On Fri, Nov 27, 2020 at 1:13 PM Andy Lutomirski luto@kernel.org wrote:
On Thu, Nov 26, 2020 at 7:52 AM Jan Kara jack@suse.cz wrote:
Commit converting syscalls taking 64-bit arguments to new scheme of compat handlers omitted converting fanotify_mark(2) which then broke the syscall for 32-bit x86 builds. Add missed conversion. It is somewhat cumbersome since we need to keep the original compat handler for all the other 32-bit archs.
This is stupendously ugly. I'm not really sure how this is supposed to work on any 32-bit arch. I'm also not sure whether we should expect the SYSCALL_DEFINE macros to figure this out by themselves.
It works on 32-bit arches because the compiler implicitly uses consecutive input registers or stack slots for 64-bit arguments, and some arches have alignment requirements that result in hidden padding. x86-32 is different now because parameters are passed in via pt_regs, and the 64-bit value has to explicitly be reassembled from the high and low 32-bit values, just like in the compat case.
I think the simplest way to handle this is add a wrapper in arch/x86/kernel/sys_ia32.c with the other fs syscalls that need 64-bit args. That keeps this mess out of general code.
-- Brian Gerst