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)