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From: Andrey Konovalov <andreyknvl@google.com>
To: Catalin Marinas <catalin.marinas@arm.com>
Cc: Will Deacon <will.deacon@arm.com>,
	Jonathan Corbet <corbet@lwn.net>,
	Mark Rutland <mark.rutland@arm.com>,
	Robin Murphy <robin.murphy@arm.com>,
	Al Viro <viro@zeniv.linux.org.uk>,
	James Morse <james.morse@arm.com>,
	Kees Cook <keescook@chromium.org>,
	Bart Van Assche <bart.vanassche@wdc.com>,
	Kate Stewart <kstewart@linuxfoundation.org>,
	Greg Kroah-Hartman <gregkh@linuxfoundation.org>,
	Thomas Gleixner <tglx@linutronix.de>,
	Philippe Ombredanne <pombredanne@nexb.com>,
	Andrew Morton <akpm@linux-foundation.org>,
	Ingo Molnar <mingo@kernel.org>,
	"Kirill A . Shutemov" <kirill.shutemov@linux.intel.com>,
	Dan Williams <dan.j.williams@intel.com>,
	"Aneesh Kumar K . V" <aneesh.kumar@linux.vnet.ibm.com>,
	Zi Yan <zi.yan@cs.rutgers.edu>,
	Linux ARM <linux-arm-kernel@lists.infradead.org>,
	linux-doc@vger.kernel.org, LKML <linux-kernel@vger.kernel.org>,
	Linux Memory Management List <linux-mm@kvack.org>,
	Jacob Bramley <Jacob.Bramley@arm.com>,
	Ruben Ayrapetyan <Ruben.Ayrapetyan@arm.com>,
	Lee Smith <Lee.Smith@arm.com>, Kostya Serebryany <kcc@google.com>,
	Dmitry Vyukov <dvyukov@google.com>,
	Ramana Radhakrishnan <Ramana.Radhakrishnan@arm.com>,
	Evgeniy Stepanov <eugenis@google.com>
Subject: Re: [PATCH 3/6] arm64: untag user addresses in copy_from_user and others
Date: Wed, 2 May 2018 17:29:04 +0200	[thread overview]
Message-ID: <CAAeHK+xWV2RNuoOrgkLrQ973eV2r8xFOcrzHWVrQZz7XA2WGYA@mail.gmail.com> (raw)
In-Reply-To: <20180426154725.74a33tnevvbtqx63@armageddon.cambridge.arm.com>

On Thu, Apr 26, 2018 at 5:47 PM, Catalin Marinas
<catalin.marinas@arm.com> wrote:
> On Wed, Apr 18, 2018 at 08:53:12PM +0200, Andrey Konovalov wrote:
>> @@ -238,12 +239,15 @@ static inline void uaccess_enable_not_uao(void)
>>  /*
>>   * Sanitise a uaccess pointer such that it becomes NULL if above the
>>   * current addr_limit.
>> + * Also untag user pointers that have the top byte tag set.
>>   */
>>  #define uaccess_mask_ptr(ptr) (__typeof__(ptr))__uaccess_mask_ptr(ptr)
>>  static inline void __user *__uaccess_mask_ptr(const void __user *ptr)
>>  {
>>       void __user *safe_ptr;
>>
>> +     ptr = untagged_addr(ptr);
>> +
>>       asm volatile(
>>       "       bics    xzr, %1, %2\n"
>>       "       csel    %0, %1, xzr, eq\n"
>
> First of all, passing a tagged user pointer throughout the kernel is
> safe with uaccess routines but not suitable for find_vma() etc.
>
> With this change, we may have an inconsistent behaviour on the tag
> masking, depending on whether the entry code uses __uaccess_mask_ptr()
> or not. We could preserve the tag with something like:
>
> diff --git a/arch/arm64/include/asm/uaccess.h b/arch/arm64/include/asm/uaccess.h
> index e66b0fca99c2..ed15bfcbd797 100644
> --- a/arch/arm64/include/asm/uaccess.h
> +++ b/arch/arm64/include/asm/uaccess.h
> @@ -244,10 +244,11 @@ static inline void __user *__uaccess_mask_ptr(const void __user *ptr)
>         void __user *safe_ptr;
>
>         asm volatile(
> -       "       bics    xzr, %1, %2\n"
> +       "       bics    xzr, %3, %2\n"
>         "       csel    %0, %1, xzr, eq\n"
>         : "=&r" (safe_ptr)
> -       : "r" (ptr), "r" (current_thread_info()->addr_limit)
> +       : "r" (ptr), "r" (current_thread_info()->addr_limit),
> +         "r" (untagged_addr(ptr))
>         : "cc");
>
>         csdb();

Just to make sure I understood this assembly snippet correctly, this
change will result in checking untagged address against addr_limit,
and returning the original tagged address if the check passes. Sure,
sounds good, I'll do that.

  reply	other threads:[~2018-05-02 15:29 UTC|newest]

Thread overview: 21+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2018-04-18 18:53 [PATCH 0/6] arm64: untag user pointers passed to the kernel Andrey Konovalov
2018-04-18 18:53 ` [PATCH 1/6] arm64: add type casts to untagged_addr macro Andrey Konovalov
2018-04-18 18:53 ` [PATCH 2/6] uaccess: add untagged_addr definition for other arches Andrey Konovalov
2018-04-18 18:53 ` [PATCH 3/6] arm64: untag user addresses in copy_from_user and others Andrey Konovalov
2018-04-26 15:47   ` Catalin Marinas
2018-05-02 15:29     ` Andrey Konovalov [this message]
2018-04-18 18:53 ` [PATCH 4/6] mm, arm64: untag user addresses in mm/gup.c Andrey Konovalov
2018-04-26 17:47   ` Catalin Marinas
2018-05-02 14:38     ` Andrey Konovalov
2018-05-02 15:36       ` Kirill A. Shutemov
2018-05-02 17:25         ` Andrey Konovalov
2018-05-03 14:09           ` Andrey Konovalov
2018-05-03 15:24             ` Kirill A. Shutemov
2018-05-03 16:51               ` Andrey Konovalov
2018-05-08 15:11           ` Catalin Marinas
2018-05-11 12:36             ` Andrey Konovalov
2018-04-18 18:53 ` [PATCH 5/6] lib, arm64: untag addrs passed to strncpy_from_user and strnlen_user Andrey Konovalov
2018-04-18 18:53 ` [PATCH 6/6] arm64: update Documentation/arm64/tagged-pointers.txt Andrey Konovalov
2018-04-19  9:33 ` [PATCH 0/6] arm64: untag user pointers passed to the kernel Kirill A. Shutemov
2018-04-25 14:45   ` Andrey Konovalov
2018-04-26 17:56     ` Catalin Marinas

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