Go 1.17 support for the KVM platform

Go 1.17 adds a new register-based calling convention. While transparent for
most applications, the KVM platform needs special work in a few cases.

First of all, we need the actual address of some assembly functions, rather
than the address of a wrapper. See http://gvisor.dev/pr/5832 for complete
discussion of this.

More relevant to this CL is that ABI0-to-ABIInternal wrappers (i.e., calls from
assembly to Go) access the G via FS_BASE. The KVM quite fast-and-loose about
the Go environment, often calling into (nosplit) Go functions with
uninitialized FS_BASE.

That will no longer work in Go 1.17, so this CL changes the platform to
consistently restore FS_BASE before calling into Go code.

This CL does not affect arm64 code. Go 1.17 does not support the register-based
calling convention for arm64 (it will come in 1.18), but arm64 also does not
use a non-standard register like FS_BASE for TLS, so it may not require any
changes.

PiperOrigin-RevId: 384234305

3 files changed, 83 insertions, 26 deletions

diff --git a/pkg/sentry/platform/kvm/testutil/testutil.go b/pkg/sentry/platform/kvm/testutil/testutil.go
index 5c1efa0fd..d8c273796 100644
--- a/pkg/sentry/platform/kvm/testutil/testutil.go
+++ b/pkg/sentry/platform/kvm/testutil/testutil.go
@@ -23,23 +23,41 @@ import (
 // Getpid executes a trivial system call.
 func Getpid()
 
-// Touch touches the value in the first register.
-func Touch()
+// AddrOfGetpid returns the address of Getpid.
+//
+// In Go 1.17+, Go references to assembly functions resolve to an ABIInternal
+// wrapper function rather than the function itself. We must reference from
+// assembly to get the ABI0 (i.e., primary) address.
+func AddrOfGetpid() uintptr
+
+// AddrOfTouch returns the address of a function that touches the value in the
+// first register.
+func AddrOfTouch() uintptr
+func touch()
 
-// SyscallLoop executes a syscall and loops.
-func SyscallLoop()
+// AddrOfSyscallLoop returns the address of a function that executes a syscall
+// and loops.
+func AddrOfSyscallLoop() uintptr
+func syscallLoop()
 
-// SpinLoop spins on the CPU.
-func SpinLoop()
+// AddrOfSpinLoop returns the address of a function that spins on the CPU.
+func AddrOfSpinLoop() uintptr
+func spinLoop()
 
-// HaltLoop immediately halts and loops.
-func HaltLoop()
+// AddrOfHaltLoop returns the address of a function that immediately halts and
+// loops.
+func AddrOfHaltLoop() uintptr
+func haltLoop()
 
-// TwiddleRegsFault twiddles registers then faults.
-func TwiddleRegsFault()
+// AddrOfTwiddleRegsFault returns the address of a function that twiddles
+// registers then faults.
+func AddrOfTwiddleRegsFault() uintptr
+func twiddleRegsFault()
 
-// TwiddleRegsSyscall twiddles registers then executes a syscall.
-func TwiddleRegsSyscall()
+// AddrOfTwiddleRegsSyscall returns the address of a function that twiddles
+// registers then executes a syscall.
+func AddrOfTwiddleRegsSyscall() uintptr
+func twiddleRegsSyscall()
 
 // FloatingPointWorks is a floating point test.
 //
diff --git a/pkg/sentry/platform/kvm/testutil/testutil_amd64.go b/pkg/sentry/platform/kvm/testutil/testutil_amd64.go
index 8048eedec..7c19b6a8f 100644
--- a/pkg/sentry/platform/kvm/testutil/testutil_amd64.go
+++ b/pkg/sentry/platform/kvm/testutil/testutil_amd64.go
@@ -22,12 +22,14 @@ import (
 	"gvisor.dev/gvisor/pkg/sentry/arch"
 )
 
-// TwiddleSegments reads segments into known registers.
-func TwiddleSegments()
+// AddrOfTwiddleSegments return the address of a function that reads segments
+// into known registers.
+func AddrOfTwiddleSegments() uintptr
+func twiddleSegments()
 
 // SetTestTarget sets the rip appropriately.
-func SetTestTarget(regs *arch.Registers, fn func()) {
-	regs.Rip = uint64(reflect.ValueOf(fn).Pointer())
+func SetTestTarget(regs *arch.Registers, fn uintptr) {
+	regs.Rip = uint64(fn)
 }
 
 // SetTouchTarget sets rax appropriately.
diff --git a/pkg/sentry/platform/kvm/testutil/testutil_amd64.s b/pkg/sentry/platform/kvm/testutil/testutil_amd64.s
index 491ec0c2a..65e7c05ea 100644
--- a/pkg/sentry/platform/kvm/testutil/testutil_amd64.s
+++ b/pkg/sentry/platform/kvm/testutil/testutil_amd64.s
@@ -25,27 +25,46 @@ TEXT ·Getpid(SB),NOSPLIT,$0
 	SYSCALL
 	RET
 
-TEXT ·Touch(SB),NOSPLIT,$0
+// func AddrOfGetpid() uintptr
+TEXT ·AddrOfGetpid(SB), $0-8
+	MOVQ $·Getpid(SB), AX
+	MOVQ AX, ret+0(FP)
+	RET
+
+TEXT ·touch(SB),NOSPLIT,$0
 start:
 	MOVQ 0(AX), BX // deref AX
 	MOVQ $39, AX   // getpid
 	SYSCALL
 	JMP start
 
-TEXT ·HaltLoop(SB),NOSPLIT,$0
-start:
-	HLT
-	JMP start
+// func AddrOfTouch() uintptr
+TEXT ·AddrOfTouch(SB), $0-8
+	MOVQ $·touch(SB), AX
+	MOVQ AX, ret+0(FP)
+	RET
 
-TEXT ·SyscallLoop(SB),NOSPLIT,$0
+TEXT ·syscallLoop(SB),NOSPLIT,$0
 start:
 	SYSCALL
 	JMP start
 
-TEXT ·SpinLoop(SB),NOSPLIT,$0
+// func AddrOfSyscallLoop() uintptr
+TEXT ·AddrOfSyscallLoop(SB), $0-8
+	MOVQ $·syscallLoop(SB), AX
+	MOVQ AX, ret+0(FP)
+	RET
+
+TEXT ·spinLoop(SB),NOSPLIT,$0
 start:
 	JMP start
 
+// func AddrOfSpinLoop() uintptr
+TEXT ·AddrOfSpinLoop(SB), $0-8
+	MOVQ $·spinLoop(SB), AX
+	MOVQ AX, ret+0(FP)
+	RET
+
 TEXT ·FloatingPointWorks(SB),NOSPLIT,$0-8
 	NO_LOCAL_POINTERS
 	MOVQ $1, AX
@@ -75,20 +94,32 @@ TEXT ·FloatingPointWorks(SB),NOSPLIT,$0-8
 	NOTQ DI; \
 	NOTQ SP;
 
-TEXT ·TwiddleRegsSyscall(SB),NOSPLIT,$0
+TEXT ·twiddleRegsSyscall(SB),NOSPLIT,$0
 	TWIDDLE_REGS()
 	SYSCALL
 	RET // never reached
 
-TEXT ·TwiddleRegsFault(SB),NOSPLIT,$0
+// func AddrOfTwiddleRegsSyscall() uintptr
+TEXT ·AddrOfTwiddleRegsSyscall(SB), $0-8
+	MOVQ $·twiddleRegsSyscall(SB), AX
+	MOVQ AX, ret+0(FP)
+	RET
+
+TEXT ·twiddleRegsFault(SB),NOSPLIT,$0
 	TWIDDLE_REGS()
 	JMP AX // must fault
 	RET // never reached
 
+// func AddrOfTwiddleRegsFault() uintptr
+TEXT ·AddrOfTwiddleRegsFault(SB), $0-8
+	MOVQ $·twiddleRegsFault(SB), AX
+	MOVQ AX, ret+0(FP)
+	RET
+
 #define READ_FS() BYTE $0x64; BYTE $0x48; BYTE $0x8b; BYTE $0x00;
 #define READ_GS() BYTE $0x65; BYTE $0x48; BYTE $0x8b; BYTE $0x00;
 
-TEXT ·TwiddleSegments(SB),NOSPLIT,$0
+TEXT ·twiddleSegments(SB),NOSPLIT,$0
 	MOVQ $0x0, AX
 	READ_GS()
 	MOVQ AX, BX
@@ -96,3 +127,9 @@ TEXT ·TwiddleSegments(SB),NOSPLIT,$0
 	READ_FS()
 	SYSCALL
 	RET // never reached
+
+// func AddrOfTwiddleSegments() uintptr
+TEXT ·AddrOfTwiddleSegments(SB), $0-8
+	MOVQ $·twiddleSegments(SB), AX
+	MOVQ AX, ret+0(FP)
+	RET