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* [RFC] status of execve() work - per-architecture patches solicited
@ 2012-09-07 18:20 Al Viro
  2012-09-07 18:22 ` Al Viro
                   ` (4 more replies)
  0 siblings, 5 replies; 22+ messages in thread
From: Al Viro @ 2012-09-07 18:20 UTC (permalink / raw)
  To: linux-arch; +Cc: linux-kernel

	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.

^ permalink raw reply	[flat|nested] 22+ messages in thread
end of thread, other threads:[~2012-09-24 10:59 UTC | newest]

Thread overview: 22+ messages (download: mbox.gz / follow: Atom feed)
-- links below jump to the message on this page --
2012-09-07 18:20 [RFC] status of execve() work - per-architecture patches solicited Al Viro
2012-09-07 18:22 ` Al Viro
2012-09-10 13:40 ` Greg Ungerer
2012-09-10 16:49   ` Al Viro
2012-09-11  3:39     ` Greg Ungerer
2012-09-13 13:27     ` Greg Ungerer
2012-09-10 22:20 ` Mark Salter
2012-09-10 22:20   ` [PATCH 1/2] c6x: implement ret_from_kernel_execve() and switch to generic kernel_execve() Mark Salter
2012-09-10 22:20   ` [PATCH 2/2] c6x: switch to generic sys_execve() Mark Salter
2012-09-17  3:26   ` [RFC] status of execve() work - per-architecture patches solicited Al Viro
2012-09-21 16:26     ` Mark Salter
2012-09-21 16:26       ` [PATCH 1/3] c6x: add ret_from_kernel_thread(), simplify kernel_thread() Mark Salter
2012-09-21 16:26       ` [PATCH 2/3] c6x: switch to generic kernel_execve Mark Salter
2012-09-21 16:26       ` [PATCH 3/3] c6x: switch to generic sys_execve Mark Salter
2012-09-21 18:39       ` [RFC] status of execve() work - per-architecture patches solicited Al Viro
2012-09-22 11:16         ` Greg Ungerer
2012-09-23  0:46           ` Al Viro
2012-09-24 10:59             ` Vineet Gupta
2012-09-17  9:29 ` Michal Simek
2012-09-17 22:57   ` Al Viro
2012-09-19 12:20 ` Vineet Gupta
2012-09-19 13:32   ` Al Viro

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