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Diffstat (limited to 'pkg/sentry/arch/arch_amd64.s')
| -rw-r--r-- | pkg/sentry/arch/arch_amd64.s | 135 |
1 files changed, 135 insertions, 0 deletions
diff --git a/pkg/sentry/arch/arch_amd64.s b/pkg/sentry/arch/arch_amd64.s new file mode 100644 index 000000000..10d621b6d --- /dev/null +++ b/pkg/sentry/arch/arch_amd64.s @@ -0,0 +1,135 @@ +// Copyright 2018 Google Inc. +// +// 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. + +#include "textflag.h" + +// MXCSR_DEFAULT is the reset value of MXCSR (Intel SDM Vol. 2, Ch. 3.2 +// "LDMXCSR") +#define MXCSR_DEFAULT 0x1f80 + +// MXCSR_OFFSET is the offset in bytes of the MXCSR field from the start of the +// FXSAVE/XSAVE area. (Intel SDM Vol. 1, Table 10-2 "Format of an FXSAVE Area") +#define MXCSR_OFFSET 24 + +// initX86FPState initializes floating point state. +// +// func initX86FPState(data *FloatingPointData, useXsave bool) +// +// We need to clear out and initialize an empty fp state area since the sentry +// may have left sensitive information in the floating point registers. +// +// Preconditions: data is zeroed +TEXT ·initX86FPState(SB), $24-16 + // Save MXCSR (callee-save) + STMXCSR mxcsr-8(SP) + + // Save x87 CW (callee-save) + FSTCW cw-16(SP) + + MOVQ fpState+0(FP), DI + + // Do we use xsave? + MOVBQZX useXsave+8(FP), AX + TESTQ AX, AX + JZ no_xsave + + // Use XRSTOR to clear all FP state to an initial state. + // + // The fpState XSAVE area is zeroed on function entry, meaning + // XSTATE_BV is zero. + // + // "If RFBM[i] = 1 and bit i is clear in the XSTATE_BV field in the + // XSAVE header, XRSTOR initializes state component i." + // + // Initialization is defined in SDM Vol 1, Chapter 13.3. It puts all + // the registers in a reasonable initial state, except MXCSR: + // + // "The MXCSR register is part of state component 1, SSE state (see + // Section 13.5.2). However, the standard form of XRSTOR loads the + // MXCSR register from memory whenever the RFBM[1] (SSE) or RFBM[2] + // (AVX) is set, regardless of the values of XSTATE_BV[1] and + // XSTATE_BV[2]." + + // Set MXCSR to the default value. + MOVL $MXCSR_DEFAULT, MXCSR_OFFSET(DI) + + // Initialize registers with XRSTOR. + MOVL $0xffffffff, AX + MOVL $0xffffffff, DX + BYTE $0x48; BYTE $0x0f; BYTE $0xae; BYTE $0x2f // XRSTOR64 0(DI) + + // Now that all the state has been reset, write it back out to the + // XSAVE area. + BYTE $0x48; BYTE $0x0f; BYTE $0xae; BYTE $0x27 // XSAVE64 0(DI) + + JMP out + +no_xsave: + // Clear out existing X values. + PXOR X0, X0 + MOVO X0, X1 + MOVO X0, X2 + MOVO X0, X3 + MOVO X0, X4 + MOVO X0, X5 + MOVO X0, X6 + MOVO X0, X7 + MOVO X0, X8 + MOVO X0, X9 + MOVO X0, X10 + MOVO X0, X11 + MOVO X0, X12 + MOVO X0, X13 + MOVO X0, X14 + MOVO X0, X15 + + // Zero out %rax and store into MMX registers. MMX registers are + // an alias of 8x64 bits of the 8x80 bits used for the original + // x87 registers. Storing zero into them will reset the FPU registers + // to bits [63:0] = 0, [79:64] = 1. But the contents aren't too + // important, just the fact that we have reset them to a known value. + XORQ AX, AX + MOVQ AX, M0 + MOVQ AX, M1 + MOVQ AX, M2 + MOVQ AX, M3 + MOVQ AX, M4 + MOVQ AX, M5 + MOVQ AX, M6 + MOVQ AX, M7 + + // The Go assembler doesn't support FNINIT, so we use BYTE. + // This will: + // - Reset FPU control word to 0x037f + // - Clear FPU status word + // - Reset FPU tag word to 0xffff + // - Clear FPU data pointer + // - Clear FPU instruction pointer + BYTE $0xDB; BYTE $0xE3; // FNINIT + + // Reset MXCSR. + MOVL $MXCSR_DEFAULT, tmpmxcsr-24(SP) + LDMXCSR tmpmxcsr-24(SP) + + // Save the floating point state with fxsave. + FXSAVE64 0(DI) + +out: + // Restore MXCSR. + LDMXCSR mxcsr-8(SP) + + // Restore x87 CW. + FLDCW cw-16(SP) + + RET |