linux-kernel - Re: [RFC UKL 05/10] x86/uaccess: Make access

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Message-Id: <d32399c1-88ae-4b7d-925e-b82b2a983e30@app.fastmail.com>
Date:   Tue, 04 Oct 2022 10:36:38 -0700
From:   "Andy Lutomirski" <luto@...nel.org>
To:     "Ali Raza" <aliraza@...edu>,
        "Linux Kernel Mailing List" <linux-kernel@...r.kernel.org>
Cc:     "Jonathan Corbet" <corbet@....net>, masahiroy@...nel.org,
        michal.lkml@...kovi.net,
        "Nick Desaulniers" <ndesaulniers@...gle.com>,
        "Thomas Gleixner" <tglx@...utronix.de>,
        "Ingo Molnar" <mingo@...hat.com>, "Borislav Petkov" <bp@...en8.de>,
        "Dave Hansen" <dave.hansen@...ux.intel.com>,
        "H. Peter Anvin" <hpa@...or.com>,
        "Eric W. Biederman" <ebiederm@...ssion.com>,
        "Kees Cook" <keescook@...omium.org>,
        "Peter Zijlstra (Intel)" <peterz@...radead.org>,
        "Al Viro" <viro@...iv.linux.org.uk>,
        "Arnd Bergmann" <arnd@...db.de>, juri.lelli@...hat.com,
        vincent.guittot@...aro.org, dietmar.eggemann@....com,
        "Steven Rostedt" <rostedt@...dmis.org>,
        "Ben Segall" <bsegall@...gle.com>, mgorman@...e.de,
        bristot@...hat.com, vschneid@...hat.com,
        "Paolo Bonzini" <pbonzini@...hat.com>, jpoimboe@...nel.org,
        linux-doc@...r.kernel.org, linux-kbuild@...r.kernel.org,
        linux-mm@...ck.org, linux-fsdevel@...r.kernel.org,
        linux-arch@...r.kernel.org,
        "the arch/x86 maintainers" <x86@...nel.org>, rjones@...hat.com,
        munsoner@...edu, tommyu@...edu, drepper@...hat.com,
        lwoodman@...hat.com, mboydmcse@...il.com, okrieg@...edu,
        rmancuso@...edu
Subject: Re: [RFC UKL 05/10] x86/uaccess: Make access_ok UKL aware



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@....net>
> Cc: Masahiro Yamada <masahiroy@...nel.org>
> Cc: Michal Marek <michal.lkml@...kovi.net>
> Cc: Nick Desaulniers <ndesaulniers@...gle.com>
> Cc: Thomas Gleixner <tglx@...utronix.de>
> Cc: Ingo Molnar <mingo@...hat.com>
> Cc: Borislav Petkov <bp@...en8.de>
> Cc: Dave Hansen <dave.hansen@...ux.intel.com>
> Cc: "H. Peter Anvin" <hpa@...or.com>
> Cc: Andy Lutomirski <luto@...nel.org>
> Cc: Eric Biederman <ebiederm@...ssion.com>
> Cc: Kees Cook <keescook@...omium.org>
> Cc: Peter Zijlstra <peterz@...radead.org>
> Cc: Alexander Viro <viro@...iv.linux.org.uk>
> Cc: Arnd Bergmann <arnd@...db.de>
> Cc: Juri Lelli <juri.lelli@...hat.com>
> Cc: Vincent Guittot <vincent.guittot@...aro.org>
> Cc: Dietmar Eggemann <dietmar.eggemann@....com>
> Cc: Steven Rostedt <rostedt@...dmis.org>
> Cc: Ben Segall <bsegall@...gle.com>
> Cc: Mel Gorman <mgorman@...e.de>
> Cc: Daniel Bristot de Oliveira <bristot@...hat.com>
> Cc: Valentin Schneider <vschneid@...hat.com>
> Cc: Paolo Bonzini <pbonzini@...hat.com>
> Cc: Josh Poimboeuf <jpoimboe@...nel.org>
>
> Signed-off-by: Ali Raza <aliraza@...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