On Tue, Dec 01, 2020 at 09:34:32AM -0800, Andy Lutomirski wrote: > On Tue, Dec 1, 2020 at 9:23 AM Andy Lutomirski <luto@xxxxxxxxxx> wrote: > > On Mon, Nov 30, 2020 at 2:31 PM Brian Gerst <brgerst@xxxxxxxxx> wrote: > > > Commit 121b32a58a3a converted native x86-32 which take 64-bit arguments to > > > use the compat handlers to allow conversion to passing args via pt_regs. > > > sys_fanotify_mark() was however missed, as it has a general compat handler. > > > Add a config option that will use the syscall wrapper that takes the split > > > args for native 32-bit. > > > > > > Reported-by: Paweł Jasiak <pawel@xxxxxxxxxx> > > > Fixes: 121b32a58a3a ("x86/entry/32: Use IA32-specific wrappers for syscalls taking 64-bit arguments") > > > Signed-off-by: Brian Gerst <brgerst@xxxxxxxxx> > > > --- > > > arch/Kconfig | 6 ++++++ > > > arch/x86/Kconfig | 1 + > > > fs/notify/fanotify/fanotify_user.c | 17 +++++++---------- > > > include/linux/syscalls.h | 24 ++++++++++++++++++++++++ > > > 4 files changed, 38 insertions(+), 10 deletions(-) > > > > > > diff --git a/arch/Kconfig b/arch/Kconfig > > > index 090ef3566c56..452cc127c285 100644 > > > --- a/arch/Kconfig > > > +++ b/arch/Kconfig > > > @@ -1045,6 +1045,12 @@ config HAVE_STATIC_CALL_INLINE > > > bool > > > depends on HAVE_STATIC_CALL > > > > > > +config ARCH_SPLIT_ARG64 > > > + bool > > > + help > > > + If a 32-bit architecture requires 64-bit arguments to be split into > > > + pairs of 32-bit arguemtns, select this option. > > > > You misspelled arguments. You might also want to clarify that, for > > 64-bit arches, this means that compat syscalls split their arguments. > > No, that's backwards. Maybe it should be depends !64BIT instead. > > But I'm really quite confused about something: what's special about > x86 here? Are there really Linux arches (compat or 32-bit native) > that *don't* split arguments like this? Sure, some arches probably > work the same way that x86 used to in which the compiler did the > splitting by magic for us, but that was always a bit of a kludge. On arm32 we rely on the compiler splitting a 64-bit argument in two consecutive registers. But I wouldn't say it's a kludge (well, mostly) as that's part of the arm procedure calling standard. Currently arm32 doesn't pass the syscall arguments through a read from pt_regs, so all is handled transparently. On arm64 compat, we need to re-assemble the arguments with some wrappers explicitly (arch/arm64/kernel/sys32.c) or call the generic wrapper like in the compat_sys_fanotify_mark() case. > Could this change maybe be made unconditional? I think it's fine in this particular case. I don't think it's valid in general because of the arm (and maybe others) requirement that the first register of a 64-bit argument is an even number (IIRC, Russell should know better). If the u64 mask was an argument before or after the current position, the compiler would have introduced a pad register but not if the arg is split in two u32. -- Catalin