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| author | Chris Zankel <chris@zankel.net> | 2012-10-24 13:15:21 -0700 |
|---|---|---|
| committer | Chris Zankel <chris@zankel.net> | 2012-10-25 14:53:36 -0700 |
| commit | 6ebe7da25b7879194fdb5c43ea67b383dd9014d6 (patch) | |
| tree | 078aca917e5fe9db80af42298210684d250f98bf /arch/xtensa | |
| parent | cddfcbcd05851a3b720055d40fc61c63ea1c2bd1 (diff) | |
| download | lwn-6ebe7da25b7879194fdb5c43ea67b383dd9014d6.tar.gz lwn-6ebe7da25b7879194fdb5c43ea67b383dd9014d6.zip | |
xtensa: reset windowbase/windowstart when cloning the VM
When we copy a user thread with CLONE_VM, we also have to reset
windowbase and windowstart to start a pristine stack frame. Otherwise,
overflows can happen using the address 0 as the stack pointer.
Also add a special case for vfork, which continues on the
parent stack until it calls execve. Because this could be a call8, we
need to spill the stack pointer of the previus frame (if still 'live' in
the register file).
Signed-off-by: Chris Zankel <chris@zankel.net>
Diffstat (limited to 'arch/xtensa')
| -rw-r--r-- | arch/xtensa/kernel/process.c | 26 |
1 files changed, 25 insertions, 1 deletions
diff --git a/arch/xtensa/kernel/process.c b/arch/xtensa/kernel/process.c index 1908f6642d31..341c151af919 100644 --- a/arch/xtensa/kernel/process.c +++ b/arch/xtensa/kernel/process.c @@ -220,8 +220,32 @@ int copy_thread(unsigned long clone_flags, unsigned long usp, if (user_mode(regs)) { childregs->areg[1] = usp; + + /* When sharing memory with the parent thread, the child + usually starts on a pristine stack, so we have to reset + windowbase, windowstart and wmask. + (Note that such a new thread is required to always create + an initial call4 frame) + The exception is vfork, where the new thread continues to + run on the parent's stack until it calls execve. This could + be a call8 or call12, which requires a legal stack frame + of the previous caller for the overflow handlers to work. + (Note that it's always legal to overflow live registers). + In this case, ensure to spill at least the stack pointer + of that frame. */ + if (clone_flags & CLONE_VM) { - childregs->wmask = 1; /* can't share live windows */ + /* check that caller window is live and same stack */ + int len = childregs->wmask & ~0xf; + if (regs->areg[1] == usp && len != 0) { + int callinc = (regs->areg[0] >> 30) & 3; + int caller_ars = XCHAL_NUM_AREGS - callinc * 4; + put_user(regs->areg[caller_ars+1], + (unsigned __user*)(usp - 12)); + } + childregs->wmask = 1; + childregs->windowstart = 1; + childregs->windowbase = 0; } else { int len = childregs->wmask & ~0xf; memcpy(&childregs->areg[XCHAL_NUM_AREGS - len/4], |