Re: [PATCH] riscv: reject invalid syscalls below -1

[David Abdurachmanov]

On Wed, Dec 18, 2019 at 11:46 AM Andreas Schwab <schwab@xxxxxxx> wrote:
>
> On Dez 18 2019, David Abdurachmanov wrote:
>
> > diff --git a/arch/riscv/kernel/entry.S b/arch/riscv/kernel/entry.S
> > index a1349ca64669..e163b7b64c86 100644
> > --- a/arch/riscv/kernel/entry.S
> > +++ b/arch/riscv/kernel/entry.S
> > @@ -246,6 +246,7 @@ check_syscall_nr:
> >        */
> >       li t1, -1
> >       beq a7, t1, ret_from_syscall_rejected
> > +     blt a7, t1, 1f
>
> How about using bgeu instead in the preceding check?

The syscall number could be -1 if tracer rejected it.

We could do:

li t0, __NR_syscalls
[..]
// first check if syscall was rejected
li t1, -1
beq a7, t1, ret_from_syscall_rejected
// then check the bounds
bgeu a7, t0, 1f

>
>         /*
>          * Syscall number held in a7.
>          * If syscall number is above allowed value, redirect to ni_syscall.
>          */
>         bge a7, t0, 1f
>
> Andreas.
>
> --
> Andreas Schwab, SUSE Labs, schwab@xxxxxxx
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