On 03/18/2018 07:13 PM, Andy Lutomirski wrote:
On Sun, Mar 18, 2018 at 6:47 AM, Dominik Brodowski
<linux@xxxxxxxxxxxxxxxxxxxx> wrote:
On Fri, Mar 16, 2018 at 03:55:04PM -0700, Howard McLauchlan wrote:
On 03/13/2018 04:56 PM, Andy Lutomirski wrote:
On Tue, Mar 13, 2018 at 11:16 PM, Howard McLauchlan <hmclauchlan@xxxxxx> wrote:
Error injection is a useful mechanism to fail arbitrary kernel
functions. However, it is often hard to guarantee an error propagates
appropriately to user space programs. By injecting into syscalls, we can
return arbitrary values to user space directly; this increases
flexibility and robustness in testing, allowing us to test user space
error paths effectively.
Temporary NAK IMO. Specifically:
diff --git a/include/linux/syscalls.h b/include/linux/syscalls.h
index a78186d826d7..e8c6d63ace78 100644
--- a/include/linux/syscalls.h
+++ b/include/linux/syscalls.h
@@ -191,6 +191,8 @@ static inline int is_syscall_trace_event(struct trace_event_call *tp_event)
#define SYSCALL_DEFINE0(sname) \
SYSCALL_METADATA(_##sname, 0); \
+ asmlinkage long sys_##sname(void); \
+ ALLOW_ERROR_INJECTION(sys_##sname, ERRNO); \
sys_xyz() is not just the syscall itself; it's also a helper that's
used for entirely silly reasons by various bits of kernel code for
quite a few syscalls. Fortunately, Dominik has patches to fix that,
and Linus is even considering pulling them for 4.16. This patch will
most likely conflict with the final result of Dominik's series.
Can you and Dominik coordinate a bit to get this patch or its
equivalent landed on top of Dominik's work? It might make sense for
Dominik to just add this patch to his series so it can land with the
rest of it. Dominik, Ingo, what do you think?
--Andy
Dominik,
This patch applies cleanly on top of your patch series. Is there anything you'd need from me to get this in on top of your work?
Howard,
would this form part of the kernel<->userspace interface and therefore needs
to be kept stable? If so, this patch should wait until the arch-specific
syscall calling convention is agreed upon.
Moreover, the patches I sent out already do not cover all syscalls yet.
Until all in-kernel users of sys_*() are gone (or at least outside arch/),
I'd prefer to postpone this patch.
I was assuming that this ALLOW_ERROR_INJECTION thing is *not*
considered stable ABI. We should be free to change the way that the
syscall entry code calls syscalls whenever we like.
If you want a stable syscall error injection mechanism, make it work
like seccomp instead, please.
This is not supposed to be considered stable. It's for debug purposes only and
would normally be configured off.
Howard
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