On Fri, 2023-02-24 at 13:22 +0100, Borislav Petkov wrote: > On Sat, Feb 18, 2023 at 01:14:21PM -0800, Rick Edgecombe wrote: > > Do not support IA32 emulation or x32. > > Because? Simplicity? > > No one cares about 32-bit? Yea a little of both. Originally shadow stack 32 bit emulation was supported for 64 bit kernels, but then Andy Lutomirski asked for the signal ABI to flexible enough to support alt shadow stacks in the future. This involved stuffing things on the shadow stack that didn't work well for 32 bit. Resolving this wasn't exhaustively explored, but there weren't any obvious things that jumped out. Then there was the question of how much 32 bit CET apps running on 64 bit kernels would get used. Since shadow stack needs a re-compile this would only be for newly build 32 bit binaries, not old legacy binaries that seems to be the thing often using legacy emulation. So it was kind of not expected to be used much or at all, so any kind of complications tipped the scales toward dropping it. PeterZ brought up WINE running 32 bit Windows apps, but apparently Windows doesn't support 32 bit CET either. And then there is that we can always add it later if a big use shows up. I'll add a little more info in the commit log about this.
