linux-kernel - Re: [PATCH v3 18/26] arm64: Introduce asm/vdso/processor.h

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Date:   Mon, 16 Mar 2020 16:05:17 +0000
From:   Vincenzo Frascino <vincenzo.frascino@....com>
To:     Catalin Marinas <catalin.marinas@....com>
Cc:     linux-arch@...r.kernel.org, linux-arm-kernel@...ts.infradead.org,
        linux-kernel@...r.kernel.org, linux-mips@...r.kernel.org,
        clang-built-linux@...glegroups.com, x86@...nel.org,
        Will Deacon <will.deacon@....com>,
        Arnd Bergmann <arnd@...db.de>,
        Russell King <linux@...linux.org.uk>,
        Paul Burton <paul.burton@...s.com>,
        Thomas Gleixner <tglx@...utronix.de>,
        Andy Lutomirski <luto@...nel.org>,
        Ingo Molnar <mingo@...hat.com>, Borislav Petkov <bp@...en8.de>,
        Stephen Boyd <sboyd@...nel.org>,
        Mark Salyzyn <salyzyn@...roid.com>,
        Kees Cook <keescook@...omium.org>,
        Peter Collingbourne <pcc@...gle.com>,
        Dmitry Safonov <0x7f454c46@...il.com>,
        Andrei Vagin <avagin@...nvz.org>,
        Nick Desaulniers <ndesaulniers@...gle.com>,
        Marc Zyngier <maz@...nel.org>,
        Mark Rutland <Mark.Rutland@....com>,
        Will Deacon <will@...nel.org>
Subject: Re: [PATCH v3 18/26] arm64: Introduce asm/vdso/processor.h

On 3/16/20 3:49 PM, Catalin Marinas wrote:
> On Mon, Mar 16, 2020 at 03:33:30PM +0000, Vincenzo Frascino wrote:
>> On 3/16/20 2:43 PM, Catalin Marinas wrote[...]
[...]
> 
>> To make it more explicit we could make COMPAT_VDSO on arm64 depend on
>> ARM64_4K_PAGES. What do you think?
> 
> No, I don't see why we should add this limitation.
> 

Fine by me.

>>>> Please find below the list of errors for clock_gettime (similar for the other):
>>>>
>>>> passing UINTPTR_MAX to clock_gettime (VDSO): terminated by unexpected signal 7
>>>> clock-gettime-monotonic/abi: 1 failures/inconsistencies encountered
>>>
>>> Ah, so it uses UINTPTR_MAX in the test. Fair enough but I don't think
>>> the arm64 check is entirely useful. On arm32, the check was meant to
>>> return -EFAULT for addresses beyond TASK_SIZE that may enter into the
>>> kernel or module space. On arm64 compat, the kernel space is well above
>>> the reach of the 32-bit code.
>>>
>>> If you want to preserve some compatibility for this specific test, what
>>> about checking for wrapping around 0, I think it would make more sense.
>>> Something like:
>>>
>>> 	if ((u32)ts > UINTPTR_MAX - sizeof(*ts) + 1)
>>
>> Ok, sounds good to me. But it is something that this patch series inherited,
>> hence I would prefer to send a separate patch that introduces what you are
>> proposing and removes TASK_SIZE_32 from the headers. How does it sound?
> 
> I'd rather avoid moving TASK_SIZE_32 unnecessarily. Just add a
> preparatory patch to your series for arm64 compat vdso and follow with
> the rest without moving TASK_SIZE_32 around.
> 

Ok, sounds good. I will test it and repost.

-- 
Regards,
Vincenzo