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

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Message-ID: <mvmk16t53bl.fsf@suse.de>
Date:   Wed, 18 Dec 2019 11:35:26 +0100
From:   Andreas Schwab <schwab@...e.de>
To:     David Abdurachmanov <david.abdurachmanov@...il.com>
Cc:     Paul Walmsley <paul.walmsley@...ive.com>,
        Palmer Dabbelt <palmer@...belt.com>,
        Albert Ou <aou@...s.berkeley.edu>,
        David Abdurachmanov <david.abdurachmanov@...ive.com>,
        Kees Cook <keescook@...omium.org>,
        Anup Patel <Anup.Patel@....com>,
        Vincent Chen <vincent.chen@...ive.com>,
        Valentin Schneider <valentin.schneider@....com>,
        Thomas Gleixner <tglx@...utronix.de>,
        Bin Meng <bmeng.cn@...il.com>,
        linux-riscv <linux-riscv@...ts.infradead.org>,
        "linux-kernel\@vger.kernel.org List" <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH] riscv: reject invalid syscalls below -1

On Dez 18 2019, David Abdurachmanov wrote:

> On Wed, Dec 18, 2019 at 11:46 AM Andreas Schwab <schwab@...e.de> 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.

So check for -1 first, then for out-of-range?

Andreas.

-- 
Andreas Schwab, SUSE Labs, schwab@...e.de
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