Re: [PATCH -next V8 06/14] riscv: convert to generic entry

[Guo Ren]

On Mon, Nov 28, 2022 at 12:26 AM Ben Hutchings <ben@xxxxxxxxxxxxxxx> wrote:
>
> On Thu, 2022-11-03 at 03:50 -0400, guoren@xxxxxxxxxx wrote:
> [...]
> > --- a/arch/riscv/kernel/sys_riscv.c
> > +++ b/arch/riscv/kernel/sys_riscv.c
> [...]
> > +asmlinkage void do_sys_ecall_u(struct pt_regs *regs)
> > +{
> > +     syscall_t syscall;
> > +     ulong nr = regs->a7;
> > +
> > +     regs->epc += 4;
> > +     regs->orig_a0 = regs->a0;
> > +     regs->a0 = -ENOSYS;
> > +
> > +     nr = syscall_enter_from_user_mode(regs, nr);
> > +#ifdef CONFIG_COMPAT
> > +     if ((regs->status & SR_UXL) == SR_UXL_32)
> > +             syscall = compat_sys_call_table[nr];
> > +     else
> > +#endif
> > +             syscall = sys_call_table[nr];
> > +
> > +     if (nr < NR_syscalls)
>
> This bounds check needs to be done before indexing the system call
> table, not after.
Yes, you are right. That would cause a wrong pointer bug. Here is the
new version:

asmlinkage void do_sys_ecall_u(struct pt_regs *regs)
{
        syscall_t syscall;
        ulong nr = regs->a7;

        regs->epc += 4;
        regs->orig_a0 = regs->a0;
        regs->a0 = -ENOSYS;

        nr = syscall_enter_from_user_mode(regs, nr);

        if (nr < NR_syscalls) {
#ifdef CONFIG_COMPAT
                if ((regs->status & SR_UXL) == SR_UXL_32)
                        syscall = compat_sys_call_table[nr];
                else
#endif
                        syscall = sys_call_table[nr];

                regs->a0 = syscall(regs->orig_a0, regs->a1, regs->a2,
                                   regs->a3, regs->a4, regs->a5, regs->a6);
        }
        syscall_exit_to_user_mode(regs);
}

>
> Ben.
>
> > +             regs->a0 = syscall(regs->orig_a0, regs->a1, regs->a2,
> > +                                regs->a3, regs->a4, regs->a5, regs->a6);
> > +     syscall_exit_to_user_mode(regs);
> > +}
> [...]
>
> --
> Ben Hutchings
> This sentence contradicts itself - no actually it doesn't.



-- 
Best Regards
 Guo Ren