Messages in this thread | | | Subject | Re: [RFC][PATCH] Randomize kernel base address on boot | From | Dan Rosenberg <> | Date | Tue, 24 May 2011 18:55:58 -0400 |
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On Tue, 2011-05-24 at 23:02 +0200, Ingo Molnar wrote: > * Dan Rosenberg <drosenberg@vsecurity.com> wrote: > > > This introduces CONFIG_RANDOMIZE_BASE, which randomizes the address at > > which the kernel is decompressed at boot as a security feature that > > deters exploit attempts relying on knowledge of the location of kernel > > internals. The default values of the kptr_restrict and dmesg_restrict > > sysctls are set to (1) when this is enabled, since hiding kernel > > pointers is necessary to preserve the secrecy of the randomized base > > address. > > That was quick! :-) > > > This feature also uses a fixed mapping to move the IDT (if not already > > done as a fix for the F00F bug), to avoid exposing the location of > > kernel internals relative to the original IDT. This has the additional > > security benefit of marking the new virtual address of the IDT > > read-only. > > Btw., as i suggested before the IDT should be made percpu, that way we could > split out and evaluate the IDT change independently of any security > considerations, as a potential scalability improvement. Makes the decision > easier because right now moving the IDT to a 4K TLB increases the kernel's TLB > footprint a tiny bit. >
Alright, I'll start working on this.
> > Entropy is generated using the RDRAND instruction if it is supported. If not, > > then RDTSC is used, if supported. If neither RDRAND nor RDTSC are supported, > > then no randomness is introduced. Support for the CPUID instruction is > > required to check for the availability of these two instructions. > > Btw., i'd suggest to fall back not to zero but to something system specific > like RAM size or a BIOS signature such as the contents of 0xf0000 or so. This, > while clearly not random, will at least *somewhat* randomize the kernel against > remote attackers who do not know the RAM size or the system type. >
Good idea, will do.
-Dan
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