src/interpreter.rs: Fix left/right shifts implementation (mask offset) #100
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The current version of the BPF Instruction Set Specification specifies that "Shift operations use a mask of 0x3F (63) for 64-bit operations and 0x1F (31) for 32-bit operations" [0]. The current implementation is not compliant, and Rust complains if we overflow the number of bits we have when trying to shift. Let's fix it, and let's complete the test suite regarding left and right shift operations. Note: The JITs are not updated at this stage. The standard does not mention any difference between JIT and interpreter, but the kernel clearly considers the masking for the interpreter only. JIT-compilers are supposed to handle the overflow case in an implementation-defined (architecture-dependant) fashion. Kernel also use masking for shifts with registers only (not immediates) and handles overflows with immediates in the verifier by rejecting the programs. [0]: https://www.ietf.org/archive/id/draft-thaler-bpf-isa-02.html#section-3.1-18 Reported-by: HAPPY <pcy190@126.com> Signed-off-by: Quentin Monnet <quentin@isovalent.com>
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The current version of the BPF Instruction Set Specification specifies that "Shift operations use a mask of 0x3F (63) for 64-bit operations and 0x1F (31) for 32-bit operations".
The current implementation is not compliant, and Rust complains if we overflow the number of bits we have when trying to shift. Let's fix it, and let's complete the test suite regarding left and right shift operations.
Note: The JITs are not updated at this stage. The standard does no. mention any difference between JIT and interpreter, but the kernel clearly considers the masking for the interpreter only. JIT-compilers are supposed to handle the overflow case in an implementation-defined (architecture-dependant) fashion. Kernel also use masking for shifts with registers only (not immediates) and handles overflows with immediates in the verifier by rejecting the programs.
Fixes: #99