linux-kernel - Re: [PATCH 06/10] signal: Helpers for faults with specialized siginfo layouts

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Date:   Wed, 24 Jan 2018 14:54:06 -0600
From:   ebiederm@...ssion.com (Eric W. Biederman)
To:     Ram Pai <linuxram@...ibm.com>
Cc:     linux-kernel@...r.kernel.org, Al Viro <viro@...iv.linux.org.uk>,
        Oleg Nesterov <oleg@...hat.com>, linux-arch@...r.kernel.org
Subject: Re: [PATCH 06/10] signal: Helpers for faults with specialized siginfo layouts

Ram Pai <linuxram@...ibm.com> writes:

> On Tue, Jan 23, 2018 at 03:07:15PM -0600, Eric W. Biederman wrote:
>> The helpers added are:
>> send_sig_mceerr
>> force_sig_mceerr
>> force_sig_bnderr
>> force_sig_pkuerr
>> 
>> Filling out siginfo properly can ge tricky.  Especially for these
>> specialized cases where the temptation is to share code with other
>> cases which use a different subset of siginfo fields.  Unfortunately
>> that code sharing frequently results in bugs with the wrong siginfo
>> fields filled in, and makes it harder to verify that the siginfo
>> structure was properly initialized.
>> 
>> Provide these helpers instead that get all of the details right, and
>> guarantee that siginfo is properly initialized.
>> 
>> send_sig_mceerr and force_sig_mceer are a little special as two si
>> codes BUS_MCEERR_AO and BUS_MCEER_AR both use the same extended
>> signinfo layout.
>
> nice. i can make use of these helpers in the memory-key implementation.
>
> One small nit-pick below though...
>
>> 
>> Signed-off-by: "Eric W. Biederman" <ebiederm@...ssion.com>
>> ---
>>  include/linux/sched/signal.h |  6 +++++
>>  kernel/signal.c              | 61 ++++++++++++++++++++++++++++++++++++++++++++
>>  2 files changed, 67 insertions(+)
>> 
>> diff --git a/include/linux/sched/signal.h b/include/linux/sched/signal.h
>
> ...snip..
>
>> +
>> +#ifdef SEGV_PKUERR
>
> Should this really be under SEGV_PKUERR ?  that macro is defined
> unconditionally anyway.

Unless you are running my unified siginfo.h (from an earlier patchset
which I build upon).  It turns out that ia64 has a conflict for that
number.  So ia64 really can't use the define and this infrastructure.

We might decide to sort that out and always have SEGV_PKUERR always
defined.  Sadly for the moment the #ifdef is necessary. 

>> +int force_sig_pkuerr(void __user *addr, u32 pkey)
>> +{
>> +	struct siginfo info;
>> +
>> +	clear_siginfo(&info);
>> +	info.si_signo = SIGSEGV;
>> +	info.si_errno = 0;
>> +	info.si_code  = SEGV_PKUERR;
>> +	info.si_addr  = addr;
>> +	info.si_pkey  = pkey;
>> +	return force_sig_info(info.si_signo, &info, current);
>> +}
>> +#endif

Eric