linux-kernel - Re: [PATCH v11 09/14] kernel, arm64: untag user pointers in prctl_set

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Date:   Mon, 18 Mar 2019 11:47:15 +0000
From:   Kevin Brodsky <kevin.brodsky@....com>
To:     Andrey Konovalov <andreyknvl@...gle.com>,
        Catalin Marinas <catalin.marinas@....com>,
        Will Deacon <will.deacon@....com>,
        Mark Rutland <mark.rutland@....com>,
        Robin Murphy <robin.murphy@....com>,
        Kees Cook <keescook@...omium.org>,
        Kate Stewart <kstewart@...uxfoundation.org>,
        Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
        Andrew Morton <akpm@...ux-foundation.org>,
        Ingo Molnar <mingo@...nel.org>,
        "Kirill A . Shutemov" <kirill.shutemov@...ux.intel.com>,
        Shuah Khan <shuah@...nel.org>,
        Vincenzo Frascino <vincenzo.frascino@....com>,
        Eric Dumazet <edumazet@...gle.com>,
        "David S. Miller" <davem@...emloft.net>,
        Alexei Starovoitov <ast@...nel.org>,
        Daniel Borkmann <daniel@...earbox.net>,
        Steven Rostedt <rostedt@...dmis.org>,
        Ingo Molnar <mingo@...hat.com>,
        Peter Zijlstra <peterz@...radead.org>,
        Arnaldo Carvalho de Melo <acme@...nel.org>,
        linux-arm-kernel@...ts.infradead.org, linux-doc@...r.kernel.org,
        linux-mm@...ck.org, linux-arch@...r.kernel.org,
        netdev@...r.kernel.org, bpf@...r.kernel.org,
        linux-kselftest@...r.kernel.org, linux-kernel@...r.kernel.org
Cc:     Dmitry Vyukov <dvyukov@...gle.com>,
        Kostya Serebryany <kcc@...gle.com>,
        Evgeniy Stepanov <eugenis@...gle.com>,
        Lee Smith <Lee.Smith@....com>,
        Ramana Radhakrishnan <Ramana.Radhakrishnan@....com>,
        Jacob Bramley <Jacob.Bramley@....com>,
        Ruben Ayrapetyan <Ruben.Ayrapetyan@....com>,
        Chintan Pandya <cpandya@...eaurora.org>,
        Luc Van Oostenryck <luc.vanoostenryck@...il.com>,
        Dave Martin <Dave.Martin@....com>,
        Szabolcs Nagy <Szabolcs.Nagy@....com>
Subject: Re: [PATCH v11 09/14] kernel, arm64: untag user pointers in
 prctl_set_mm*

On 15/03/2019 19:51, Andrey Konovalov wrote:
> This patch is a part of a series that extends arm64 kernel ABI to allow to
> pass tagged user pointers (with the top byte set to something else other
> than 0x00) as syscall arguments.
>
> prctl_set_mm() and prctl_set_mm_map() use provided user pointers for vma
> lookups, which can only by done with untagged pointers.
>
> Untag user pointers in these functions.
>
> Signed-off-by: Andrey Konovalov <andreyknvl@...gle.com>
> ---
>   kernel/sys.c | 14 ++++++++++++++
>   1 file changed, 14 insertions(+)
>
> diff --git a/kernel/sys.c b/kernel/sys.c
> index 12df0e5434b8..8e56d87cc6db 100644
> --- a/kernel/sys.c
> +++ b/kernel/sys.c
> @@ -1993,6 +1993,18 @@ static int prctl_set_mm_map(int opt, const void __user *addr, unsigned long data
>   	if (copy_from_user(&prctl_map, addr, sizeof(prctl_map)))
>   		return -EFAULT;
>   
> +	prctl_map->start_code	= untagged_addr(prctl_map.start_code);
> +	prctl_map->end_code	= untagged_addr(prctl_map.end_code);
> +	prctl_map->start_data	= untagged_addr(prctl_map.start_data);
> +	prctl_map->end_data	= untagged_addr(prctl_map.end_data);
> +	prctl_map->start_brk	= untagged_addr(prctl_map.start_brk);
> +	prctl_map->brk		= untagged_addr(prctl_map.brk);
> +	prctl_map->start_stack	= untagged_addr(prctl_map.start_stack);
> +	prctl_map->arg_start	= untagged_addr(prctl_map.arg_start);
> +	prctl_map->arg_end	= untagged_addr(prctl_map.arg_end);
> +	prctl_map->env_start	= untagged_addr(prctl_map.env_start);
> +	prctl_map->env_end	= untagged_addr(prctl_map.env_end);

As the buildbot suggests, those -> should be . instead :) You might want to check 
your local build with CONFIG_CHECKPOINT_RESTORE=y.

> +
>   	error = validate_prctl_map(&prctl_map);
>   	if (error)
>   		return error;
> @@ -2106,6 +2118,8 @@ static int prctl_set_mm(int opt, unsigned long addr,
>   			      opt != PR_SET_MM_MAP_SIZE)))
>   		return -EINVAL;
>   
> +	addr = untagged_addr(addr);

This is a bit too coarse, addr is indeed used for find_vma() later on, but it is also 
used to access memory, by prctl_set_mm_mmap() and prctl_set_auxv().

Kevin

> +
>   #ifdef CONFIG_CHECKPOINT_RESTORE
>   	if (opt == PR_SET_MM_MAP || opt == PR_SET_MM_MAP_SIZE)
>   		return prctl_set_mm_map(opt, (const void __user *)addr, arg4);