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SubjectRe: [PATCH v3 1/3] powerpc: Don't force ENOSYS as error on syscall fail
On 18.02.2015 05:01, Mike Strosaker wrote:
> 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 <bogdan.purcareata@freescale.com>
>> ---
>> 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?

Thanks for testing and spotting this! The kernel I tested with didn't
have syscall_exit converted to a local label (commit
4c3b21686111e0ac6018469dacbc5549f9915cf8).

Will resend with this change.

Bogdan P.

>> + 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]);
>>
>


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