Messages in this thread | | | Date | Tue, 21 Dec 2021 09:56:17 +0000 | From | "Russell King (Oracle)" <> | Subject | Re: [PATCH] asm/sections: fix memory object end check |
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On Tue, Dec 21, 2021 at 08:06:24AM +0100, Alexander Gordeev wrote: > Function memory_contains() checks whether a memory object is > entirely contained within a memory region. The condition that > checks the upper bound of the object against the upper bound > of the region is inclusive. That does not correspond to the > similar checks in memory_intersects() friend function, nor > to the actual regions memory_contains() is called against. > > In particular, __init_end address assumed do not belong to > the init section itself. Similarly, on ARM __idmap_text_end > and __entry_text_end are affected.
__init_end is exclusive as are the other symbols you mention here. They point at the byte immediately following the area.
When testing an virt + size, the resulting address of "virt + size" is always exclusive - this also points at the byte immediately following the range of addresses. The preceeding byte is part of the object.
For example, if size is one, then we have a single byte, which is at address "virt". "virt + 1" is not part of the object. Therefore, if size is 1MiB, then "virt + 1048576" is similarly not part of the object.
Hence, we _do_ want to test address + size <= end.
This code appears to me to be correct, and this patch _introduces_ a bug.
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