[PATCH] RISC-V: hwprobe: Check for the reserved flags

[Andrew Jones]

Hi Palmer,

On Wed, Jan 03, 2024 at 04:12:20AM -0800, Palmer Dabbelt wrote:
> This check got dropped when RISCV_HWPROBE_WHICH_CPUS was added, but
> we've still got a bunch of other reserved flags.  So check for them,
> just to make sure userspace doesn't get confused later.
> 
> Fixes: e178bf146e4b ("RISC-V: hwprobe: Introduce which-cpus flag")

I'm having trouble finding the tree/branch for this commit hash.

> Signed-off-by: Palmer Dabbelt <palmer at rivosinc.com>
> ---
>  arch/riscv/kernel/sys_hwprobe.c | 4 ++++
>  1 file changed, 4 insertions(+)
> 
> diff --git a/arch/riscv/kernel/sys_hwprobe.c b/arch/riscv/kernel/sys_hwprobe.c
> index ccf61b040536..10d72893b04f 100644
> --- a/arch/riscv/kernel/sys_hwprobe.c
> +++ b/arch/riscv/kernel/sys_hwprobe.c
> @@ -347,6 +347,10 @@ static int do_riscv_hwprobe(struct riscv_hwprobe __user *pairs,
>  			    unsigned long __user *cpus_user,
>  			    unsigned int flags)
>  {
> +	/* The rest of the flags are still reserved. */
> +	if (flags & ~RISCV_HWPROBE_WICHH_CPUS)
                                   ^ WHICH


We shouldn't need this check since the way v3 of the series has
do_riscv_hwprobe() is

 static int do_riscv_hwprobe(struct riscv_hwprobe __user *pairs,
                           size_t pair_count, size_t cpusetsize,
                           unsigned long __user *cpus_user,
                           unsigned int flags)
 {
       if (flags & RISCV_HWPROBE_WHICH_CPUS)
               return hwprobe_get_cpus(pairs, pair_count, cpusetsize,
                                       cpus_user, flags);

       return hwprobe_get_values(pairs, pair_count, cpusetsize,
                                 cpus_user, flags);
 }

And hwprobe_get_cpus() starts with this check

      if (flags != RISCV_HWPROBE_WHICH_CPUS)
               return -EINVAL;

And hwprobe_get_values() starts with the original check

      /* Check the reserved flags. */
      if (flags != 0)
              return -EINVAL;


IOW, we don't check flags at the top level, but each branch checks for its
flags and hwprobe_get_values() doesn't have any.

Thanks,
drew

> +		return -EINVAL;
> +
>  	if (flags & RISCV_HWPROBE_WHICH_CPUS)
>  		return hwprobe_get_cpus(pairs, pair_count, cpusetsize,
>  					cpus_user, flags);
> -- 
> 2.43.0
>