[PATCH v2 1/2] RISC-V: Fix buffer overflow on print_insn_riscv

[Tsukasa OI]

On 2022/10/04 18:58, Jan Beulich wrote:
> On 04.10.2022 11:45, Tsukasa OI wrote:
>> --- a/include/opcode/riscv.h
>> +++ b/include/opcode/riscv.h
>> @@ -55,6 +55,8 @@ static const char * const riscv_pred_succ[16] =
>>    "i", "iw", "ir", "irw", "io", "iow", "ior", "iorw"
>>  };
>>  
>> +#define RISCV_MAX_INSN_LEN 22  /* max 176-bit encoding.  */
> 
> To be honest this still doesn't look sufficient to me: There's still
> no connection between this constant and riscv_insn_length(). Yet both
> want changing at the same time when it comes to insn length aspects.
> As said in reply to v1 - comments may be one way of dealing with this.
> We don't have BUILD_BUG_ON() or alike (and even if we had it wouldn't
> be usable in a portable way), so an actual build time check might not
> be feasible. A runtime check also doesn't look realistic, as
> 
>     gas_assert (riscv_insn_length(~0) == RISCV_MAX_INSN_LEN);
> 
> wouldn't be correct, and I'm unconvinced of using other than the most
> simple ~0 as an argument here.
> 
> Jan
> 

I have to agree that the constant with no direct connection with
riscv_insn_length is not good but I don't come up with better solution
than this (with given constraints).
In any case, keeping this stack buffer overflow is definitely a bad idea
and we have to do something to deal with it in a days.

Tsukasa