decompiler: Fix extreme value checks in Funcdata::replaceLessequal #8698
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Fixes NationalSecurityAgency#8696 The checks for extreme values when transforming <= to < were incomplete and relied on undefined behavior, making compilers optimize them out. Specifically, for SLESS_EQUAL, the decompiler relied on integer overflows. For integers smaller than 8 bytes, no overflow will occur when adding 1, resulting in a missed case and, thus, x <= INT_MAX will become x < INT_MIN. For the signed case when subtracting one, the compiler removes the check due to undefined behavior, resulting in another missed case. To fix this, add helper functions for computing maximum and minimum values for signed and unsigned varnodes and directly check for them.
ryanmkurtz
added
Feature: Decompiler
Status: Triage
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Fixes #8696
The checks for extreme values when transforming <= to < were incomplete and relied on undefined behavior, making compilers optimize them out.
Specifically, for SLESS_EQUAL, the decompiler relied on integer overflows. For integers smaller than 8 bytes, no overflow will occur when adding 1, resulting in a missed case and, thus, x <= INT_MAX will become x < INT_MIN. For the signed case when subtracting one, the compiler removes the check due to undefined behavior, resulting in another missed case.
To fix this, add helper functions for computing maximum and minimum values for signed and unsigned varnodes and directly check for them.