linux-kernel - Re: [PATCH 03/11] signal/openrisc: Fix do_unaligned

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Date:   Fri, 12 Jan 2018 22:25:21 +0900
From:   Stafford Horne <shorne@...il.com>
To:     "Eric W. Biederman" <ebiederm@...ssion.com>
Cc:     linux-kernel@...r.kernel.org, Al Viro <viro@...iv.linux.org.uk>,
        Oleg Nesterov <oleg@...hat.com>, linux-arch@...r.kernel.org,
        stable@...r.kernel.org, Jonas Bonn <jonas@...thpole.se>,
        Stefan Kristiansson <stefan.kristiansson@...nalahti.fi>,
        Arnd Bergmann <arnd@...db.de>, openrisc@...ts.librecores.org
Subject: Re: [PATCH 03/11] signal/openrisc: Fix do_unaligned_access to send
 the proper signal

On Thu, Jan 11, 2018 at 06:59:32PM -0600, Eric W. Biederman wrote:
> While reviewing the signal sending on openrisc the do_unaligned_access
> function stood out because it is obviously wrong.  A comment about an
> si_code set above when actually si_code is never set.  Leading to a
> random si_code being sent to userspace in the event of an unaligned
> access.
> 
> Looking further SIGBUS BUS_ADRALN is the proper pair of signal and
> si_code to send for an unaligned access. That is what other
> architectures do and what is required by posix.
> 
> Given that do_unaligned_access is broken in a way that no one can be
> relying on it on openrisc fix the code to just do the right thing.

Thanks, this looks good to me.

Acked-by: Stafford Horne <shorne@...il.com>

I see you have a series of related issues, so I guess you want to get them
merged together.  Let me know if I should put this patch onto my queue
seperately.

Trivia: this looks to have been copied from the mm page fault handling code,
hence the strange comment.

  $ grep -r "info.si_code has been set above" arch/
  arch/cris/mm/fault.c:           /* info.si_code has been set above */
  arch/m32r/mm/fault.c:           /* info.si_code has been set above */
  arch/mn10300/mm/fault.c:                /* info.si_code has been set above */
  arch/openrisc/mm/fault.c:               /* info.si_code has been set above */
  arch/openrisc/kernel/traps.c:           /* info.si_code has been set above */
  arch/arc/mm/fault.c:            /* info.si_code has been set above */
  arch/xtensa/mm/fault.c:         /* info.si_code has been set above */
  arch/mips/mm/fault.c:           /* info.si_code has been set above */
  arch/score/mm/fault.c:          /* info.si_code has been set above */
  arch/frv/mm/fault.c:            /* info.si_code has been set above */

-Stafford

> Cc: stable@...r.kernel.org
> Fixes: 769a8a96229e ("OpenRISC: Traps")
> Cc: Jonas Bonn <jonas@...thpole.se>
> Cc: Stefan Kristiansson <stefan.kristiansson@...nalahti.fi>
> Cc: Stafford Horne <shorne@...il.com>
> Cc: Arnd Bergmann <arnd@...db.de>
> Cc: openrisc@...ts.librecores.org
> Signed-off-by: "Eric W. Biederman" <ebiederm@...ssion.com>
> ---
>  arch/openrisc/kernel/traps.c | 10 +++++-----
>  1 file changed, 5 insertions(+), 5 deletions(-)
> 
> diff --git a/arch/openrisc/kernel/traps.c b/arch/openrisc/kernel/traps.c
> index 4085d72fa5ae..9e38dc66c9e4 100644
> --- a/arch/openrisc/kernel/traps.c
> +++ b/arch/openrisc/kernel/traps.c
> @@ -266,12 +266,12 @@ asmlinkage void do_unaligned_access(struct pt_regs *regs, unsigned long address)
>  	siginfo_t info;
>  
>  	if (user_mode(regs)) {
> -		/* Send a SIGSEGV */
> -		info.si_signo = SIGSEGV;
> +		/* Send a SIGBUS */
> +		info.si_signo = SIGBUS;
>  		info.si_errno = 0;
> -		/* info.si_code has been set above */
> -		info.si_addr = (void *)address;
> -		force_sig_info(SIGSEGV, &info, current);
> +		info.si_code = BUS_ADRALN;
> +		info.si_addr = (void __user *)address;
> +		force_sig_info(SIGBUS, &info, current);
>  	} else {
>  		printk("KERNEL: Unaligned Access 0x%.8lx\n", address);
>  		show_registers(regs);
> -- 
> 2.14.1
>