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 _______________________________________________ Linuxppc-dev mailing list Linuxppc-dev@lists.ozlabs.org https://lists.ozlabs.org/listinfo/linuxppc-dev
