On Wed, Aug 09, 2023 at 04:34:38PM +0100, Mark Brown wrote: > On Wed, Aug 09, 2023 at 03:24:14PM +0100, Catalin Marinas wrote: > > On Mon, Aug 07, 2023 at 11:00:08PM +0100, Mark Brown wrote: > > > +* When set PR_SHADOW_STACK_ENABLE flag allocates a Guarded Control Stack for > > > > The 'for' at the end of the line above is not needed. > > > > > + and enables GCS for the thread, enabling the functionality controlled by > > I find it a little clearer that it's a per thread stack here but sure. If it reads better for you, feel free to keep it as is. > > > +3. Allocation of Guarded Control Stacks > > > +---------------------------------------- > > > > +* When GCS is enabled for a thread a new Guarded Control Stack will be > > > + allocated for it of size RLIMIT_STACK / 2 or 2 gigabytes, whichever is > > > + smaller. > > > Is this number based on the fact that a function call would only push > > the LR to GCS while standard function prologue pushes at least two > > registers? > > It's actually based on bitrot that I'd initially chosen a smaller value > since it's likely that functions will push at least something as you > suggest, the patches now just use RLIMIT_STACK. I'll fix. A related question - it may have been discussed intensively on the x86 thread (I may read it sometime) - why not have the libc map the shadow stack and pass the pointer/size to clone3()? It saves us from having to guess what the right size we'd need. struct clone_args is extensible. (I plan to get back next week to this series, I'll need to read a bit more on the spec) -- Catalin
