On Friday 07 September 2012 11:50 PM, Al Viro wrote: > To architecture maintainers: please, review the current > situation in git.kernel.org/pub/scm/linux/kernel/git/viro/signal #execve2 > and consider sending the corresponding patches for missing architectures. > > What's getting done is unification of sys_execve()/kernel_execve() > into arch-independent code. x86, alpha, arm, s390, um and ppc are already > converted in #execve2. The plan is: > > * provide a new primitive - ret_from_kernel_execve(); it takes two pointers > to struct pt_regs, one being the normal location of pt_regs for a userland > process, another - new pt_regs just filled by do_execve(). It should copy > the latter to the former and bugger off to userland. Called from generic > kernel_execve() implementation (see fs/exec.c in #execve2). It almost always > has to be done in assembler - normally it does equivalent of something > along the lines of > memmove(normal, new, sizeof(struct pt_regs)) > sp = normal, or whatever is needed to get a valid stack > frame (e.g. on s390 there's ->back_chain that needs to be set to > NULL) > set other registers ret_from_sys_call expects to be set (e.g. > i386 syscall entry has current_thread_info() value cached in %ebp and > since it's a callee-saved register there, ret_from_sys_call expects to > find that value still in %ebp, so we need to set it); basically, check > what has to be set in ret_from_fork - it tends to jump to the same place. > goto ret_from_sys_call, or whatever the equivalent is called on > particular architecture. > * define __ARCH_WANT_KERNEL_EXECVE in unistd.h, remove your old kernel_execve() > * pull whatever work you'd been doing *after* do_execve() call in your > sys_execve() (most of the architectures don't do anything after that anyway) > into start_thread(); that's the point of no return for execve(2) and if we > get there, we'll either succeed or get killed with SIGKILL. The same goes > for compat variant of execve(), with s/start_thread/compat_start_thread/. > * define __ARCH_WANT_SYS_EXECVE in unistd.h, kill your sys_execve() and > compat counterpart (if any). > * if there's a better way to calculate task_pt_regs(current), you can provide > it in your ptrace.h - macro should be called current_pt_regs(); it's optional. > > Status: x86, arm, um, s390 - converted, tested, seem to work. alpha > and ppc - need testing. The rest - hadn't touched yet. unicore32 and > blackfin should be trivial to convert (they are doing kernel_execve() in > that manner already). Other may be more or less tricky - depends on how > gnarly their return from syscall path happens to be. I'll do what I can > and test what I can (some on emulators, some on real hardware), but for quite > a few architectures I've no way to test. Nor am I fond of sniffing dozens > of variants of assembler glue, to put it mildly. > > Patches and/or help with testing setups would be very welcome. > Hi Al, It must be noted that despite having seemingly independent __ARCH_WANT_(KERNEL|SYS)_EXECVE, arches which have a kernel syscall trap based kernel_execve(), e.g. MIPS, can't implement __ARCH_WANT_SYS_EXECVE alone - they need to first convert to __ARCH_WANT_KERNEL_EXECVE as well (although it probably doesn't make sense for anyone to just implement one - but in terms of staging - having only one, breaks stuff IMHO). The reason being, for non converted kernel_execve(), the call-stack leading to sys_execve (e.g. init_post -> run_init_process -> kernel_execve ->..) would cause the pt_regs layout to be slightly offsetted from bottom of stack - not exactly where current_pt_regs()/task_pt_regs(current) would point to in general. Thus on return path the update by start_thread() won't be visible to asm glue at expected location. I ran into this myself - when doing the execve switch for ARC Linux port (currently being "pre-reviewed" by tglx before submission to lkml). -Vineet -- To unsubscribe from this list: send the line "unsubscribe linux-arch" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
