From: Chris Zankel <chris@xxxxxxxxxx>
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@xxxxxxxxxx>
---
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 1908f66..341c151 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],
--
1.7.7.6
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