On 06/30/2017 07:52 PM, Michal Hocko wrote: > On Fri 30-06-17 11:59:37, Anshuman Khandual wrote: >> Hello, >> >> execve() system call should support argument length of >> MAX_ARG_STRLEN (PAGE_SIZE * 32). On 64K page size systems, we >> are not able to pass 32 * PAGE_SIZE arguments into the execve() >> system call because of the following reasons. >> >> * struct linux_binprm's vma starts with a size of PAGE_SIZE >> >> vma->vm_end = STACK_TOP_MAX; >> vma->vm_start = vma->vm_end - PAGE_SIZE; >> >> * The VMA expands as much depending upon the argument size. So >> for 32 * PAGE_SIZE argument, it becomes 33 * PAGE_SIZE. >> >> * 33 * PAGE_SIZE with 64K pages fails the following test in >> get_arg_page() function. 33 * PAGE_SIZE is more than 2MB >> (8 MB /4) with 64K page size. >> >> if (size > READ_ONCE(rlim[RLIMIT_STACK].rlim_cur) / 4) >> >> * Right now RLIMIT_STACK is hard coded 8MB which does not take >> PAGE_SIZE into account. >> >> Wondering what should be the solution for this problem ? >> >> * Change the default stack size from 8MB ? > just increase the ulimit if you want to use such a large arguments. >
Yeah that is possible but it does not still offset the fact that the calculation is broken on the page size of 64K. I mean, yeah its not practical to have such a large argument. But the point is whether we would want to support the MAX_ARG_STRLEN semantic for execve system call or not. At present its broken for 64K and I am asking whether we will be willing to revisit the '1/4th of the stack' condition.
