The 11/16/2023 12:33, Mark Brown wrote: > On Thu, Nov 16, 2023 at 10:32:06AM +0000, Szabolcs.Nagy@xxxxxxx wrote: > > The 11/16/2023 00:52, Edgecombe, Rick P wrote: > > > On Wed, 2023-11-15 at 18:43 +0000, Mark Brown wrote: > > > while CLONE_VFORK allows the child to use the parent shadow > > stack (parent and child cannot execute at the same time and > > the child wont return to frames created by the parent), we > > want to enable precise size accounting of the shadow stack > > so requesting a new shadow stack should work if new stack > > is specified. > > > but stack==0 can force shadow_stack_size==0. > > > i guess the tricky case is stack!=0 && shadow_stack_size==0: > > the user may want a new shadow stack with default size logic, > > or (with !CLONE_VM || CLONE_VFORK) wants to use the existing > > shadow stack from the parent. > > If shadow_stack_size is 0 then we're into clone() behaviour and doing > the default/implicit handling which is to do exactly what the above > describes. sounds good. > > > What is the case for stack=sp bit of the logic? > > > iirc it is not documented in the clone man page what stack=0 > > means and of course you don't want sp==0 in the vfork child > > so some targets sets stack to sp in vfork, others set it 0 > > and expect the kernel to do the right thing. > > The manual page explicitly says that not specifying a stack means to use > the same stack area as the parent. not for clone. clone3 yes. > > this likely does not apply to clone3 where the size has to be > > specified so maybe stack==sp does not need special treatment. > > You'd have to be jumping through hoops to manage to get the same stack > pointer while explicitly specifying a stack with clone3() on > architectures where the stack grows down. I'm not sure there's a > reasonable use case. ok makes sense. IMPORTANT NOTICE: The contents of this email and any attachments are confidential and may also be privileged. If you are not the intended recipient, please notify the sender immediately and do not disclose the contents to any other person, use it for any purpose, or store or copy the information in any medium. Thank you.
