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

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Message-ID: <mvmo8w63r1d.fsf@suse.de>
Date:   Wed, 18 Dec 2019 10:46:06 +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@...ts.infradead.org,
        linux-kernel@...r.kernel.org
Subject: Re: [PATCH] riscv: reject invalid syscalls below -1

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?

	/*
	 * 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@...e.de
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