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decompiler: Fix extreme value checks in Funcdata::replaceLessequal #8698

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decompiler: Fix extreme value checks in Funcdata::replaceLessequal #8698

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12 changes: 12 additions & 0 deletions Ghidra/Features/Decompiler/src/decompile/cpp/address.hh
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Original file line number Diff line number Diff line change
Expand Up @@ -498,6 +498,18 @@ inline bool Range::contains(const Address &addr) const {
/// \return a value appropriate for masking off the first \e size bytes
inline uintb calc_mask(int4 size) { return uintbmasks[((uint4)size) < 8 ? size : 8]; }

/// \param size of the integer in bytes
/// \return largest unsigned integer value for given size
inline uintb calc_uint_max(int4 size) { return calc_mask(size); }

/// \param size of the integer in bytes
/// \return largest signed integer value for given size
inline uintb calc_int_max(int4 size) { return calc_mask(size) >> 1; }

/// \param size of the integer in bytes
/// \return smallest signed integer value for given size
inline uintb calc_int_min(int4 size) { return (uintb)1 << (size * 8 - 1); }

/// Perform a CPUI_INT_RIGHT on the given val
/// \param val is the value to shift
/// \param sa is the number of bits to shift
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14 changes: 8 additions & 6 deletions Ghidra/Features/Decompiler/src/decompile/cpp/funcdata_op.cc
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Original file line number Diff line number Diff line change
Expand Up @@ -1031,7 +1031,8 @@ bool Funcdata::replaceLessequal(PcodeOp *op)
{
Varnode *vn;
int4 i;
intb val,diff;
uintb val;
intb diff;

if ((vn=op->getIn(0))->isConstant()) {
diff = -1;
Expand All @@ -1044,15 +1045,16 @@ bool Funcdata::replaceLessequal(PcodeOp *op)
else
return false;

val = sign_extend(vn->getOffset(),8*vn->getSize()-1);
val = vn->getOffset();
if (op->code() == CPUI_INT_SLESSEQUAL) {
if ((val<0)&&(val+diff>0)) return false; // Check for sign overflow
if ((val>0)&&(val+diff<0)) return false;
// Check for signed overflow
if ((diff == -1) && (val == calc_int_min(vn->getSize()))) return false;
if ((diff == 1) && (val == calc_int_max(vn->getSize()))) return false;
opSetOpcode(op,CPUI_INT_SLESS);
}
else { // Check for unsigned overflow
if ((diff==-1)&&(val==0)) return false;
if ((diff==1)&&(val==-1)) return false;
if ((diff == -1) && (val == 0)) return false;
if ((diff == 1) && (val == calc_uint_max(vn->getSize()))) return false;
opSetOpcode(op,CPUI_INT_LESS);
}
uintb res = (val+diff) & calc_mask(vn->getSize());
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