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Deny dynamic JMP/JNE backwards jumps in predicates #359

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Jun 21, 2022
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Deny dynamic JMP/JNE backwards jumps in predicates #359

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2 changes: 1 addition & 1 deletion specs/vm/main.md
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Expand Up @@ -109,7 +109,7 @@ For each such input in the transaction, the VM is [initialized](#vm-initializati
During predicate mode, hitting any of the following instructions causes predicate verification to halt, returning Boolean `false`:

1. Any [contract instruction](./instruction_set.md#contract-instructions).
1. [JI](./instruction_set.md#ji-jump-immediate) or [JNEI](./instruction_set.md#jnei-jump-if-not-equal-immediate) with jump-to value less than or equal to `$pc` (these would allow loops). In other words, `$pc` must be strictly increasing.
1. [JI](./instruction_set.md#ji-jump-immediate), [JNEI](./instruction_set.md#jnei-jump-if-not-equal-immediate), [JMP](./instruction_set.md#jmp-jump) or [JNE](./instruction_set.md#jne-jump-if-not-equal) with jump-to value less than or equal to `$pc` (these would allow loops). In other words, `$pc` must be strictly increasing.

In addition, during predicate mode if `$pc` is set to a value greater than the end of predicate bytecode (this would allow bytecode outside the actual predicate), predicate verification halts returning Boolean `false`.

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