linux-kernel - Re: [PATCH v2] x86: signal: move save_altstack

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Date:   Sat, 4 Apr 2020 18:01:00 +0200
From:   Oleg Nesterov <oleg@...hat.com>
To:     Nick Desaulniers <ndesaulniers@...gle.com>
Cc:     tglx@...utronix.de, mingo@...hat.com, bp@...en8.de,
        Peter Zijlstra <peterz@...radead.org>,
        clang-built-linux@...glegroups.com,
        Linus Torvalds <torvalds@...ux-foundation.org>,
        "H. Peter Anvin" <hpa@...or.com>, x86@...nel.org,
        Al Viro <viro@...iv.linux.org.uk>,
        Sebastian Andrzej Siewior <bigeasy@...utronix.de>,
        Andy Lutomirski <luto@...nel.org>,
        Sami Tolvanen <samitolvanen@...gle.com>,
        Marco Elver <elver@...gle.com>,
        Brian Gerst <brgerst@...il.com>, Arnd Bergmann <arnd@...db.de>,
        Andrew Morton <akpm@...ux-foundation.org>,
        "Eric W. Biederman" <ebiederm@...ssion.com>,
        linux-kernel@...r.kernel.org
Subject: Re: [PATCH v2] x86: signal: move save_altstack_ex out of generic
 headers

On 04/03, Nick Desaulniers wrote:
>
> --- a/arch/x86/kernel/signal.c
> +++ b/arch/x86/kernel/signal.c
> @@ -416,6 +416,7 @@ static int __setup_rt_frame(int sig, struct ksignal *ksig,
>  	return 0;
>  Efault:
>  	user_access_end();
> +	reset_altstack();
>  	return -EFAULT;
>  }
>  #else /* !CONFIG_X86_32 */
> @@ -507,6 +508,7 @@ static int __setup_rt_frame(int sig, struct ksignal *ksig,
>  
>  Efault:
>  	user_access_end();
> +	reset_altstack();
>  	return -EFAULT;
>  }

I must have missed something, but this looks just wrong.

reset_altstack() should be called when __setup_rt_frame() (and
unsafe_save_altstack() in particular) succeeds, not when it fails.

Nevermind, Al has already suggested to use signal_delivered()...

Oleg.