Re: [PATCH] Fix implicit signed to unsigned conversion in PVM_VAL_BOX

[Jose E. Marchesi]

Hi Tim.

    Found by libFuzzer:
    pvm-program.c:74:11: runtime error: implicit conversion from type 'int' of
    value -8 (32-bit, signed) to type 'unsigned long' changed the value to
    18446744073709551608 (64-bit, unsigned)
    
    2020-04-10  Tim Rühsen  <address@hidden>
    
           * lib/pvm.h (PVM_VAL_BOX): Fix implicit signed
           to unsigned conversion.
    ---
     ChangeLog | 5 +++++
     lib/pvm.h | 2 +-
     2 files changed, 6 insertions(+), 1 deletion(-)
    
    diff --git a/lib/pvm.h b/lib/pvm.h
    index 3fbb513b..e1a06d65 100644
    --- a/lib/pvm.h
    +++ b/lib/pvm.h
    @@ -143,7 +143,7 @@ pvm_val pvm_make_ulong (uint64_t value, int size);
        all pointers are aligned to 8 bytes.  The allocator for the boxed
        values makes sure this is always the case.  */
    
    -#define PVM_VAL_BOX(V) ((pvm_val_box) ((((uintptr_t) V) & ~0x7)))
    +#define PVM_VAL_BOX(V) ((pvm_val_box) ((((uintptr_t) V) & ~0x7U)))
    
     /* This constructor should be used in order to build boxes.  */
    
I just reverted this commit, as it broke master badly.

The operation above actually depends on ~0x7 to be sign-extended to
whatever size uintptr_t is.

Does this pacify your fuzzer?:

#define PVM_VAL_BOX(V) ((pvm_val_box) ((((uintptr_t) V)
                                         & ~((uintptr_t)0x7U))))