linux-kernel - Re: [PATCH 2/2] sigaction.2: wfix

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Date:   Mon, 8 Mar 2021 22:30:40 +0100
From:   Borislav Petkov <bp@...en8.de>
To:     Yu-cheng Yu <yu-cheng.yu@...el.com>
Cc:     linux-man@...r.kernel.org,
        Alejandro Colomar <alx.manpages@...il.com>,
        Michael Kerrisk <mtk.manpages@...il.com>,
        Andy Lutomirski <luto@...nel.org>,
        Dave Hansen <dave.hansen@...ux.intel.com>,
        Florian Weimer <fweimer@...hat.com>,
        "H.J. Lu" <hjl.tools@...il.com>, linux-kernel@...r.kernel.org,
        linux-api@...r.kenel.org
Subject: Re: [PATCH 2/2] sigaction.2: wfix - Clarify si_addr description.

On Fri, Feb 26, 2021 at 09:26:34AM -0800, Yu-cheng Yu wrote:
> SIGSEGV fills si_addr only for memory access faults.  Add a note to clarify.
> 
> Signed-off-by: Yu-cheng Yu <yu-cheng.yu@...el.com>
> Cc: Alejandro Colomar <alx.manpages@...il.com>
> Cc: Michael Kerrisk <mtk.manpages@...il.com>
> Cc: Andy Lutomirski <luto@...nel.org>
> Cc: Borislav Petkov <bp@...en8.de>
> Cc: Dave Hansen <dave.hansen@...ux.intel.com>
> Cc: Florian Weimer <fweimer@...hat.com>
> Cc: "H.J. Lu" <hjl.tools@...il.com>
> Cc: linux-kernel@...r.kernel.org
> Cc: linux-api@...r.kenel.org
> Link: https://lore.kernel.org/linux-api/20210217222730.15819-7-yu-cheng.yu@intel.com/
> ---
>  man2/sigaction.2 | 7 ++++++-
>  1 file changed, 6 insertions(+), 1 deletion(-)
> 
> diff --git a/man2/sigaction.2 b/man2/sigaction.2
> index 49a30f11e..bea884a23 100644
> --- a/man2/sigaction.2
> +++ b/man2/sigaction.2
> @@ -467,7 +467,7 @@ and
>  .BR SIGTRAP
>  fill in
>  .I si_addr
> -with the address of the fault.
> +with the address of the fault (see notes).
>  On some architectures,
>  these signals also fill in the
>  .I si_trapno
> @@ -955,6 +955,11 @@ It is not possible to block
>  .IR sa_mask ).
>  Attempts to do so are silently ignored.
>  .PP
> +In a
> +.B SIGSEGV,
> +if the fault is a memory access fault, si_addr is filled with the address
> +causing the fault, otherwise it is not filled.

"... otherwise it is uninitialized." or "zeroed" or whatever...

And I'm having trouble figuring out why do you need to clarify this?

Because of this sentence:

       * SIGILL,  SIGFPE, SIGSEGV, SIGBUS, and SIGTRAP fill in si_addr with the address
         of the fault.  On some architectures, these signals also fill in the si_trapno
         field.

?

If so, did you audit all architectures whether si_addr is populated only
on memory access faults or is this something POSIX dictates or what's
up? Because the sigaction(2) manpage is arch-agnostic and this is a
rather strong assertion.

What am I missing?

Thx.

-- 
Regards/Gruss,
    Boris.

https://people.kernel.org/tglx/notes-about-netiquette