Add the missing pieces in order to enable SECCOMP_FILTER on PowerPC
architectures, and enable this support.
Testing has been pursued using libseccomp with the latest ppc support patches
[1], on Freescale platforms for both ppc and ppc64. ppc64le support is
untested.
[1] https://groups.google.com/forum/#!topic/libseccomp/ktR-bQr1tGw
Bogdan Purcareata (3):
powerpc: Don't force ENOSYS as error on syscall fail
powerpc: Relax secure computing on syscall entry trace
powerpc: Enable HAVE_ARCH_SECCOMP_FILTER
arch/powerpc/Kconfig | 1 +
arch/powerpc/kernel/entry_32.S | 3 ++-
arch/powerpc/kernel/entry_64.S | 2 +-
arch/powerpc/kernel/ptrace.c | 4 +++-
4 files changed, 7 insertions(+), 3 deletions(-)
--
2.1.4
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.
The RFC is this: are there currently any user-space scenarios where it is
required that the system call return ENOSYS as error code on failure, no matter
the circumstances? I don't want to break userspace requirements. I have not
added code to force this error code in situations different than
secure_computing failure, in order to keep overhead at a minimum.
Signed-off-by: Bogdan Purcareata <[email protected]>
---
arch/powerpc/kernel/entry_32.S | 3 ++-
arch/powerpc/kernel/entry_64.S | 2 +-
2 files changed, 3 insertions(+), 2 deletions(-)
diff --git a/arch/powerpc/kernel/entry_32.S b/arch/powerpc/kernel/entry_32.S
index 59848e5..52e48dd 100644
--- a/arch/powerpc/kernel/entry_32.S
+++ b/arch/powerpc/kernel/entry_32.S
@@ -425,7 +425,8 @@ END_FTR_SECTION_IFSET(CPU_FTR_NEED_PAIRED_STWCX)
b 1b
#endif /* CONFIG_44x */
-66: li r3,-ENOSYS
+66:
+# li r3,-ENOSYS
b ret_from_syscall
.globl ret_from_fork
diff --git a/arch/powerpc/kernel/entry_64.S b/arch/powerpc/kernel/entry_64.S
index e6bfe8e..80db02e 100644
--- a/arch/powerpc/kernel/entry_64.S
+++ b/arch/powerpc/kernel/entry_64.S
@@ -269,7 +269,7 @@ syscall_dotrace:
b .Lsyscall_dotrace_cont
syscall_enosys:
- li r3,-ENOSYS
+# li r3,-ENOSYS
b syscall_exit
syscall_exit_work:
--
2.1.4
The secure_computing_strict will just force the kernel to panic on
secure_computing failure. Once SECCOMP_FILTER support is enabled in the kernel,
syscalls can be denied without system failure.
Signed-off-by: Bogdan Purcareata <[email protected]>
---
arch/powerpc/kernel/ptrace.c | 4 +++-
1 file changed, 3 insertions(+), 1 deletion(-)
diff --git a/arch/powerpc/kernel/ptrace.c b/arch/powerpc/kernel/ptrace.c
index 100e01c..5c654ac 100644
--- a/arch/powerpc/kernel/ptrace.c
+++ b/arch/powerpc/kernel/ptrace.c
@@ -1772,7 +1772,9 @@ long do_syscall_trace_enter(struct pt_regs *regs)
user_exit();
- secure_computing_strict(regs->gpr[0]);
+ /* Do the secure computing check first; failures should be fast. */
+ if (secure_computing(regs->gpr[0]) == -1)
+ return -1L;
if (test_thread_flag(TIF_SYSCALL_TRACE) &&
tracehook_report_syscall_entry(regs))
--
2.1.4
Signed-off-by: Bogdan Purcareata <[email protected]>
---
arch/powerpc/Kconfig | 1 +
1 file changed, 1 insertion(+)
diff --git a/arch/powerpc/Kconfig b/arch/powerpc/Kconfig
index a2a168e..72f363e 100644
--- a/arch/powerpc/Kconfig
+++ b/arch/powerpc/Kconfig
@@ -104,6 +104,7 @@ config PPC
select HAVE_EFFICIENT_UNALIGNED_ACCESS if !CPU_LITTLE_ENDIAN
select HAVE_KPROBES
select HAVE_ARCH_KGDB
+ select HAVE_ARCH_SECCOMP_FILTER
select HAVE_KRETPROBES
select HAVE_ARCH_TRACEHOOK
select HAVE_MEMBLOCK
--
2.1.4
Obvious mistake on my behalf to send the patch with lines commented out.
I will fix it in v2.
On 09.02.2015 09:55, 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.
>
> The RFC is this: are there currently any user-space scenarios where it is
> required that the system call return ENOSYS as error code on failure, no matter
> the circumstances? I don't want to break userspace requirements. I have not
> added code to force this error code in situations different than
> secure_computing failure, in order to keep overhead at a minimum.
>
> Signed-off-by: Bogdan Purcareata <[email protected]>
> ---
> arch/powerpc/kernel/entry_32.S | 3 ++-
> arch/powerpc/kernel/entry_64.S | 2 +-
> 2 files changed, 3 insertions(+), 2 deletions(-)
>
> diff --git a/arch/powerpc/kernel/entry_32.S b/arch/powerpc/kernel/entry_32.S
> index 59848e5..52e48dd 100644
> --- a/arch/powerpc/kernel/entry_32.S
> +++ b/arch/powerpc/kernel/entry_32.S
> @@ -425,7 +425,8 @@ END_FTR_SECTION_IFSET(CPU_FTR_NEED_PAIRED_STWCX)
> b 1b
> #endif /* CONFIG_44x */
>
> -66: li r3,-ENOSYS
> +66:
> +# li r3,-ENOSYS
> b ret_from_syscall
>
> .globl ret_from_fork
> diff --git a/arch/powerpc/kernel/entry_64.S b/arch/powerpc/kernel/entry_64.S
> index e6bfe8e..80db02e 100644
> --- a/arch/powerpc/kernel/entry_64.S
> +++ b/arch/powerpc/kernel/entry_64.S
> @@ -269,7 +269,7 @@ syscall_dotrace:
> b .Lsyscall_dotrace_cont
>
> syscall_enosys:
> - li r3,-ENOSYS
> +# li r3,-ENOSYS
> b syscall_exit
>
> syscall_exit_work:
>
On Mon, 2015-02-09 at 07:55 +0000, 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.
>
> The RFC is this: are there currently any user-space scenarios where it is
> required that the system call return ENOSYS as error code on failure, no matter
> the circumstances? I don't want to break userspace requirements. I have not
> added code to force this error code in situations different than
> secure_computing failure, in order to keep overhead at a minimum.
>
> Signed-off-by: Bogdan Purcareata <[email protected]>
> ---
> arch/powerpc/kernel/entry_32.S | 3 ++-
> arch/powerpc/kernel/entry_64.S | 2 +-
> 2 files changed, 3 insertions(+), 2 deletions(-)
>
> diff --git a/arch/powerpc/kernel/entry_32.S b/arch/powerpc/kernel/entry_32.S
> index 59848e5..52e48dd 100644
> --- a/arch/powerpc/kernel/entry_32.S
> +++ b/arch/powerpc/kernel/entry_32.S
> @@ -425,7 +425,8 @@ END_FTR_SECTION_IFSET(CPU_FTR_NEED_PAIRED_STWCX)
> b 1b
> #endif /* CONFIG_44x */
>
> -66: li r3,-ENOSYS
> +66:
> +# li r3,-ENOSYS
> b ret_from_syscall
>
> .globl ret_from_fork
> diff --git a/arch/powerpc/kernel/entry_64.S b/arch/powerpc/kernel/entry_64.S
> index e6bfe8e..80db02e 100644
> --- a/arch/powerpc/kernel/entry_64.S
> +++ b/arch/powerpc/kernel/entry_64.S
> @@ -269,7 +269,7 @@ syscall_dotrace:
> b .Lsyscall_dotrace_cont
>
> syscall_enosys:
> - li r3,-ENOSYS
> +# li r3,-ENOSYS
> b syscall_exit
So what happens if you call this with a syscall number that's out of bounds?
cheers
On 11.02.2015 05:04, Michael Ellerman wrote:
> On Mon, 2015-02-09 at 07:55 +0000, 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.
>>
>> The RFC is this: are there currently any user-space scenarios where it is
>> required that the system call return ENOSYS as error code on failure, no matter
>> the circumstances? I don't want to break userspace requirements. I have not
>> added code to force this error code in situations different than
>> secure_computing failure, in order to keep overhead at a minimum.
>>
>> Signed-off-by: Bogdan Purcareata <[email protected]>
>> ---
>> arch/powerpc/kernel/entry_32.S | 3 ++-
>> arch/powerpc/kernel/entry_64.S | 2 +-
>> 2 files changed, 3 insertions(+), 2 deletions(-)
>>
>> diff --git a/arch/powerpc/kernel/entry_32.S b/arch/powerpc/kernel/entry_32.S
>> index 59848e5..52e48dd 100644
>> --- a/arch/powerpc/kernel/entry_32.S
>> +++ b/arch/powerpc/kernel/entry_32.S
>> @@ -425,7 +425,8 @@ END_FTR_SECTION_IFSET(CPU_FTR_NEED_PAIRED_STWCX)
>> b 1b
>> #endif /* CONFIG_44x */
>>
>> -66: li r3,-ENOSYS
>> +66:
>> +# li r3,-ENOSYS
>> b ret_from_syscall
>>
>> .globl ret_from_fork
>> diff --git a/arch/powerpc/kernel/entry_64.S b/arch/powerpc/kernel/entry_64.S
>> index e6bfe8e..80db02e 100644
>> --- a/arch/powerpc/kernel/entry_64.S
>> +++ b/arch/powerpc/kernel/entry_64.S
>> @@ -269,7 +269,7 @@ syscall_dotrace:
>> b .Lsyscall_dotrace_cont
>>
>> syscall_enosys:
>> - li r3,-ENOSYS
>> +# li r3,-ENOSYS
>> b syscall_exit
>
> So what happens if you call this with a syscall number that's out of bounds?
As far as my current understanding goes, the call will return with -1
with a errno that's undefined (or I've not seen it be defined anywhere).
I've thought more about this, and I guess the best option would be to
move setting -ENOSYS as errno from the syscall entry assembly to
do_syscall_trace_enter (as opposed to eliminating it at all). I was a
little reluctant to do this at first in order to keep overhead to a
minimum, but it's certainly not an option to change behavior if the
syscall number is out of bounds.
v2 to come shortly.
Thanks,
Bogdan P.