HomePhabricator

[ubsan] Detect invalid unsigned pointer index expression (clang)

Description

[ubsan] Detect invalid unsigned pointer index expression (clang)

Adding an unsigned offset to a base pointer has undefined behavior if
the result of the expression would precede the base. An example from
@regehr:

int foo(char *p, unsigned offset) {
  return p + offset >= p; // This may be optimized to '1'.
}

foo(p, -1); // UB.

This patch extends the pointer overflow check in ubsan to detect invalid
unsigned pointer index expressions. It changes the instrumentation to
only permit non-negative offsets in pointer index expressions when all
of the GEP indices are unsigned.

Testing: check-llvm, check-clang run on a stage2, ubsan-instrumented
build.

Differential Revision: https://reviews.llvm.org/D33910

Details

Committed
vedantkJun 12 2017, 11:42 AM
Differential Revision
D33910: [ubsan] Detect invalid unsigned pointer index expression (clang)
Parents
rL305215: Address David Blaikie comment by replacing grep with FileCheck.
Branches
Unknown
Tags
Unknown