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

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Message-ID: <3A8AEAFE-315E-48D2-A246-D7BF1EBB9FF8@amazon.com>
Date:   Sun, 17 Mar 2019 15:52:08 +0000
From:   "Saidi, Ali" <alisaidi@...zon.com>
To:     Dave Hansen <dave.hansen@...el.com>
CC:     "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
        "linux-arm-kernel@...ts.infradead.org" 
        <linux-arm-kernel@...ts.infradead.org>,
        "x86@...nel.org" <x86@...nel.org>,
        "H. Peter Anvin" <hpa@...or.com>,
        Andrew Morton <akpm@...ux-foundation.org>,
        Kees Cook <keescook@...omium.org>,
        Borislav Petkov <bp@...en8.de>,
        "Ingo Molnar" <mingo@...hat.com>,
        Thomas Gleixner <tglx@...utronix.de>,
        "Peter Zijlstra" <peterz@...radead.org>,
        Andy Lutomirski <luto@...nel.org>,
        "Dave Hansen" <dave.hansen@...ux.intel.com>,
        Will Deacon <will.deacon@....com>,
        Catalin Marinas <catalin.marinas@....com>,
        "Woodhouse, David" <dwmw@...zon.co.uk>,
        "Liguori, Anthony" <aliguori@...zon.com>
Subject: Re: [PATCH 2/2] x86/mmap: handle worst-case heap randomization in
 mmap_base



> On Mar 13, 2019, at 11:26 AM, Dave Hansen <dave.hansen@...el.com> wrote:
> 
>> On 3/12/19 10:32 AM, Ali Saidi wrote:
>> +    /* Provide space for brk randomization */
>> +    pad += SZ_32M;
> 
> Just curious:  Why is the padding in your other patch conditional on the
> 32-bit vs. 64-bit apps, but here it's always 32M?
Arm changes the amount of brk based on the process being 32 vs 64 bit. X86 doesn’t appear to do this. 
> 
> Also, did you hit this problem in practice somehow?

Just debugging a crash when testing a version of a library I compiled. 

Ali