On Wed, Mar 12, 2014 at 10:32 AM, H. Peter Anvin <h...@zytor.com> wrote: > In taking about 1 here.
I'm still unconvinced that this is worth the effort. I'm okay with killing the compat vdso entirely, and I'm okay with adding a minimal, fully functional fix (like this patch set), but I don't really want to add funny interactions with ASLR to support such a narrow use case. > > On March 12, 2014 9:20:50 AM PDT, Andy Lutomirski <l...@amacapital.net> wrote: >>On Tue, Mar 11, 2014 at 11:14 PM, H. Peter Anvin <h...@zytor.com> wrote: >>> There is one sensible address: end of address space perhaps minus >>some small offset. Unlikely to be used by anything specific. >> >>Meh. The compat vdso logic will end up being either: >> >>1) Try to map at the preferred address. If it fails, don't map it. >>Force ASLR off for the vdso >> >>2) Try to map at the preferred address. If it fails, map somewhere >>else and relocate. >> >>3) Try to map at the preferred address unless ASLR is on. If it fails >>or ASLR is on, map somewhere else and relocate. >> >>since the whole point is to simplify this stuff, I don't really like >>any of these choices. That's a lot of code to save 4k per process, >>and when it breaks (which I suspect it will the next time anyone >>touches the address space layout) so one will notice that 4k gets >>wasted again. >> >>> >>> On March 11, 2014 11:09:11 PM PDT, Andy Lutomirski >><l...@amacapital.net> wrote: >>>>On Mar 11, 2014 10:02 PM, "H. Peter Anvin" <h...@zytor.com> wrote: >>>>> >>>>> On 03/11/2014 03:15 PM, Andy Lutomirski wrote: >>>>>> >>>>>> The meat of this patch series is in patch 1. Patch 2 is split out >>>>for >>>>>> improved bisectability. >>>>>> >>>>>> Changes from v1: Split into two patches and fixed a comment. >>>>>> >>>>>> Andy Lutomirski (2): >>>>>> x86: Dynamically relocate the compat vdso >>>>>> x86_32: Remove user bit from identity map PDE >>>>>> >>>>>> Documentation/kernel-parameters.txt | 18 +++- >>>>>> arch/x86/Kconfig | 24 +++-- >>>>>> arch/x86/include/asm/elf.h | 4 - >>>>>> arch/x86/include/asm/fixmap.h | 8 -- >>>>>> arch/x86/include/asm/pgtable_types.h | 7 +- >>>>>> arch/x86/include/asm/vdso.h | 5 +- >>>>>> arch/x86/vdso/vdso-layout.lds.S | 2 +- >>>>>> arch/x86/vdso/vdso32-setup.c | 173 >>>>++++++++++++++++------------------- >>>>>> arch/x86/vdso/vdso32/vdso32.lds.S | 2 - >>>>>> 9 files changed, 111 insertions(+), 132 deletions(-) >>>>>> >>>>> >>>>> Why per process? *If* we have compat vdso turned on, can't we just >>>>put it in one place system-wide? >>>> >>>>My machine has ASLR turned on, and the vma really does end up >>>>somewhere different each time. I suspect that most (?) ASLR users >>>>would happily accept the 4k hit to keep ASLR working fully. >>>> >>>>Another downside of trying to have a common address for all >>processes: >>>>someone needs to figure out what that address is. What happens if an >>>>ELF binary (or interpreter) wants to load something at the chosen >>>>address? >>>> >>>>--Andy >>> >>> -- >>> Sent from my mobile phone. Please pardon brevity and lack of >>formatting. > > -- > Sent from my mobile phone. Please pardon brevity and lack of formatting. -- Andy Lutomirski AMA Capital Management, LLC -- To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majord...@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/
