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Make jemalloc bound returned pointers to their usable size #2147

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Make jemalloc bound returned pointers to their usable size #2147

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Commits on Jul 24, 2024

  1. mrs: Add a feature to make MRS apply bounds to returned pointers

    @markjdb
    markjdb committed Jul 24, 2024
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  2. jemalloc: Avoid adding bounds unnecessarily 

    The memory returned by je_allocm() and je_rallocm() is allocated using
je_mallocx() and je_(x|r)allocx(), respectively, and those functions apply
bounds to their return values by virtue of being implemented using
imalloc().

This makes it easier to make jemalloc bound pointers to the usable size
instead of the allocation size.
    @markjdb
    markjdb committed Jul 24, 2024
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  3. jemalloc: Clamp in malloc_usable_size() only if a tag is present 

    This behaviour should be safe and is useful for testing whether the bounds
applied by jemalloc match what malloc_usable_size() reports.  That is, one
can validate bounds with a check like,

    assert(cheri_getlen(p) == malloc_usable_size(cheri_cleartag(p)));

In particular, malloc_usable_size() will look up the usable size using
allocator metadata, so it's handy to be able to compare that size with the
capability bounds.
    @markjdb
    markjdb committed Jul 24, 2024
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  4. jemalloc: Bound pointers to the usable size 

    Previously jemalloc would return pointers bounded to the allocation size,
which is stricter but makes realloc() loops slow since they force MRS to
make a new allocation.  Instead, bound returned pointers to their usable
size; MRS can now optionally further tighten bounds if so desired.
    @markjdb
    markjdb committed Jul 24, 2024
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