Re: [RFC PATCH 02/12] powerpc/kernel: Switch to using MAX_ERRNO

[Benjamin Herrenschmidt <benh@kernel.crashing.org>]

On Wed, 2015-07-15 at 17:37 +1000, Michael Ellerman wrote:
> Currently on powerpc we have our own #define for the highest (negative)
> errno value, called _LAST_ERRNO. This is defined to be 516, for reasons
> which are not clear.
> 
> The generic code, and x86, use MAX_ERRNO, which is defined to be 4095.
> 
> In particular seccomp uses MAX_ERRNO to restrict the value that a
> seccomp filter can return.
> 
> Currently with the mismatch between _LAST_ERRNO and MAX_ERRNO, a seccomp
> tracer wanting to return 600, expecting it to be seen as an error, would
> instead find on powerpc that userspace sees a successful syscall with a
> return value of 600.
> 
> To avoid this inconsistency, switch powerpc to use MAX_ERRNO.
> 
> We are somewhat confident that generic syscalls that can return a
> non-error value above negative MAX_ERRNO have already been updated to
> use force_successful_syscall_return().
> 
> I have also checked all the powerpc specific syscalls, and believe that
> none of them expect to return a non-error value between -MAX_ERRNO and
> -516. So this change should be safe ...
> 
> Signed-off-by: Michael Ellerman <mpe@ellerman.id.au>

Acked-by: Benjamin Herrenschmidt <benh@kernel.crashing.org>

> ---
>  arch/powerpc/include/uapi/asm/errno.h | 2 --
>  arch/powerpc/kernel/entry_32.S        | 3 ++-
>  arch/powerpc/kernel/entry_64.S        | 5 +++--
>  3 files changed, 5 insertions(+), 5 deletions(-)
> 
> diff --git a/arch/powerpc/include/uapi/asm/errno.h b/arch/powerpc/include/uapi/asm/errno.h
> index 8c145fd17d86..e8b6b5f7de7c 100644
> --- a/arch/powerpc/include/uapi/asm/errno.h
> +++ b/arch/powerpc/include/uapi/asm/errno.h
> @@ -6,6 +6,4 @@
>  #undef	EDEADLOCK
>  #define	EDEADLOCK	58	/* File locking deadlock error */
>  
> -#define _LAST_ERRNO	516
> -
>  #endif	/* _ASM_POWERPC_ERRNO_H */
> diff --git a/arch/powerpc/kernel/entry_32.S b/arch/powerpc/kernel/entry_32.S
> index 46fc0f4d8982..67ecdf61f4e3 100644
> --- a/arch/powerpc/kernel/entry_32.S
> +++ b/arch/powerpc/kernel/entry_32.S
> @@ -20,6 +20,7 @@
>   */
>  
>  #include <linux/errno.h>
> +#include <linux/err.h>
>  #include <linux/sys.h>
>  #include <linux/threads.h>
>  #include <asm/reg.h>
> @@ -354,7 +355,7 @@ ret_from_syscall:
>  	SYNC
>  	MTMSRD(r10)
>  	lwz	r9,TI_FLAGS(r12)
> -	li	r8,-_LAST_ERRNO
> +	li	r8,-MAX_ERRNO
>  	andi.	r0,r9,(_TIF_SYSCALL_DOTRACE|_TIF_SINGLESTEP|_TIF_USER_WORK_MASK|_TIF_PERSYSCALL_MASK)
>  	bne-	syscall_exit_work
>  	cmplw	0,r3,r8
> diff --git a/arch/powerpc/kernel/entry_64.S b/arch/powerpc/kernel/entry_64.S
> index 0796c487d3db..8292581a42f1 100644
> --- a/arch/powerpc/kernel/entry_64.S
> +++ b/arch/powerpc/kernel/entry_64.S
> @@ -19,6 +19,7 @@
>   */
>  
>  #include <linux/errno.h>
> +#include <linux/err.h>
>  #include <asm/unistd.h>
>  #include <asm/processor.h>
>  #include <asm/page.h>
> @@ -207,7 +208,7 @@ system_call:			/* label this so stack traces look sane */
>  #endif /* CONFIG_PPC_BOOK3E */
>  
>  	ld	r9,TI_FLAGS(r12)
> -	li	r11,-_LAST_ERRNO
> +	li	r11,-MAX_ERRNO
>  	andi.	r0,r9,(_TIF_SYSCALL_DOTRACE|_TIF_SINGLESTEP|_TIF_USER_WORK_MASK|_TIF_PERSYSCALL_MASK)
>  	bne-	syscall_exit_work
>  	cmpld	r3,r11
> @@ -279,7 +280,7 @@ syscall_exit_work:
>  	beq+	0f
>  	REST_NVGPRS(r1)
>  	b	2f
> -0:	cmpld	r3,r11		/* r10 is -LAST_ERRNO */
> +0:	cmpld	r3,r11		/* r11 is -MAX_ERRNO */
>  	blt+	1f
>  	andi.	r0,r9,_TIF_NOERROR
>  	bne-	1f