linux-kernel - Re: [PATCH 8/8] membarrier: Rewrite sync_core_before

lists.openwall.net		lists / announce owl-users owl-dev john-users john-dev passwdqc-users yescrypt popa3d-users / oss-security kernel-hardening musl sabotage tlsify passwords / crypt-dev xvendor / Bugtraq Full-Disclosure linux-kernel linux-netdev linux-ext4 linux-hardening linux-cve-announce PHC
Open Source and information security mailing list archives

Hash Suite: Windows password security audit tool. GUI, reports in PDF.

[<prev] [next>] [<thread-prev] [thread-next>] [day] [month] [year] [list]

Date:   Thu, 17 Jun 2021 17:12:15 -0700
From:   Andy Lutomirski <luto@...nel.org>
To:     Mathieu Desnoyers <mathieu.desnoyers@...icios.com>
Cc:     x86 <x86@...nel.org>, Dave Hansen <dave.hansen@...el.com>,
        linux-kernel <linux-kernel@...r.kernel.org>,
        linux-mm <linux-mm@...ck.org>,
        Andrew Morton <akpm@...ux-foundation.org>,
        Michael Ellerman <mpe@...erman.id.au>,
        Benjamin Herrenschmidt <benh@...nel.crashing.org>,
        Paul Mackerras <paulus@...ba.org>,
        linuxppc-dev <linuxppc-dev@...ts.ozlabs.org>,
        Nicholas Piggin <npiggin@...il.com>,
        Catalin Marinas <catalin.marinas@....com>,
        Will Deacon <will@...nel.org>,
        linux-arm-kernel <linux-arm-kernel@...ts.infradead.org>,
        Peter Zijlstra <peterz@...radead.org>,
        stable <stable@...r.kernel.org>
Subject: Re: [PATCH 8/8] membarrier: Rewrite sync_core_before_usermode() and
 improve documentation

On 6/17/21 7:47 AM, Mathieu Desnoyers wrote:

> Please change back this #ifndef / #else / #endif within function for
> 
> if (!IS_ENABLED(CONFIG_ARCH_HAS_MEMBARRIER_SYNC_CORE)) {
>   ...
> } else {
>   ...
> }
> 
> I don't think mixing up preprocessor and code logic makes it more readable.

I agree, but I don't know how to make the result work well.
membarrier_sync_core_before_usermode() isn't defined in the !IS_ENABLED
case, so either I need to fake up a definition or use #ifdef.

If I faked up a definition, I would want to assert, at build time, that
it isn't called.  I don't think we can do:

static void membarrier_sync_core_before_usermode()
{
    BUILD_BUG_IF_REACHABLE();
}