Messages in this thread | | | Date | Mon, 10 Mar 2014 10:24:25 -0700 | From | "H. Peter Anvin" <> | Subject | Re: [x86, vdso] BUG: unable to handle kernel paging request at d34bd000 |
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On 03/10/2014 10:12 AM, Andy Lutomirski wrote: > On Mon, Mar 10, 2014 at 8:11 AM, Linus Torvalds > <torvalds@linux-foundation.org> wrote: >> >> On Mar 10, 2014 8:01 AM, "H. Peter Anvin" <hpa@linux.intel.com> wrote: >>> >>> I have mentioned in the past wanting to move the fixmap to the low part >>> of the kernel space, because the top isn't really fixed... >> >> How about the high part of the user address space, just above the stack? >> Leave a unmapped page in between, or something. The stack is already >> randomized, isn't it? > > For the !compat_vdso case, I don't like it -- this will put the vdso > (which is executable) at a constant offset from the stack, which will > make it much easier to use the vdso to defeat ASLR. > > For the compat_vdso case, this only works if the address is *not* > random, unless we're going to start giving each process its very own > relocated vdso. >
I presumed we were talking about compat_vdso, which thus simply turns into a "don't randomize the vdso flag." A significant side benefit is that this should make the code more similar.
> For 64-bit, this is an entirely different story. The vsyscall page is > stuck in the fixmap forever, although I want to add a way for > userspace to opt out. The vvar page, hpet, etc could move into vmas, > though. I kind of want to do that anyway to allow processes to turn > off the ability to read the clock.
Wait... you want to do what?!
-hpa
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