: [PATCH v3 1/4] kexec: simplify compat_sys_kexec_load
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 <20210517203343.3941777-2-arnd@kernel.org>
 <m1y2cc3d97.fsf@fess.ebiederm.org>
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On Mon, May 17, 2021 at 10:57:24PM -0500, Eric W. Biederman wrote:
> We open ourselves up to bugs whenever we lie to the type system.
> 
> Skimming through the code it looks like it should be possible
> to not need the in_compat_syscall and the casts to the wrong
> type by changing the order of the code a little bit.

What kind of bug do you expect?  We must only copy from user addresses
once anyway.  I've never seen bugs due the use of in_compat_syscall,
but plenty due to cruft code trying to avoid it.