Subject: Re: [PATCH v3 1/3] powerpc: Don't force ENOSYS as error on syscall fail

From: Mike Strosaker <[email-masked]>
Date: Tue, 17 Feb 2015 21:01:19 -0600

This patch failed to build using pseries_le_defconfig.  With the change 
noted below in entry_64.S, the build succeeded and seccomp mode 2 worked 
correctly.

Best,
Mike Strosaker

On 02/13/2015 02:22 AM, Bogdan Purcareata wrote:
> In certain scenarios - e.g. seccomp filtering with ERRNO as default action -
> the system call fails for other reasons than the syscall not being available.
> The seccomp filter can be configured to store a user-defined error code on
> return from a blacklisted syscall. Don't always set ENOSYS on
> do_syscall_trace_enter failure.
>
> Delegate setting ENOSYS in case of failure, where appropriate, to
> do_syscall_trace_enter.
>
> v3:
> - keep setting ENOSYS in the syscall entry assembly for scenarios without
>    syscall tracing
>
> v2:
> - move setting ENOSYS as errno from the syscall entry assembly to
>    do_syscall_trace_enter, only in the specific case
>
> Signed-off-by: Bogdan Purcareata <[email-masked]>
> ---
>   arch/powerpc/kernel/entry_32.S | 7 ++++++-
>   arch/powerpc/kernel/entry_64.S | 5 +++--
>   arch/powerpc/kernel/ptrace.c   | 4 +++-
>   3 files changed, 12 insertions(+), 4 deletions(-)
>
> diff --git a/arch/powerpc/kernel/entry_32.S b/arch/powerpc/kernel/entry_32.S
> index 46fc0f4..b2f88cd 100644
> --- a/arch/powerpc/kernel/entry_32.S
> +++ b/arch/powerpc/kernel/entry_32.S
> @@ -333,12 +333,12 @@ _GLOBAL(DoSyscall)
>   	lwz	r11,TI_FLAGS(r10)
>   	andi.	r11,r11,_TIF_SYSCALL_DOTRACE
>   	bne-	syscall_dotrace
> -syscall_dotrace_cont:
>   	cmplwi	0,r0,NR_syscalls
>   	lis	r10,sys_call_table@h
>   	ori	r10,r10,sys_call_table@l
>   	slwi	r0,r0,2
>   	bge-	66f
> +syscall_dotrace_cont:
>   	lwzx	r10,r10,r0	/* Fetch system call handler [ptr] */
>   	mtlr	r10
>   	addi	r9,r1,STACK_FRAME_OVERHEAD
> @@ -457,6 +457,11 @@ syscall_dotrace:
>   	lwz	r7,GPR7(r1)
>   	lwz	r8,GPR8(r1)
>   	REST_NVGPRS(r1)
> +	cmplwi	0,r0,NR_syscalls
> +	lis	r10,sys_call_table@h
> +	ori	r10,r10,sys_call_table@l
> +	slwi	r0,r0,2
> +	bge-	ret_from_syscall
>   	b	syscall_dotrace_cont
>
>   syscall_exit_work:
> diff --git a/arch/powerpc/kernel/entry_64.S b/arch/powerpc/kernel/entry_64.S
> index d180caf2..0d22fa8 100644
> --- a/arch/powerpc/kernel/entry_64.S
> +++ b/arch/powerpc/kernel/entry_64.S
> @@ -144,7 +144,6 @@ END_FW_FTR_SECTION_IFSET(FW_FEATURE_SPLPAR)
>   	ld	r10,TI_FLAGS(r11)
>   	andi.	r11,r10,_TIF_SYSCALL_DOTRACE
>   	bne	syscall_dotrace
> -.Lsyscall_dotrace_cont:
>   	cmpldi	0,r0,NR_syscalls
>   	bge-	syscall_enosys
>
> @@ -253,7 +252,9 @@ syscall_dotrace:
>   	addi	r9,r1,STACK_FRAME_OVERHEAD
>   	CURRENT_THREAD_INFO(r10, r1)
>   	ld	r10,TI_FLAGS(r10)
> -	b	.Lsyscall_dotrace_cont
> +	cmpldi	0,r0,NR_syscalls
> +	bge-	syscall_exit

Shouldn't this be .Lsyscall_exit?

> +	b	system_call
>
>   syscall_enosys:
>   	li	r3,-ENOSYS
> diff --git a/arch/powerpc/kernel/ptrace.c b/arch/powerpc/kernel/ptrace.c
> index f21897b..2edae06 100644
> --- a/arch/powerpc/kernel/ptrace.c
> +++ b/arch/powerpc/kernel/ptrace.c
> @@ -1775,13 +1775,15 @@ long do_syscall_trace_enter(struct pt_regs *regs)
>   	secure_computing_strict(regs->gpr[0]);
>
>   	if (test_thread_flag(TIF_SYSCALL_TRACE) &&
> -	    tracehook_report_syscall_entry(regs))
> +	    tracehook_report_syscall_entry(regs)) {
>   		/*
>   		 * Tracing decided this syscall should not happen.
>   		 * We'll return a bogus call number to get an ENOSYS
>   		 * error, but leave the original number in regs->gpr[0].
>   		 */
>   		ret = -1L;
> +		syscall_set_return_value(current, regs, ENOSYS, 0);
> +	}
>
>   	if (unlikely(test_thread_flag(TIF_SYSCALL_TRACEPOINT)))
>   		trace_sys_enter(regs, regs->gpr[0]);
>