54 lines
2.7 KiB
Plaintext
54 lines
2.7 KiB
Plaintext
$OpenBSD: patch-include_llvm_CodeGen_MachineFrameInfo_h,v 1.2 2018/08/21 06:56:09 ajacoutot Exp $
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- Add RETGUARD to clang for amd64. This security mechanism uses per-function
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random cookies to protect access to function return instructions, with the
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effect that the integrity of the return address is protected, and function
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return instructions are harder to use in ROP gadgets.
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On function entry the return address is combined with a per-function random
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cookie and stored in the stack frame. The integrity of this value is verified
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before function return, and if this check fails, the program aborts. In this way
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RETGUARD is an improved stack protector, since the cookies are per-function. The
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verification routine is constructed such that the binary space immediately
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before each ret instruction is padded with int03 instructions, which makes these
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return instructions difficult to use in ROP gadgets. In the kernel, this has the
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effect of removing approximately 50% of total ROP gadgets, and 15% of unique
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ROP gadgets compared to the 6.3 release kernel. Function epilogues are
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essentially gadget free, leaving only the polymorphic gadgets that result from
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jumping into the instruction stream partway through other instructions. Work to
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remove these gadgets will continue through other mechanisms.
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- Refactor retguard to make adding additional arches easier.
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Index: include/llvm/CodeGen/MachineFrameInfo.h
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--- include/llvm/CodeGen/MachineFrameInfo.h.orig
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+++ include/llvm/CodeGen/MachineFrameInfo.h
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@@ -237,6 +237,13 @@ class MachineFrameInfo {
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/// The frame index for the stack protector.
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int StackProtectorIdx = -1;
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+ struct ReturnProtector {
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+ /// The register to use for return protector calculations
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+ unsigned Register = 0;
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+ /// Set to true if this function needs return protectors
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+ bool Needed = false;
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+ } RPI;
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+
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/// The frame index for the function context. Used for SjLj exceptions.
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int FunctionContextIdx = -1;
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@@ -313,6 +320,14 @@ class MachineFrameInfo {
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int getStackProtectorIndex() const { return StackProtectorIdx; }
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void setStackProtectorIndex(int I) { StackProtectorIdx = I; }
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bool hasStackProtectorIndex() const { return StackProtectorIdx != -1; }
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+
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+ /// Get / Set return protector calculation register
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+ unsigned getReturnProtectorRegister() const { return RPI.Register; }
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+ void setReturnProtectorRegister(unsigned I) { RPI.Register = I; }
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+ bool hasReturnProtectorRegister() const { return RPI.Register != 0; }
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+ /// Get / Set if this frame needs a return protector
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+ void setReturnProtectorNeeded(bool I) { RPI.Needed = I; }
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+ bool getReturnProtectorNeeded() const { return RPI.Needed; }
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/// Return the index for the function context object.
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/// This object is used for SjLj exceptions.
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