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try_access: use checked_add instead of overflowing_add #273

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try_access: use checked_add instead of overflowing_add #273

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Commits on Nov 28, 2023

  1. try_access: use checked_add instead of overflowing_add 

    We were allowing overflows if the overflow value would've been 0.
This can be problematic if there is a memory region that starts
at GuestAddress(0x0), but the access was not intended to spill
into that region. We don't consider memory to be a circular ring
buffer which would be the only situation in which we should allow
overflowing accesses.

While at it, also refactor the checked_add for the toal number of
bytes to use `ok_or` instead of a match pattern, as this is
easier to read.

Writing a regression test for the overflowing add is not possible
with the current infrastructure because GuestMemoryMmap does not
allow creating memory regions with an access that would overflow
(i.e. having a memory region starting at u64::MAX of size 1).
Also, we cannot call try_access with a size bigger than the
memory region size because we only allow accesses that fit in
the memory region.

Signed-off-by: Andreea Florescu <[email protected]>
    @andreeaflorescu
    andreeaflorescu committed Nov 28, 2023
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