On Tue, May 10, 2016 at 9:30 AM, Cyrill Gorcunov <[email protected]> wrote: > On Tue, May 10, 2016 at 09:07:49AM -0700, Andy Lutomirski wrote: >> Hi all- >> >> I'm trying to get rid of x86's dynamic TASK_SIZE and just redefine it >> to TASK_SIZE_MAX. So far, these are the TASK_SIZE users that actually >> seem to care about the task in question: >> >> get_unmapped_area. This is used by mmap, mremap, exec, uprobe XOL, >> and maybe some other things. >> >> - mmap, mremap, etc: IMO this should check in_compat_syscall, not >> TIF_ADDR32. If a 64-bit task does an explicit 32-bit mmap (using int >> $0x80, for example), it should get a 32-bit address back. >> >> - xol_add_vma: This one is weird: uprobes really is doing something >> behind the task's back, and the addresses need to be consistent with >> the address width. I'm not quite sure what to do here. >> >> - exec. This wants to set up mappings that are appropriate for the new >> task. >> >> My inclination would be add a new 'limit' parameter to all the >> get_unmapped_area variants and possible to vm_brk and friends and to >> thus push the decision into the callers. For the syscalls, we could >> add: >> >> static inline unsigned long this_syscall_addr_limit(void) { return >> TASK_SIZE; } >> >> and override it on x86. >> >> I'm not super excited to write that patch, though... > > Andy, could you please highlight what's wrong with TASK_SIZE helper > in first place? The idea behind is to clean up the code or there > some real problem?
It's annoying and ugly. It also makes the idea of doing 32-bit CRIU restore by starting in 64-bit mode and switching to 32-bit more complicated because it requires switching TASK_SIZE. --Andy -- Andy Lutomirski AMA Capital Management, LLC
