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

[Thomas Gleixner]

On Tue, 26 Mar 2019, Saidi, Ali wrote:
> ïOn 3/21/19, 9:11 AM, "linux-arm-kernel on behalf of Thomas Gleixner" <linux-arm-kernel-bounces@xxxxxxxxxxxxxxxxxxx on behalf of tglx@xxxxxxxxxxxxx> 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 isnât 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