Harden against invalid alignment

[SoniEx2]

Chasing https://crbug.com/oss-fuzz/51561

Let's see if this breaks anything...

The issue only triggers if both conditions are true:

• Multi-memory is enabled
• Alignment (masked) is between 32 and 63

[SoniEx2]

cc @keithw because oss-fuzz

[keithw]

Thank you for fixing this!

[SoniEx2]

ping @keithw @sbc100 (tests have also been upstreamed, tho wabt is currently a bit out of date on spec tests)

[keithw]

Thanks, and thanks for the ping. Do you think it would be better to consolidate the three ReadAlignment, TakeHasMemidx, and CheckAlignment functions into a single ReadAlignment(Address* align_log2, bool* has_memidx, const char* desc); that just does everything? That seems safer than requiring the caller to remember to call CheckAlignment each time (if ReadAlignment just always does it).

[keithw]

E.g. keithw/wabt@b09d4e0

[SoniEx2]

we figured having the check in the same function is what caused the issue in the first place. further, different contexts may give different meanings to the alignment flags, so we would be against calling it "has memidx" in that case.

would you have another way to enforce that CheckAlignment is called?

[SoniEx2]

how about this?

[keithw]

Let's just go back to the way you had it and call it done.

[SoniEx2]

oh ;-; okay