linux-kernel - Re: [PATCH 2/2] x86/mmap: handle worst-case heap randomization in mmap

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Date:   Tue, 26 Mar 2019 09:43:36 +0100 (CET)
From:   Thomas Gleixner <tglx@...utronix.de>
To:     "Saidi, Ali" <alisaidi@...zon.com>
cc:     Dave Hansen <dave.hansen@...ux.intel.com>,
        Kees Cook <keescook@...omium.org>,
        Peter Zijlstra <peterz@...radead.org>,
        Catalin Marinas <catalin.marinas@....com>,
        "x86@...nel.org" <x86@...nel.org>,
        Will Deacon <will.deacon@....com>,
        "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
        Ingo Molnar <mingo@...hat.com>, Borislav Petkov <bp@...en8.de>,
        "Woodhouse, David" <dwmw@...zon.co.uk>,
        Andy Lutomirski <luto@...nel.org>,
        "H. Peter Anvin" <hpa@...or.com>,
        Andrew Morton <akpm@...ux-foundation.org>,
        "linux-arm-kernel@...ts.infradead.org" 
        <linux-arm-kernel@...ts.infradead.org>,
        "Liguori, Anthony" <aliguori@...zon.com>
Subject: Re: [PATCH 2/2] x86/mmap: handle worst-case heap randomization in
 mmap_base

On Tue, 26 Mar 2019, Saidi, Ali wrote:
> On 3/21/19, 9:11 AM, "linux-arm-kernel on behalf of Thomas Gleixner" <linux-arm-kernel-bounces@...ts.infradead.org on behalf of tglx@...utronix.de> wrote:
> 
>     On Tue, 12 Mar 2019, Ali Saidi wrote:
>     
>     > Increase mmap_base by the worst-case brk randomization so that
>     > the stack and heap remain apart.
>     > 
>     > In Linux 4.13 a change was committed that special cased the kernel ELF
>     > loader when the loader is invoked directly (eab09532d400; binfmt_elf: use
>     > ELF_ET_DYN_BASE only for PIE). Generally, the loader isn’t invoked
>     > directly and this issue is limited to cases where it is, (e.g to set a
>     > non-inheritable LD_LIBRARY_PATH, testing new versions of the loader). In
>     > those rare cases, the loader doesn't take into account the amount of brk
>     > randomization that will be applied by arch_randomize_brk(). This can
>     > lead to the stack and heap being arbitrarily close to each other.
>     
>     That explains not why you need this change. What's the consequence of them
>     being close to each other?
>
> The process doesn't get it's requested stack size and stack allocations
> could end up scribbling on the heap.

And exactly that information wants to be in the changelog.

Thanks,

	tglx