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Merge pull request google#2321 from lubinszARM:pr_nogo
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// 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. | ||
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// +build arm64 | ||
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package ring0 | ||
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import ( | ||
"reflect" | ||
"syscall" | ||
"unsafe" | ||
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"gvisor.dev/gvisor/pkg/safecopy" | ||
"gvisor.dev/gvisor/pkg/usermem" | ||
) | ||
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const ( | ||
nopInstruction = 0xd503201f | ||
instSize = unsafe.Sizeof(uint32(0)) | ||
vectorsRawLen = 0x800 | ||
) | ||
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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 | ||
} | ||
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// 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() | ||
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// 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") | ||
} | ||
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vectorsSafeTable := unsafeSlice(vectorsBegin, vectorsSafeLen) // Now a []uint32 | ||
vectorsRawLen32 := vectorsRawLen / int(instSize) | ||
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offset := vectorsBegin & (1<<11 - 1) | ||
if offset != 0 { | ||
offset = 1<<11 - offset | ||
} | ||
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pageBegin := (vectorsBegin + offset) & ^uintptr(usermem.PageSize-1) | ||
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_, _, 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()) | ||
} | ||
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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] | ||
} | ||
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// 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) | ||
} | ||
} | ||
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_, _, errno = syscall.Syscall(syscall.SYS_MPROTECT, uintptr(pageBegin), uintptr(usermem.PageSize), uintptr(syscall.PROT_READ|syscall.PROT_EXEC)) | ||
if errno != 0 { | ||
panic(errno.Error()) | ||
} | ||
} |
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