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

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Date:   Wed, 25 Jan 2023 22:55:19 +0100
From:   Jules Maselbas <jmaselbas@...ray.eu>
To:     "Jason A. Donenfeld" <Jason@...c4.com>
Cc:     Yann Sionneau <ysionneau@...ray.eu>, 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>,
        Krzysztof Kozlowski <krzysztof.kozlowski+dt@...aro.org>,
        Will Deacon <will@...nel.org>,
        Peter Zijlstra <peterz@...radead.org>,
        Boqun Feng <boqun.feng@...il.com>,
        Mark Rutland <mark.rutland@....com>,
        Eric Biederman <ebiederm@...ssion.com>,
        Kees Cook <keescook@...omium.org>,
        Oleg Nesterov <oleg@...hat.com>,
        Ingo Molnar <mingo@...hat.com>,
        Waiman Long <longman@...hat.com>,
        "Aneesh Kumar K.V" <aneesh.kumar@...ux.ibm.com>,
        Andrew Morton <akpm@...ux-foundation.org>,
        Nick Piggin <npiggin@...il.com>,
        Paul Moore <paul@...l-moore.com>,
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Subject: Re: [RFC PATCH v2 12/31] kvx: Add other common headers

Hi Jason,

On Fri, Jan 20, 2023 at 03:29:14PM +0100, Jason A. Donenfeld wrote:
> 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.)
Thanks for the suggestion, this will be into v3

> > +#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?
This cpu has 4 performance monitor (PM), the first one is reserved to
count cycles, and it is cycle accurate.

> Also, related, does this CPU happen to have a "RDRAND"-like instruction?
I didn't knew about the RDRAND insruction, but no this CPU do not have
an instruction like that.

> (I don't know anything about kvx or even what it is.)
It's a VLIW core, a bit like Itanium, there are currently not publicly
available documentation.  We have started a discussion internally at
Kalray to share more information regarding this CPU and its ABI.

A very crude instruction listing can be found in our fork of
gdb-binutils: https://raw.githubusercontent.com/kalray/binutils/binutils-2_35_2/coolidge/opcodes/kv3-opc.c

Best regards,
-- Jules