linux-kernel - Re: [PATCH v2 0/2] Lock and Pointer guards

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Message-ID: <e7095f56-44c4-7cf1-69f5-4ff66d20952c@redhat.com>
Date:   Fri, 9 Jun 2023 12:20:53 +0200
From:   Paolo Bonzini <pbonzini@...hat.com>
To:     Nick Desaulniers <ndesaulniers@...gle.com>,
        Peter Zijlstra <peterz@...radead.org>
Cc:     Kees Cook <keescook@...omium.org>,
        Linus Torvalds <torvalds@...ux-foundation.org>,
        gregkh@...uxfoundation.org, linux-kernel@...r.kernel.org,
        ojeda@...nel.org, mingo@...hat.com, will@...nel.org,
        longman@...hat.com, boqun.feng@...il.com, juri.lelli@...hat.com,
        vincent.guittot@...aro.org, dietmar.eggemann@....com,
        rostedt@...dmis.org, bsegall@...gle.com, mgorman@...e.de,
        bristot@...hat.com, vschneid@...hat.com, paulmck@...nel.org,
        frederic@...nel.org, quic_neeraju@...cinc.com,
        joel@...lfernandes.org, josh@...htriplett.org,
        mathieu.desnoyers@...icios.com, jiangshanlai@...il.com,
        rcu@...r.kernel.org, tj@...nel.org, tglx@...utronix.de,
        linux-toolchains@...r.kernel.org
Subject: Re: [PATCH v2 0/2] Lock and Pointer guards

On 6/8/23 22:14, Nick Desaulniers wrote:
> Here, we're talking about using __attribute__((cleanup())) to DTR
> locally, but then we return a "raw" pointer to a caller. What cleanup
> function should the caller run, implicitly, if at all?  If we use
> __attribute__((cleanup())) that saves us a few gotos locally, but the
> caller perhaps now needs the same treatment.

But this is only a problem when you return a void*; and in general in C 
you will return a struct more often than a raw pointer (and in C++ you 
also have the issue of delete vs. delete[], that does not exist in C).

Returning a struct doesn't protect against use-after-free bugs in the 
way std::unique_ptr<> or Rust lifetimes do, but it at least tries to 
protect against calling the wrong cleanup function if you provide a 
typed "destructor" function that does the right thing---for example by 
handling reference counting or by freeing sub-structs before calling 
kfree/vfree.

Of course it's not a silver bullet, but then that's why people are 
looking into Rust for Linux.

Paolo