From: Alan Modra <amodra@gmail•com>
To: Florian Weimer <fweimer@redhat•com>
Cc: linuxppc-dev@lists•ozlabs.org
Subject: Re: ppc64 sbrk returns executable heap in 32-bit emulation mode
Date: Mon, 16 May 2016 15:54:25 +0930 [thread overview]
Message-ID: <20160516062425.GA24091@bubble.grove.modra.org> (raw)
In-Reply-To: <5590cf46-aaa2-451e-f21d-acf5f2eb4928@redhat.com>
On Thu, May 12, 2016 at 03:41:09PM +0200, Florian Weimer wrote:
> We noticed that on ppc64, the sbrk system call in the 32-bit subsystem
> returns executable memory. I assume it is related to this, in
> arch/powerpc/include/asm/page.h:
>
> /*
> * Unfortunately the PLT is in the BSS in the PPC32 ELF ABI,
> * and needs to be executable. This means the whole heap ends
> * up being executable.
> */
> #define VM_DATA_DEFAULT_FLAGS32 (VM_READ | VM_WRITE | VM_EXEC | \
> VM_MAYREAD | VM_MAYWRITE | VM_MAYEXEC)
>
>
> What is the rationale for this? This comment must be *really* old,
I think the comment is just plain wrong. ppc32 needs an executable
stack because it builds trampolines on the stack to support calling
nested functions. I presume that's why the heap is executable. (If
I'm wrong about heap+stack needing the same protection then I can't
think of any reason to require an executable heap.)
> because ld.so in glibc should make sure that the PLT is executable. And
> for current binaries, .bss is *not* executable, contrary to what the
> comment suggests.
>
> Is this comment about pre-ELF binaries? If yes, would it possible to
> change the default for ELF binaries?
>
> Thanks,
> Florian
--
Alan Modra
Australia Development Lab, IBM
next prev parent reply other threads:[~2016-05-16 6:24 UTC|newest]
Thread overview: 7+ messages / expand[flat|nested] mbox.gz Atom feed top
2016-05-12 13:41 ppc64 sbrk returns executable heap in 32-bit emulation mode Florian Weimer
2016-05-16 6:24 ` Alan Modra [this message]
2016-05-16 8:51 ` Florian Weimer
[not found] ` <20160516062425.GA24091__32035.8907142237$1463379977$gmane$org@bubble.grove.modra.org>
2016-05-16 8:49 ` Andreas Schwab
2016-05-16 8:59 ` Florian Weimer
2016-05-16 9:09 ` Andreas Schwab
2016-05-16 16:27 ` Florian Weimer
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