From 3f1642e4bc86c6e7febc6b2dd2b83ad48c5ee201 Mon Sep 17 00:00:00 2001 From: Jamie Liu Date: Fri, 8 Oct 2021 18:00:36 -0700 Subject: Remove ring0 floating point save/load functions on amd64. ring0.Save/LoadFloatingPoint() are only usable if the caller can ensure that Go will not clobber floating point registers before/after calling them respectively. Due to regabig in Go 1.17, this is no longer the case; regabig (among other things) maintains a zeroed XMM15 during ABIInternal execution, including by zeroing it after ABI0-to-ABIInternal transitions. In ring0.sysenter/exception, this happens in ring0.kernelSyscall/kernelException.abi0 respectively; in ring0.CPU.SwitchToUser, this happens after returning from ring0.sysret/iret.abi0. Delete these functions and do floating point save/load in assembly. While arm64 doesn't appear to be immediately affected (so this CL permits us to resume usage of Go 1.17), its use of Save/LoadFloatingPoint() still seems to be incorrect for the same fundamental reason (Go code can't sanely assume what registers the Go compiler will or won't use) and should be fixed eventually. PiperOrigin-RevId: 401895658 --- pkg/ring0/entry_amd64.go | 5 ----- 1 file changed, 5 deletions(-) (limited to 'pkg/ring0/entry_amd64.go') diff --git a/pkg/ring0/entry_amd64.go b/pkg/ring0/entry_amd64.go index afd646b0b..13ad4e4df 100644 --- a/pkg/ring0/entry_amd64.go +++ b/pkg/ring0/entry_amd64.go @@ -39,11 +39,6 @@ func sysenter() // assembly to get the ABI0 (i.e., primary) address. func addrOfSysenter() uintptr -// swapgs swaps the current GS value. -// -// This must be called prior to sysret/iret. -func swapgs() - // jumpToKernel jumps to the kernel version of the current RIP. func jumpToKernel() -- cgit v1.2.3