Re: [PATCH v5 4/6] mm: simplify compat numa syscalls

On Tue, Jul 27, 2021 at 07:40:05PM +0200, Arnd Bergmann wrote:

On Tue, Jul 27, 2021 at 7:27 PM Heiko Carstens [off-list ref] wrote:

quoted

quoted

+static int get_bitmap(unsigned long *mask, const unsigned long __user *nmask,
+                   unsigned long maxnode)
+{
+     unsigned long nlongs = BITS_TO_LONGS(maxnode);
+     int ret;
+
+     if (in_compat_syscall())
+             ret = compat_get_bitmap(mask,
+                                     (const compat_ulong_t __user *)nmask,
+                                     maxnode);

compat_ptr() conversion for e.g. nmask is missing with the next patch
which removes the compat system calls.
Is that intended or am I missing something?

I don't think it's needed here, since the pointer comes from the system
call argument, which has the compat_ptr() conversion applied in
arch/s390/include/asm/syscall_wrapper.h, not from a compat_uptr_t
that gets passed indirectly. The compat_get_bitmap() conversion
is only needed for byte order adjustment, not for converting pointers.

It's also possible that I'm the one who's missing something.

What I was trying to say: this patch on its own is ok. However with
the next patch you remove the compat system calls and map the regular
system calls instead.

That is:

-COMPAT_SYSCALL_DEFINE6(mbind, compat_ulong_t, start, compat_ulong_t, len,
-		       compat_ulong_t, mode, compat_ulong_t __user *, nmask,
-		       compat_ulong_t, maxnode, compat_ulong_t, flags)
-{
-	return kernel_mbind(start, len, mode, (unsigned long __user *)nmask,
-			    maxnode, flags);
-}

and this:

-268  common	mbind			sys_mbind			compat_sys_mbind
-269  common	get_mempolicy		sys_get_mempolicy		compat_sys_get_mempolicy
-270  common	set_mempolicy		sys_set_mempolicy		compat_sys_set_mempolicy
+268  common	mbind			sys_mbind			sys_mbind
+269  common	get_mempolicy		sys_get_mempolicy		sys_get_mempolicy
+270  common	set_mempolicy		sys_set_mempolicy		sys_set_mempolicy

would remove compat_ptr() conversion from nmask above if I'm not mistaken.