On 15/03/18 15:57, Andrew Jones wrote: > On Wed, Mar 14, 2018 at 04:50:23PM +0000, Marc Zyngier wrote: >> Whilst KVM benefits from the kernel randomisation via KASLR, there is >> no additional randomisation when the kernel is running at EL1, as we >> directly use a fixed offset from the linear mapping. This is not >> necessarily a problem, but we could do a bit better by independently >> randomizing the HYP placement. >> >> This series proposes to randomise the offset by inserting a few random >> bits between the MSB of the RAM linear mapping and the top of the HYP >> VA (VA_BITS - 2). That's not a lot of random bits (on my Mustang, I >> get 13 bits), but that's better than nothing. >> >> In order to achieve this, we need to be able to patch dynamic values >> in the kernel text. This results in a bunch of changes to the >> alternative framework, the insn library, and a few more hacks in KVM >> itself (we get a new way to map the GIC at EL2). >> >> Another (and more recent) goal of this series is to work around what >> has been described as "variant 3a", which covers speculative reads of >> privileged system registers. Randomizing the location of the >> hypervisor would be pointless if one could simply obtain VBAR_EL2. In >> order to work around this, we place the vectors at a fairly static >> location (next to the idmap), independently of the hypervisor's own >> mappings. This ensures that we can leak VBAR_EL2 without disclosing >> much about HYP itself (and is similar to what the rest of the kernel >> does with KPTI). This is only enabled at runtime for Cortex-A57 and >> Cortex-A72. >> >> This has been tested on the FVP model, Seattle (both 39 and 48bit VA), >> Mustang and Thunder-X. I've also done a sanity check on 32bit (which >> is only impacted by the HYP IO VA stuff). >> > > I've smoke tested this series on a seattle with several busy VMs running > simultaneously. My host kernel configures 64K pages. I didn't see any > problems. Excellent, thanks for testing. Out of curiosity: do you have a firmware that implements the SMCCC_ARCH_WORKAROUND_1 call or not? M. -- Jazz is not dead. It just smells funny...
