On Sun, Apr 08, 2018 at 10:35:50AM +0200, Ingo Molnar wrote:
> - _____sys_waitid() # ridiculous number of underscores?
> - __sys_waitid() # too generic sounding?
... and we'd need to rename internal helpers in net/
> - __inline_sys_waitid() # too long?
sounds acceptable, though a bit long (especially for the compat case, though
it doesn't really matter in the case of
__inline_compat_sys_sched_rr_get_interval)
> One more fundamental question: why do we have the __do_sys_waitid() and
> __inline_sys_waitid() distinction - aren't the function call signatures the same
> with no conversion done?
>
> I.e. couldn't we just do a single, static __do_sys_waitid(), where the compiler
> would decide to what extent inlining is justified? This would allow the compiler
> to inline all the intermediate code into the stubs themselves.
>
> Or is this a side effect of the error injection feature, which needs to add extra
> logic at this intermediate level? That too should be able to use the
> __do_sys_waitid() variant though.
Error injection is unrelated. It seems to be for three reasons, if I read
the code (include/linux/syscalls.h) correctly:
asmlinkage long __do_sys##name(__MAP(x,__SC_LONG,__VA_ARGS__))
1) This takes arguments of type long (to protect against CVE-2009-0029);
see https://lwn.net/Articles/604287/ : "Digging into the history of
this, it turns out that the long version ensures that 32-bit values
are correctly sign-extended for some 64-bit kernel platforms,
preventing a historical vulnerability."
{
long ret = __in_sys##name(__MAP(x,__SC_CAST,__VA_ARGS__));
__MAP(x,__SC_TEST,__VA_ARGS__);
2) We can add testing whether one of the arguments is longer than long.
__PROTECT(x, ret,__MAP(x,__SC_ARGS,__VA_ARGS__));
3) This adds asmlinkage_protect() on m68k, but seems to be a no-op on other
architectures.
While reasons 1 and 3 seem irrelevant on x86, I'd like to keep the code
close to the generic one -- and reason 2 is valid in and by itself. So I'd
recommend keeping the __inline_sys / __do_sys indirection.
> Is UML unaffected by these renames?
UML is only affected by patch 3/3, but kept happy by the patch to
entry/syscalls/syscalltbl.sh.
On a somewhat related note: I'll try to prepare a patch this evening which
lets us build just the __ia32_sys and __x32_compat_sys stubs we actually
need. We have that information already in entry/syscalls/syscall_{32,64}.tbl,
it just needs to be extracted into another header file (in the form of
#define NEED_IA32_sys_xyzzz 1
) and then tested within the stubs. After some randconfig testing, this
might be worthwile to add on top of the patches already in tip-asm and the
three renaming patches currently under discussion.
Thanks,
Dominik
