In taking about 1 here. 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.
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