On Thu, Apr 25, 2019 at 10:07:25PM +0200, Ingo Molnar wrote: > > But yes, your above diff for "has NX" is roughly correct. I'll walk > > through each piece I'm thinking about. Here is the current state: > > > > CPU: | lacks NX* | has NX, ia32 | has NX, x86_64 | > > ELF: | | | | > > missing GNU_STACK | exec-all | exec-all | exec-all | > > GNU_STACK == RWX | exec-all | exec-all | exec-all | > > GNU_STACK == RW | exec-none | exec-none | exec-none | > > > > *this column has no architecture effect: NX markings are ignored by > > hardware, but may have behavioral effects when "wants X" collides with > > "cannot be X" constraints in memory permission flags, as in [1]. > > So [1] appears to be device driver mapping a BAR that isn't intended to > be excutable: > > https://lore.kernel.org/netdev/20190418055759.GA3155@xxxxxxxxxxxx/ > > and the question is, do we reject this at the device driver mmap() level > already, right? No, we wanted to reject it at the driver mmap() level, but if an executable is marked with GNU_STACK=RWX then the core mm code always calls the driver with VM_EXEC (even though the mmap isn't a stack) and the driver becomes incompatible with userspace using GNU_STACK=RWX (ie some Fortran programs, apparently) > I suspect the best behavior is to reject as early as possible, so I agree > with your change here - even though !NX systems tend to become less and > less relevant these days. I suggested the idea of adding a flag in either the struct file or the file_operations flag that says mmap is never to be executable for this file with the idea that most/all cdev users would set it. Does that seem reasonable? Jason
