Kevin, Joey, On Wed, Oct 09, 2024 at 03:43:01PM +0100, Will Deacon wrote: > On Tue, Sep 24, 2024 at 01:27:58PM +0200, Kevin Brodsky wrote: > > On 22/08/2024 17:11, Joey Gouly wrote: > > > @@ -1178,6 +1237,9 @@ static void setup_return(struct pt_regs *regs, struct k_sigaction *ka, > > > sme_smstop(); > > > } > > > > > > + if (system_supports_poe()) > > > + write_sysreg_s(POR_EL0_INIT, SYS_POR_EL0); > > > > At the point where setup_return() is called, the signal frame has > > already been written to the user stack. In other words, we write to the > > user stack first, and then reset POR_EL0. This may be problematic, > > especially if we are using the alternate signal stack, which the > > interrupted POR_EL0 may not grant access to. In that situation uaccess > > will fail and we'll end up with a SIGSEGV. > > > > This issue has already been discussed on the x86 side, and as it happens > > patches to reset PKRU early [1] have just landed. I don't think this is > > a blocker for getting this series landed, but we should try and align > > with x86. If there's no objection, I'm planning to work on a counterpart > > to the x86 series (resetting POR_EL0 early during signal delivery). > > Did you get a chance to work on that? It would be great to land the > fixes for 6.12, if possible, so that the first kernel release with POE > support doesn't land with known issues. Looking a little more at this, I think we have quite a weird behaviour on arm64 as it stands. It looks like we rely on the signal frame to hold the original POR_EL0 so, if for some reason we fail to allocate space for the POR context, I think we'll return back from the signal with POR_EL0_INIT. That seems bad? Will
