ARM64 kvm: apply PCALIGN for exception vector alignment

As PCALIGN is available on golang asm for arm64.
https://golang.org/pkg/cmd/internal/obj/arm64/

No need to use rewriteVectors() to ensure
alignment of exception vector.

Signed-off-by: Howard Zhang <howard.zhang@arm.com>

4 files changed, 21 insertions, 202 deletions

diff --git a/pkg/sentry/platform/ring0/BUILD b/pkg/sentry/platform/ring0/BUILD
index 679b287c3..5d01d21dd 100644
--- a/pkg/sentry/platform/ring0/BUILD
+++ b/pkg/sentry/platform/ring0/BUILD
@@ -72,7 +72,6 @@ go_library(
         "lib_amd64.s",
         "lib_arm64.go",
         "lib_arm64.s",
-        "lib_arm64_unsafe.go",
         "ring0.go",
     ],
     visibility = ["//pkg/sentry:internal"],
diff --git a/pkg/sentry/platform/ring0/entry_arm64.s b/pkg/sentry/platform/ring0/entry_arm64.s
index f489ad352..266817d82 100644
--- a/pkg/sentry/platform/ring0/entry_arm64.s
+++ b/pkg/sentry/platform/ring0/entry_arm64.s
@@ -132,40 +132,6 @@
   MOVD offset+PTRACE_R29(reg), R29; \
   MOVD offset+PTRACE_R30(reg), R30;
 
-// NOP-s
-#define nop31Instructions() \
-        WORD $0xd503201f; \
-        WORD $0xd503201f; \
-        WORD $0xd503201f; \
-        WORD $0xd503201f; \
-        WORD $0xd503201f; \
-        WORD $0xd503201f; \
-        WORD $0xd503201f; \
-        WORD $0xd503201f; \
-        WORD $0xd503201f; \
-        WORD $0xd503201f; \
-        WORD $0xd503201f; \
-        WORD $0xd503201f; \
-        WORD $0xd503201f; \
-        WORD $0xd503201f; \
-        WORD $0xd503201f; \
-        WORD $0xd503201f; \
-        WORD $0xd503201f; \
-        WORD $0xd503201f; \
-        WORD $0xd503201f; \
-        WORD $0xd503201f; \
-        WORD $0xd503201f; \
-        WORD $0xd503201f; \
-        WORD $0xd503201f; \
-        WORD $0xd503201f; \
-        WORD $0xd503201f; \
-        WORD $0xd503201f; \
-        WORD $0xd503201f; \
-        WORD $0xd503201f; \
-        WORD $0xd503201f; \
-        WORD $0xd503201f; \
-        WORD $0xd503201f;
-
 #define ESR_ELx_EC_UNKNOWN	(0x00)
 #define ESR_ELx_EC_WFx		(0x01)
 /* Unallocated EC: 0x02 */
@@ -760,79 +726,43 @@ TEXT ·El0_error_invalid(SB),NOSPLIT,$0
 	B ·Shutdown(SB)
 
 // Vectors implements exception vector table.
+// The start address of exception vector table should be 11-bits aligned.
+// For detail, please refer to arm developer document:
+// https://developer.arm.com/documentation/100933/0100/AArch64-exception-vector-table
+// Also can refer to the code in linux kernel: arch/arm64/kernel/entry.S
 TEXT ·Vectors(SB),NOSPLIT,$0
+	PCALIGN $2048
 	B ·El1_sync_invalid(SB)
-	nop31Instructions()
+	PCALIGN $128
 	B ·El1_irq_invalid(SB)
-	nop31Instructions()
+	PCALIGN $128
 	B ·El1_fiq_invalid(SB)
-	nop31Instructions()
+	PCALIGN $128
 	B ·El1_error_invalid(SB)
-	nop31Instructions()
 
+	PCALIGN $128
 	B ·El1_sync(SB)
-	nop31Instructions()
+	PCALIGN $128
 	B ·El1_irq(SB)
-	nop31Instructions()
+	PCALIGN $128
 	B ·El1_fiq(SB)
-	nop31Instructions()
+	PCALIGN $128
 	B ·El1_error(SB)
-	nop31Instructions()
 
+	PCALIGN $128
 	B ·El0_sync(SB)
-	nop31Instructions()
+	PCALIGN $128
 	B ·El0_irq(SB)
-	nop31Instructions()
+	PCALIGN $128
 	B ·El0_fiq(SB)
-	nop31Instructions()
+	PCALIGN $128
 	B ·El0_error(SB)
-	nop31Instructions()
 
+	PCALIGN $128
 	B ·El0_sync_invalid(SB)
-	nop31Instructions()
+	PCALIGN $128
 	B ·El0_irq_invalid(SB)
-	nop31Instructions()
+	PCALIGN $128
 	B ·El0_fiq_invalid(SB)
-	nop31Instructions()
+	PCALIGN $128
 	B ·El0_error_invalid(SB)
-	nop31Instructions()
-
-	// The exception-vector-table is required to be 11-bits aligned.
-	// Please see Linux source code as reference: arch/arm64/kernel/entry.s.
-	// For gvisor, I defined it as 4K in length, filled the 2nd 2K part with NOPs.
-	// So that, I can safely move the 1st 2K part into the address with 11-bits alignment.
-	WORD $0xd503201f	//nop
-	nop31Instructions()
-	WORD $0xd503201f
-	nop31Instructions()
-	WORD $0xd503201f
-	nop31Instructions()
-	WORD $0xd503201f
-	nop31Instructions()
-
-	WORD $0xd503201f
-	nop31Instructions()
-	WORD $0xd503201f
-	nop31Instructions()
-	WORD $0xd503201f
-	nop31Instructions()
-	WORD $0xd503201f
-	nop31Instructions()
-
-	WORD $0xd503201f
-	nop31Instructions()
-	WORD $0xd503201f
-	nop31Instructions()
-	WORD $0xd503201f
-	nop31Instructions()
-	WORD $0xd503201f
-	nop31Instructions()
-
-	WORD $0xd503201f
-	nop31Instructions()
-	WORD $0xd503201f
-	nop31Instructions()
-	WORD $0xd503201f
-	nop31Instructions()
-	WORD $0xd503201f
-	nop31Instructions()
diff --git a/pkg/sentry/platform/ring0/lib_arm64.go b/pkg/sentry/platform/ring0/lib_arm64.go
index d91a09de1..842aa7e30 100644
--- a/pkg/sentry/platform/ring0/lib_arm64.go
+++ b/pkg/sentry/platform/ring0/lib_arm64.go
@@ -56,6 +56,4 @@ func SaveFloatingPoint(*byte)
 // Init sets function pointers based on architectural features.
 //
 // This must be called prior to using ring0.
-func Init() {
-	rewriteVectors()
-}
+func Init() {}
diff --git a/pkg/sentry/platform/ring0/lib_arm64_unsafe.go b/pkg/sentry/platform/ring0/lib_arm64_unsafe.go
deleted file mode 100644
index c05166fea..000000000
--- a/pkg/sentry/platform/ring0/lib_arm64_unsafe.go
+++ /dev/null
@@ -1,108 +0,0 @@
-// Copyright 2019 The gVisor Authors.
-//
-// Licensed under the Apache License, Version 2.0 (the "License");
-// you may not use this file except in compliance with the License.
-// You may obtain a copy of the License at
-//
-//     http://www.apache.org/licenses/LICENSE-2.0
-//
-// Unless required by applicable law or agreed to in writing, software
-// distributed under the License is distributed on an "AS IS" BASIS,
-// WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
-// See the License for the specific language governing permissions and
-// limitations under the License.
-
-// +build arm64
-
-package ring0
-
-import (
-	"reflect"
-	"syscall"
-	"unsafe"
-
-	"gvisor.dev/gvisor/pkg/safecopy"
-	"gvisor.dev/gvisor/pkg/usermem"
-)
-
-const (
-	nopInstruction = 0xd503201f
-	instSize       = unsafe.Sizeof(uint32(0))
-	vectorsRawLen  = 0x800
-)
-
-func unsafeSlice(addr uintptr, length int) (slice []uint32) {
-	hdr := (*reflect.SliceHeader)(unsafe.Pointer(&slice))
-	hdr.Data = addr
-	hdr.Len = length / int(instSize)
-	hdr.Cap = length / int(instSize)
-	return slice
-}
-
-// Work around: move ring0.Vectors() into a specific address with 11-bits alignment.
-//
-// According to the design documentation of Arm64,
-// the start address of exception vector table should be 11-bits aligned.
-// Please see the code in linux kernel as reference: arch/arm64/kernel/entry.S
-// But, we can't align a function's start address to a specific address by using golang.
-// We have raised this question in golang community:
-// https://groups.google.com/forum/m/#!topic/golang-dev/RPj90l5x86I
-// This function will be removed when golang supports this feature.
-//
-// There are 2 jobs were implemented in this function:
-// 1, move the start address of exception vector table into the specific address.
-// 2, modify the offset of each instruction.
-func rewriteVectors() {
-	vectorsBegin := reflect.ValueOf(Vectors).Pointer()
-
-	// The exception-vector-table is required to be 11-bits aligned.
-	// And the size is 0x800.
-	// Please see the documentation as reference:
-	// https://developer.arm.com/docs/100933/0100/aarch64-exception-vector-table
-	//
-	// But, golang does not allow to set a function's address to a specific value.
-	// So, for gvisor, I defined the size of exception-vector-table as 4K,
-	// filled the 2nd 2K part with NOP-s.
-	// So that, I can safely move the 1st 2K part into the address with 11-bits alignment.
-	//
-	// So, the prerequisite for this function to work correctly is:
-	// vectorsSafeLen >= 0x1000
-	// vectorsRawLen  = 0x800
-	vectorsSafeLen := int(safecopy.FindEndAddress(vectorsBegin) - vectorsBegin)
-	if vectorsSafeLen < 2*vectorsRawLen {
-		panic("Can't update vectors")
-	}
-
-	vectorsSafeTable := unsafeSlice(vectorsBegin, vectorsSafeLen) // Now a []uint32
-	vectorsRawLen32 := vectorsRawLen / int(instSize)
-
-	offset := vectorsBegin & (1<<11 - 1)
-	if offset != 0 {
-		offset = 1<<11 - offset
-	}
-
-	pageBegin := (vectorsBegin + offset) & ^uintptr(usermem.PageSize-1)
-
-	_, _, errno := syscall.Syscall(syscall.SYS_MPROTECT, uintptr(pageBegin), uintptr(usermem.PageSize), uintptr(syscall.PROT_READ|syscall.PROT_WRITE|syscall.PROT_EXEC))
-	if errno != 0 {
-		panic(errno.Error())
-	}
-
-	offset = offset / instSize // By index, not bytes.
-	// Move exception-vector-table into the specific address, should uses memmove here.
-	for i := 1; i <= vectorsRawLen32; i++ {
-		vectorsSafeTable[int(offset)+vectorsRawLen32-i] = vectorsSafeTable[vectorsRawLen32-i]
-	}
-
-	// Adjust branch since instruction was moved forward.
-	for i := 0; i < vectorsRawLen32; i++ {
-		if vectorsSafeTable[int(offset)+i] != nopInstruction {
-			vectorsSafeTable[int(offset)+i] -= uint32(offset)
-		}
-	}
-
-	_, _, errno = syscall.Syscall(syscall.SYS_MPROTECT, uintptr(pageBegin), uintptr(usermem.PageSize), uintptr(syscall.PROT_READ|syscall.PROT_EXEC))
-	if errno != 0 {
-		panic(errno.Error())
-	}
-}