Messages in this thread | | | Date | Tue, 4 Jul 2023 14:41:36 +0100 | From | Sudeep Holla <> | Subject | Re: [PATCH v3] KVM: arm64: Use BTI for nvhe |
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On Tue, May 30, 2023 at 03:08:45PM +0000, Mostafa Saleh wrote: > CONFIG_ARM64_BTI_KERNEL compiles the kernel to support ARMv8.5-BTI. > However, the nvhe code doesn't make use of it as it doesn't map any > pages with Guarded Page(GP) bit. > > kvm pgtable code is modified to map executable pages with GP bit > if BTI is enabled for the kernel. > > At hyp init, SCTLR_EL2.BT is set to 1 to match EL1 configuration > (SCTLR_EL1.BT1) set in bti_enable(). > > One difference between kernel and nvhe code, is that the kernel maps > .text with GP while nvhe maps all the executable pages, this makes > nvhe code need to deal with special initialization code coming from > other executable sections (.idmap.text). > For this we need to add bti instruction at the beginning of > __kvm_handle_stub_hvc as it can be called by __host_hvc through > branch instruction(br) and unlike SYM_FUNC_START, SYM_CODE_START > doesn’t add bti instruction at the beginning, and it can’t be modified > to add it as it is used with vector tables. > Another solution which is more intrusive is to convert > __kvm_handle_stub_hvc to a function and inject “bti jc” instead of > “bti c” in SYM_FUNC_START >
I was chasing a bug in linux-next yesterday with protected nVHE(pKVM) and cpuidle enabled. The system fails to boot. I just bisected the issue to this patch and also saw this patch landed in the linus tree yesterday/today. Not sure if this is something to do with the fact that pKVM skips to __kvm_handle_stub_hvc in __host_hvc.
Let me know if you want be to try something.
-- Regards, Sudeep
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