linux-kernel - Re: [PATCH v3 1/4] kexec: simplify compat_sys_kexec

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Message-ID: <YKNhXQ883lRbqQGA@infradead.org>
Date:   Tue, 18 May 2021 07:40:29 +0100
From:   Christoph Hellwig <hch@...radead.org>
To:     "Eric W. Biederman" <ebiederm@...ssion.com>
Cc:     Arnd Bergmann <arnd@...nel.org>, linux-arch@...r.kernel.org,
        Arnd Bergmann <arnd@...db.de>,
        Christoph Hellwig <hch@...radead.org>,
        Alexander Viro <viro@...iv.linux.org.uk>,
        Andrew Morton <akpm@...ux-foundation.org>,
        Borislav Petkov <bp@...en8.de>,
        Brian Gerst <brgerst@...il.com>,
        Ingo Molnar <mingo@...nel.org>,
        "H. Peter Anvin" <hpa@...or.com>,
        Thomas Gleixner <tglx@...utronix.de>,
        Linux ARM <linux-arm-kernel@...ts.infradead.org>,
        linux-kernel@...r.kernel.org, Linux-MM <linux-mm@...ck.org>,
        kexec@...ts.infradead.org
Subject: Re: [PATCH v3 1/4] kexec: simplify compat_sys_kexec_load

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.