linux-kernel - Re: [RFC PATCH v2 12/31] kvx: Add other common headers

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Message-ID: <Y8qlOpYgDefMPqWH@zx2c4.com>
Date:   Fri, 20 Jan 2023 15:29:14 +0100
From:   "Jason A. Donenfeld" <Jason@...c4.com>
To:     Yann Sionneau <ysionneau@...ray.eu>
Cc:     Arnd Bergmann <arnd@...db.de>, Jonathan Corbet <corbet@....net>,
        Thomas Gleixner <tglx@...utronix.de>,
        Marc Zyngier <maz@...nel.org>,
        Rob Herring <robh+dt@...nel.org>,
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        Waiman Long <longman@...hat.com>,
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Subject: Re: [RFC PATCH v2 12/31] kvx: Add other common headers

Hi Yann,

On Fri, Jan 20, 2023 at 03:09:43PM +0100, Yann Sionneau wrote:
> +#include <linux/random.h>
> +#include <linux/version.h>
> +
> +extern unsigned long __stack_chk_guard;
> +
> +/*
> + * Initialize the stackprotector canary value.
> + *
> + * NOTE: this must only be called from functions that never return,
> + * and it must always be inlined.
> + */
> +static __always_inline void boot_init_stack_canary(void)
> +{
> +	unsigned long canary;
> +
> +	/* Try to get a semi random initial value. */
> +	get_random_bytes(&canary, sizeof(canary));
> +	canary ^= LINUX_VERSION_CODE;
> +	canary &= CANARY_MASK;
> +
> +	current->stack_canary = canary;
> +	__stack_chk_guard = current->stack_canary;
> +}


You should rewrite this as:

    current->stack_canary = get_random_canary();
    __stack_chk_guard = current->stack_canary;

which is what the other archs all now do. (They didn't used to, and this
looks like it's simply based on older code.)

> +#define get_cycles get_cycles
> +
> +#include <asm/sfr.h>
> +#include <asm-generic/timex.h>
> +
> +static inline cycles_t get_cycles(void)
> +{
> +	return kvx_sfr_get(PM0);
> +}

Glad to see this CPU has a cycle counter. Out of curiosity, what is
its resolution?

Also, related, does this CPU happen to have a "RDRAND"-like instruction?
(I don't know anything about kvx or even what it is.)

Jason