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

From: Jules Maselbas <jmaselbas@kalray.eu>
To: "Jason A. Donenfeld" <Jason@zx2c4.com>
Cc: "Yann Sionneau" <ysionneau@kalray.eu>,
	"Arnd Bergmann" <arnd@arndb.de>,
	"Jonathan Corbet" <corbet@lwn.net>,
	"Thomas Gleixner" <tglx@linutronix.de>,
	"Marc Zyngier" <maz@kernel.org>,
	"Rob Herring" <robh+dt@kernel.org>,
	"Krzysztof Kozlowski" <krzysztof.kozlowski+dt@linaro.org>,
	"Will Deacon" <will@kernel.org>,
	"Peter Zijlstra" <peterz@infradead.org>,
	"Boqun Feng" <boqun.feng@gmail.com>,
	"Mark Rutland" <mark.rutland@arm.com>,
	"Eric Biederman" <ebiederm@xmission.com>,
	"Kees Cook" <keescook@chromium.org>,
	"Oleg Nesterov" <oleg@redhat.com>,
	"Ingo Molnar" <mingo@redhat.com>,
	"Waiman Long" <longman@redhat.com>,
	"Aneesh Kumar K.V" <aneesh.kumar@linux.ibm.com>,
	"Andrew Morton" <akpm@linux-foundation.org>,
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Subject: Re: [RFC PATCH v2 12/31] kvx: Add other common headers
Date: Wed, 25 Jan 2023 22:55:19 +0100	[thread overview]
Message-ID: <20230125215519.GE5952@tellis.lin.mbt.kalray.eu> (raw)
In-Reply-To: <Y8qlOpYgDefMPqWH@zx2c4.com>

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

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