linux-kernel - Re: [RFC PATCH v4 4/9] mm/mmap: Add IBT bitmap size to address space limit check

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Date:   Wed, 3 Oct 2018 22:21:46 +0200
From:   Eugene Syromiatnikov <esyr@...hat.com>
To:     Yu-cheng Yu <yu-cheng.yu@...el.com>
Cc:     x86@...nel.org, "H. Peter Anvin" <hpa@...or.com>,
        Thomas Gleixner <tglx@...utronix.de>,
        Ingo Molnar <mingo@...hat.com>, linux-kernel@...r.kernel.org,
        linux-doc@...r.kernel.org, linux-mm@...ck.org,
        linux-arch@...r.kernel.org, linux-api@...r.kernel.org,
        Arnd Bergmann <arnd@...db.de>,
        Andy Lutomirski <luto@...capital.net>,
        Balbir Singh <bsingharora@...il.com>,
        Cyrill Gorcunov <gorcunov@...il.com>,
        Dave Hansen <dave.hansen@...ux.intel.com>,
        Florian Weimer <fweimer@...hat.com>,
        "H.J. Lu" <hjl.tools@...il.com>, Jann Horn <jannh@...gle.com>,
        Jonathan Corbet <corbet@....net>,
        Kees Cook <keescook@...omium.org>,
        Mike Kravetz <mike.kravetz@...cle.com>,
        Nadav Amit <nadav.amit@...il.com>,
        Oleg Nesterov <oleg@...hat.com>, Pavel Machek <pavel@....cz>,
        Peter Zijlstra <peterz@...radead.org>,
        Randy Dunlap <rdunlap@...radead.org>,
        "Ravi V. Shankar" <ravi.v.shankar@...el.com>,
        Vedvyas Shanbhogue <vedvyas.shanbhogue@...el.com>
Subject: Re: [RFC PATCH v4 4/9] mm/mmap: Add IBT bitmap size to address space
 limit check

On Fri, Sep 21, 2018 at 08:05:48AM -0700, Yu-cheng Yu wrote:
> The indirect branch tracking legacy bitmap takes a large address
> space.  This causes may_expand_vm() failure on the address limit
> check.  For a IBT-enabled task, add the bitmap size to the
> address limit.
> 
> Signed-off-by: Yu-cheng Yu <yu-cheng.yu@...el.com>
> ---
>  arch/x86/include/uapi/asm/resource.h |  5 +++++
>  include/uapi/asm-generic/resource.h  |  3 +++
>  mm/mmap.c                            | 12 +++++++++++-
>  3 files changed, 19 insertions(+), 1 deletion(-)
> 
> diff --git a/arch/x86/include/uapi/asm/resource.h b/arch/x86/include/uapi/asm/resource.h
> index 04bc4db8921b..0741b2a6101a 100644
> --- a/arch/x86/include/uapi/asm/resource.h
> +++ b/arch/x86/include/uapi/asm/resource.h
> @@ -1 +1,6 @@
> +/* SPDX-License-Identifier: GPL-2.0+ WITH Linux-syscall-note */
> +#ifdef CONFIG_X86_INTEL_CET
> +#define rlimit_as_extra() current->thread.cet.ibt_bitmap_size
> +#endif

Does this really belong to UAPI?

> +
>  #include <asm-generic/resource.h>
> diff --git a/include/uapi/asm-generic/resource.h b/include/uapi/asm-generic/resource.h
> index f12db7a0da64..8a7608a09700 100644
> --- a/include/uapi/asm-generic/resource.h
> +++ b/include/uapi/asm-generic/resource.h
> @@ -58,5 +58,8 @@
>  # define RLIM_INFINITY		(~0UL)
>  #endif
>  
> +#ifndef rlimit_as_extra
> +#define rlimit_as_extra() 0
> +#endif

And this?

>  #endif /* _UAPI_ASM_GENERIC_RESOURCE_H */
> diff --git a/mm/mmap.c b/mm/mmap.c
> index fa581ced3f56..397b8cb0b0af 100644
> --- a/mm/mmap.c
> +++ b/mm/mmap.c
> @@ -3237,7 +3237,17 @@ struct vm_area_struct *copy_vma(struct vm_area_struct **vmap,
>   */
>  bool may_expand_vm(struct mm_struct *mm, vm_flags_t flags, unsigned long npages)
>  {
> -	if (mm->total_vm + npages > rlimit(RLIMIT_AS) >> PAGE_SHIFT)
> +	unsigned long as_limit = rlimit(RLIMIT_AS);
> +	unsigned long as_limit_plus = as_limit + rlimit_as_extra();
> +
> +	/* as_limit_plus overflowed */
> +	if (as_limit_plus < as_limit)
> +		as_limit_plus = RLIM_INFINITY;
> +
> +	if (as_limit_plus > as_limit)
> +		as_limit = as_limit_plus;
> +
> +	if (mm->total_vm + npages > as_limit >> PAGE_SHIFT)

I wonder, how realistic a scenario where a userspace application enables IBT,
configures a huge prefetchable IO memory region (that just ignores bits
of offset beyond 16, for example), and start repeatedly loading a legacy
library there at different linear addresses.

>  		return false;
>  
>  	if (is_data_mapping(flags) &&
> -- 
> 2.17.1
>