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/lib_amd64.go | 42 ++---------------------------------------- 1 file changed, 2 insertions(+), 40 deletions(-) (limited to 'pkg/ring0/lib_amd64.go') diff --git a/pkg/ring0/lib_amd64.go b/pkg/ring0/lib_amd64.go index 05c394ff5..c42a5b205 100644 --- a/pkg/ring0/lib_amd64.go +++ b/pkg/ring0/lib_amd64.go @@ -21,29 +21,6 @@ import ( "gvisor.dev/gvisor/pkg/cpuid" ) -// LoadFloatingPoint loads floating point state by the most efficient mechanism -// available (set by Init). -var LoadFloatingPoint func(*byte) - -// SaveFloatingPoint saves floating point state by the most efficient mechanism -// available (set by Init). -var SaveFloatingPoint func(*byte) - -// fxrstor uses fxrstor64 to load floating point state. -func fxrstor(*byte) - -// xrstor uses xrstor to load floating point state. -func xrstor(*byte) - -// fxsave uses fxsave64 to save floating point state. -func fxsave(*byte) - -// xsave uses xsave to save floating point state. -func xsave(*byte) - -// xsaveopt uses xsaveopt to save floating point state. -func xsaveopt(*byte) - // writeFS sets the FS base address (selects one of wrfsbase or wrfsmsr). func writeFS(addr uintptr) @@ -53,8 +30,8 @@ func wrfsbase(addr uintptr) // wrfsmsr writes to the GS_BASE MSR. func wrfsmsr(addr uintptr) -// WriteGS sets the GS address (set by init). -var WriteGS func(addr uintptr) +// writeGS sets the GS address (selects one of wrgsbase or wrgsmsr). +func writeGS(addr uintptr) // wrgsbase writes to the GS base address. func wrgsbase(addr uintptr) @@ -106,19 +83,4 @@ func Init(featureSet *cpuid.FeatureSet) { hasXSAVE = featureSet.UseXsave() hasFSGSBASE = featureSet.HasFeature(cpuid.X86FeatureFSGSBase) validXCR0Mask = uintptr(featureSet.ValidXCR0Mask()) - if hasXSAVEOPT { - SaveFloatingPoint = xsaveopt - LoadFloatingPoint = xrstor - } else if hasXSAVE { - SaveFloatingPoint = xsave - LoadFloatingPoint = xrstor - } else { - SaveFloatingPoint = fxsave - LoadFloatingPoint = fxrstor - } - if hasFSGSBASE { - WriteGS = wrgsbase - } else { - WriteGS = wrgsmsr - } } -- cgit v1.2.3