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From: Linus Torvalds <torvalds@linux-foundation.org>
To: Andrey Konovalov <andreyknvl@google.com>
Cc: Catalin Marinas <catalin.marinas@arm.com>,
	Will Deacon <will.deacon@arm.com>,
	Mark Rutland <mark.rutland@arm.com>,
	Robin Murphy <robin.murphy@arm.com>,
	Al Viro <viro@zeniv.linux.org.uk>,
	Kees Cook <keescook@chromium.org>,
	Kate Stewart <kstewart@linuxfoundation.org>,
	Greg Kroah-Hartman <gregkh@linuxfoundation.org>,
	Andrew Morton <akpm@linux-foundation.org>,
	Ingo Molnar <mingo@kernel.org>,
	"Kirill A. Shutemov" <kirill.shutemov@linux.intel.com>,
	Shuah Khan <shuah@kernel.org>,
	linux-arm-kernel <linux-arm-kernel@lists.infradead.org>,
	"open list:DOCUMENTATION" <linux-doc@vger.kernel.org>,
	linux-mm <linux-mm@kvack.org>,
	linux-arch <linux-arch@vger.kernel.org>,
	"open list:KERNEL SELFTEST FRAMEWORK" 
	<linux-kselftest@vger.kernel.org>,
	Linux Kernel Mailing List <linux-kernel@vger.kernel.org>,
	Dmitry Vyukov <dvyukov@google.com>,
	Kostya Serebryany <kcc@google.com>,
	eugenis@google.com, Lee.Smith@arm.com,
	Ramana Radhakrishnan <Ramana.Radhakrishnan@arm.com>,
	Jacob.Bramley@arm.com, Ruben.Ayrapetyan@arm.com,
	cpandya@codeaurora.org
Subject: Re: [PATCH v6 11/11] arm64: annotate user pointers casts detected by sparse
Date: Thu, 6 Sep 2018 14:13:41 -0700	[thread overview]
Message-ID: <CA+55aFyW9N2tSb2bQvkthbVVyY6nt5yFeWQRLHp1zruBmb5ocw@mail.gmail.com> (raw)
In-Reply-To: <5d54526e5ff2e5ad63d0dfdd9ab17cf359afa4f2.1535629099.git.andreyknvl@google.com>

On Thu, Aug 30, 2018 at 4:41 AM Andrey Konovalov <andreyknvl@google.com> wrote:
>
> This patch adds __force annotations for __user pointers casts detected by
> sparse with the -Wcast-from-as flag enabled (added in [1]).

No, several of these are wrong, and just silence a warning that shows a problem.

So for example:

>  static inline compat_uptr_t ptr_to_compat(void __user *uptr)
>  {
> -       return (u32)(unsigned long)uptr;
> +       return (u32)(__force unsigned long)uptr;
>  }

this actually looks correct.

But:

> --- a/arch/arm64/include/asm/uaccess.h
> +++ b/arch/arm64/include/asm/uaccess.h
> @@ -76,7 +76,7 @@ static inline unsigned long __range_ok(const void __user *addr, unsigned long si
>  {
>         unsigned long ret, limit = current_thread_info()->addr_limit;
>
> -       __chk_user_ptr(addr);
> +       __chk_user_ptr((void __force *)addr);

This looks actively wrong. The whole - and only - point of
"__chk_user_ptr()" is that it warns about a lack of a "__user *" type.

So the above makes no sense at all.

There are other similar "that makes no sense what-so-ever", like this one:

> -               struct compat_group_req __user *gr32 = (void *)optval;
> +               struct compat_group_req __user *gr32 = (__force void *)optval;

no, the additionl of __force is not the right thing, the problem, is
that a __user pointer is cast to a non-user 'void *' only to be
assigned to another user type.

The fix should have been to use (void __user *) as the cast instead,
no __force needed.

In general, I think the patch shows all the signs of "mindlessly just
add casts", which is exactly the wrong thing to do to sparse warnings.

                   Linus

  parent reply	other threads:[~2018-09-06 21:13 UTC|newest]

Thread overview: 34+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2018-08-30 11:41 [PATCH v6 00/11] arm64: untag user pointers passed to the kernel Andrey Konovalov
2018-08-30 11:41 ` [PATCH v6 01/11] arm64: add type casts to untagged_addr macro Andrey Konovalov
2018-08-30 11:41 ` [PATCH v6 02/11] uaccess: add untagged_addr definition for other arches Andrey Konovalov
2018-08-30 11:41 ` [PATCH v6 03/11] arm64: untag user addresses in access_ok and __uaccess_mask_ptr Andrey Konovalov
2018-08-30 11:41 ` [PATCH v6 04/11] mm, arm64: untag user addresses in mm/gup.c Andrey Konovalov
2018-08-30 11:41 ` [PATCH v6 05/11] lib, arm64: untag addrs passed to strncpy_from_user and strnlen_user Andrey Konovalov
2018-08-30 11:41 ` [PATCH v6 06/11] arm64: untag user address in __do_user_fault Andrey Konovalov
2018-08-30 11:41 ` [PATCH v6 07/11] fs, arm64: untag user address in copy_mount_options Andrey Konovalov
2018-08-30 11:41 ` [PATCH v6 08/11] usb, arm64: untag user addresses in devio Andrey Konovalov
2018-08-30 11:41 ` [PATCH v6 09/11] arm64: update Documentation/arm64/tagged-pointers.txt Andrey Konovalov
2018-08-30 11:41 ` [PATCH v6 10/11] selftests, arm64: add a selftest for passing tagged pointers to kernel Andrey Konovalov
2018-08-30 11:41 ` [PATCH v6 11/11] arm64: annotate user pointers casts detected by sparse Andrey Konovalov
2018-08-31  8:11   ` Luc Van Oostenryck
2018-08-31 13:42     ` Al Viro
2018-09-03 12:34       ` Andrey Konovalov
2018-09-03 13:49         ` Vincenzo Frascino
2018-09-03 15:10           ` Luc Van Oostenryck
2018-09-04 11:27             ` Vincenzo Frascino
2018-09-05 19:03               ` Luc Van Oostenryck
2018-09-06 14:13                 ` Vincenzo Frascino
2018-09-06 20:10                   ` Luc Van Oostenryck
2018-09-03 13:56         ` Al Viro
2018-09-06 21:13   ` Linus Torvalds [this message]
2018-09-06 21:16     ` Linus Torvalds
2018-09-06 23:08       ` Luc Van Oostenryck
2018-09-07 15:26       ` Catalin Marinas
2018-09-07 16:30         ` Linus Torvalds
2018-09-11 16:41           ` Catalin Marinas
2018-09-17 17:01             ` Andrey Konovalov
2018-09-24 15:04               ` Andrey Konovalov
2018-09-28 17:50               ` Catalin Marinas
2018-10-02 13:19                 ` Andrey Konovalov
2018-09-14  1:25   ` [LKP] [arm64] 7b5b51e7b3: kvm-unit-tests.rmap_chain.fail kernel test robot
2018-08-30 11:48 ` [PATCH v6 00/11] arm64: untag user pointers passed to the kernel Andrey Konovalov

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