2010/11/22 Jakub Kiciński <moor...@wp.pl> > Hi, > > Dnia 19-11-2010 o 06:17:53 Venkatram Tummala <venkatram...@gmail.com> > napisał(a): > > 2010/11/18 Parmenides <mobile.parmeni...@gmail.com> >> >> 2. For the kernel code, is it feasible to the use the user stack? Why >>> do we bother to switch to the kernel stack? >>> >>> The answer is Yes, you could. But it would be pretty messy & >> inconvenient. >> We just don't do it in the linux kernel atleast on x86. Kernel Data >> Segment >> & User Data Segment is different. I guess you could just map the user >> space >> stack in the kernel address space too & use it. Using two seperate stacks >> is >> just more efficient & convenient. >> > > Wouldn't it be a security bug to use the same stack for both? Kernel > function's parameters and auto variables would be still sitting above (well, > in x86 under ;) stack pointer. Not sure though if attacker could find > anything interesting there... > I don't think so. Kernel function's parameters & auto variables on the stack only live until the lifetime of the procedure. If we were using just one stack for both user & kernel, when we make a switch (1) user -> kernel & then (2) kernel->user, the stack would be in the state it was before (1). Its a stack. If procedure A calls Procedure B in single shared address space, they share the stack. When procedure B returns, there is nothing to poke around for Procedure A about Procedure B on the stack.
Venkatram Tummala > > Regards, > moorray >
