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Date:   Tue, 04 Oct 2022 10:36:38 -0700
From:   "Andy Lutomirski" <luto@kernel.org>
To:     "Ali Raza" <aliraza@bu.edu>,
        "Linux Kernel Mailing List" <linux-kernel@vger.kernel.org>
Cc:     "Jonathan Corbet" <corbet@lwn.net>, masahiroy@kernel.org,
        michal.lkml@markovi.net,
        "Nick Desaulniers" <ndesaulniers@google.com>,
        "Thomas Gleixner" <tglx@linutronix.de>,
        "Ingo Molnar" <mingo@redhat.com>, "Borislav Petkov" <bp@alien8.de>,
        "Dave Hansen" <dave.hansen@linux.intel.com>,
        "H. Peter Anvin" <hpa@zytor.com>,
        "Eric W. Biederman" <ebiederm@xmission.com>,
        "Kees Cook" <keescook@chromium.org>,
        "Peter Zijlstra (Intel)" <peterz@infradead.org>,
        "Al Viro" <viro@zeniv.linux.org.uk>,
        "Arnd Bergmann" <arnd@arndb.de>, juri.lelli@redhat.com,
        vincent.guittot@linaro.org, dietmar.eggemann@arm.com,
        "Steven Rostedt" <rostedt@goodmis.org>,
        "Ben Segall" <bsegall@google.com>, mgorman@suse.de,
        bristot@redhat.com, vschneid@redhat.com,
        "Paolo Bonzini" <pbonzini@redhat.com>, jpoimboe@kernel.org,
        linux-doc@vger.kernel.org, linux-kbuild@vger.kernel.org,
        linux-mm@kvack.org, linux-fsdevel@vger.kernel.org,
        linux-arch@vger.kernel.org,
        "the arch/x86 maintainers" <x86@kernel.org>, rjones@redhat.com,
        munsoner@bu.edu, tommyu@bu.edu, drepper@redhat.com,
        lwoodman@redhat.com, mboydmcse@gmail.com, okrieg@bu.edu,
        rmancuso@bu.edu
Subject: Re: [RFC UKL 05/10] x86/uaccess: Make access_ok UKL aware
Content-Type: text/plain
Precedence: bulk


On Mon, Oct 3, 2022, at 3:21 PM, Ali Raza wrote:
> When configured for UKL, access_ok needs to account for the unified address
> space that is used by the kernel and the process being run. To do this,
> they need to check the task struct field added earlier to determine where
> the execution that is making the check is running. For a zero value, the
> normal boundary definitions apply, but non-zero value indicates a UKL
> thread and a shared address space should be assumed.

I think this is just wrong.  Why should a UKL process be able to read() to kernel (high-half) memory?

set_fs() is gone.  Please keep it gone.

>
> Cc: Jonathan Corbet <corbet@lwn.net>
> Cc: Masahiro Yamada <masahiroy@kernel.org>
> Cc: Michal Marek <michal.lkml@markovi.net>
> Cc: Nick Desaulniers <ndesaulniers@google.com>
> Cc: Thomas Gleixner <tglx@linutronix.de>
> Cc: Ingo Molnar <mingo@redhat.com>
> Cc: Borislav Petkov <bp@alien8.de>
> Cc: Dave Hansen <dave.hansen@linux.intel.com>
> Cc: "H. Peter Anvin" <hpa@zytor.com>
> Cc: Andy Lutomirski <luto@kernel.org>
> Cc: Eric Biederman <ebiederm@xmission.com>
> Cc: Kees Cook <keescook@chromium.org>
> Cc: Peter Zijlstra <peterz@infradead.org>
> Cc: Alexander Viro <viro@zeniv.linux.org.uk>
> Cc: Arnd Bergmann <arnd@arndb.de>
> Cc: Juri Lelli <juri.lelli@redhat.com>
> Cc: Vincent Guittot <vincent.guittot@linaro.org>
> Cc: Dietmar Eggemann <dietmar.eggemann@arm.com>
> Cc: Steven Rostedt <rostedt@goodmis.org>
> Cc: Ben Segall <bsegall@google.com>
> Cc: Mel Gorman <mgorman@suse.de>
> Cc: Daniel Bristot de Oliveira <bristot@redhat.com>
> Cc: Valentin Schneider <vschneid@redhat.com>
> Cc: Paolo Bonzini <pbonzini@redhat.com>
> Cc: Josh Poimboeuf <jpoimboe@kernel.org>
>
> Signed-off-by: Ali Raza <aliraza@bu.edu>
> ---
>  arch/x86/include/asm/uaccess.h | 8 ++++++++
>  1 file changed, 8 insertions(+)
>
> diff --git a/arch/x86/include/asm/uaccess.h b/arch/x86/include/asm/uaccess.h
> index 913e593a3b45..adef521b2e59 100644
> --- a/arch/x86/include/asm/uaccess.h
> +++ b/arch/x86/include/asm/uaccess.h
> @@ -37,11 +37,19 @@ static inline bool pagefault_disabled(void);
>   * Return: true (nonzero) if the memory block may be valid, false (zero)
>   * if it is definitely invalid.
>   */
> +#ifdef CONFIG_UNIKERNEL_LINUX
> +#define access_ok(addr, size)					\
> +({									\
> +	WARN_ON_IN_IRQ();						\
> +	(is_ukl_thread() ? 1 : likely(__access_ok(addr, size)));	\
> +})
> +#else
>  #define access_ok(addr, size)					\
>  ({									\
>  	WARN_ON_IN_IRQ();						\
>  	likely(__access_ok(addr, size));				\
>  })
> +#endif
> 
>  #include <asm-generic/access_ok.h>
> 
> -- 
> 2.21.3