linux-kernel - Re: [PATCH glibc 5/9] glibc: Perform rseq(2) registration at C startup and thread creation (v17)

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Message-ID: <87ftcpxhpw.fsf@mid.deneb.enyo.de>
Date:   Mon, 27 Apr 2020 13:59:07 +0200
From:   Florian Weimer <fw@...eb.enyo.de>
To:     Mathieu Desnoyers via Libc-alpha <libc-alpha@...rceware.org>
Cc:     Carlos O'Donell <carlos@...hat.com>,
        Mathieu Desnoyers <mathieu.desnoyers@...icios.com>,
        Rich Felker <dalias@...c.org>, linux-api@...r.kernel.org,
        Boqun Feng <boqun.feng@...il.com>,
        Will Deacon <will.deacon@....com>,
        linux-kernel@...r.kernel.org,
        Peter Zijlstra <peterz@...radead.org>,
        Ben Maurer <bmaurer@...com>, Dave Watson <davejwatson@...com>,
        Thomas Gleixner <tglx@...utronix.de>,
        "Paul E. McKenney" <paulmck@...ux.vnet.ibm.com>,
        Paul Turner <pjt@...gle.com>,
        Joseph Myers <joseph@...esourcery.com>
Subject: Re: [PATCH glibc 5/9] glibc: Perform rseq(2) registration at C startup and thread creation (v17)

* Mathieu Desnoyers via Libc-alpha:

> diff --git a/elf/libc_early_init.c b/elf/libc_early_init.c
> index 1ac66d895d..30466afea0 100644
> --- a/elf/libc_early_init.c
> +++ b/elf/libc_early_init.c
> @@ -18,10 +18,13 @@
>  
>  #include <ctype.h>
>  #include <libc-early-init.h>
> +#include <rseq-internal.h>
>  
>  void
>  __libc_early_init (void)
>  {
>    /* Initialize ctype data.  */
>    __ctype_init ();
> +  /* Register rseq ABI to the kernel.   */
> +  (void) rseq_register_current_thread ();
>  }

I think the registration must be restricted to the primary namespace.
Otherwise, LD_AUDIT will register the area to the secondary libc (in
the audit module), not the primary libc for the entire process.

I think the easiest way to implement this for now is a flag argument
for __libc_early_init (as the upstream __libc_multiple_libcs is not
entirely accurate).  I will submit a patch.