[BUG] cmse spec: cmse_check_address_range() example impl. doesn't check for size==0

[lersek]

Describe the bug

acle/cmse/cmse.md

Line 1592 in d294acf

char *pe = pb + s – 1;

If s is zero, then pe is set just below pb -- or in case pb is zero, we wrap around 0 downwards, to the maximum possible pointer value. In either of those cases, all the subsequent cmse_TT* invocations get bogus pe values.

Arguably, if the caller intends to access zero bytes, we should immediately fail, or immediately validate, the intent (I could see arguments for either outcome). What we should probably not do is call cmse_TT* at all.

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