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Date: Wed, 11 Feb 2015 09:59:25 +0200 From: Purcareata Bogdan <b43198@...escale.com> To: Michael Ellerman <mpe@...erman.id.au>, Bogdan Purcareata <bogdan.purcareata@...escale.com> CC: <benh@...nel.crashing.org>, <paulus@...ba.org>, <linuxppc-dev@...ts.ozlabs.org>, <pmoore@...hat.com>, <linux-kernel@...r.kernel.org>, <strosake@...ux.vnet.ibm.com> Subject: Re: [RFC][PATCH 1/3] powerpc: Don't force ENOSYS as error on syscall fail 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 <bogdan.purcareata@...escale.com> >> --- >> 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. -- To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majordomo@...r.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/
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