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Import null pointer information from PDG into static analysis #1086

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Import null pointer information from PDG into static analysis #1086

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Commits on Jun 15, 2024

  1. Handle nested fields and other projections 

    Record field and index projections for pointers
by recording a Project event with a base and target
pointer pair.
    @ahomescu
    ahomescu committed Jun 15, 2024
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  2. Build PDG exclusively on provenance 

    The event source- and assignment-based PDG
construction steps were giving incorrect results
for indirect accesses, so remove them completely.
    @ahomescu
    ahomescu committed Jun 15, 2024
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  3. Pointer provenance improvements 

    Track the provenance of pointers with finer granularity
by storing the size of every allocation, local, and constant
inside the corresponding events. With this information, we can
keep track of the boundaries of every object and track whether
a projected pointer falls inside the original allocation.
    @ahomescu
    ahomescu committed Jun 15, 2024
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  4. Add size of locals to AddrOfLocal events 

    Keep track of the size of every local for the
new provenance algorithm.
    @ahomescu
    ahomescu committed Jun 15, 2024
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  5. Add constant size information to events 

    Add a new AddrOfConst event and use it to keep
track of the sizes of all global constants for
the new provenance algorithm.
    @ahomescu
    ahomescu committed Jun 15, 2024
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  6. Add corner case for Offset(0, _, _) nodes 

    Handle Offset nodes with a base pointer of 0
where the offset is non-zero, potentially resulting
in a brand new pointer.

One such case occurs in mod_cgi from lighttpd:
    const uintptr_t baseptr = (uintptr_t)env->b->ptr;
    for (i = 0; i < env->oused; ++i)
            envp[i] += baseptr;
    @ahomescu
    ahomescu committed Jun 15, 2024
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  7. Add is_null flag to PDG graphs 

    Mark each PDG graph with a boolean flag that
represents whether that graph corresponds to the
null pointer or not. The PDG construction algorithm
seems to build one unique graph for all null pointers
in the entire program.
    @ahomescu
    ahomescu committed Jun 15, 2024
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  8. Add an extra null pointer test to analysis example 

    Add one test where a function argument can be either
null or non-null in the recur() function of the
analysis/tests/misc example code.
    @ahomescu
    ahomescu committed Jun 15, 2024
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  9. Use PDG to remove NON_NULL from pointers in static analysis 

    Remove the NON_NULL permission from all nodes in
the null graph from the PDG.
    @ahomescu
    ahomescu committed Jun 15, 2024
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