Re: [PATCH v7 09/11] arm64: disable SCS for hypervisor code
From: James Morse <james.morse@arm.com>
Date: 2020-02-10 17:19:05
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Hi Sami, On 28/01/2020 18:49, Sami Tolvanen wrote:
Filter out CC_FLAGS_SCS and -ffixed-x18 for code that runs at a different exception level.
Hmmm, there are two things being disabled here.
Stashing the lr in memory pointed to by VA won't work transparently at EL2 ... but
shouldn't KVM's C code still treat x18 as a fixed register?
As you have an __attribute__((no_sanitize("shadow-call-stack"))), could we add that to
__hyp_text instead? (its a smaller hammer!) All of KVM's EL2 code is marked __hyp_text,
but that isn't everything in these files. Doing it like this would leave KVM's VHE-only
paths covered.
As an example, with VHE the kernel and KVM both run at EL2, and KVM behaves differently:
kvm_vcpu_put_sysregs() in kvm/hyp/sysreg-sr.c is called from a preempt notifier as
the EL2 registers are always accessible.
Thanks,
James
quoted hunk ↗ jump to hunk
diff --git a/arch/arm64/kvm/hyp/Makefile b/arch/arm64/kvm/hyp/Makefile index ea710f674cb6..5843adef9ef6 100644 --- a/arch/arm64/kvm/hyp/Makefile +++ b/arch/arm64/kvm/hyp/Makefile@@ -28,3 +28,6 @@ GCOV_PROFILE := n KASAN_SANITIZE := n UBSAN_SANITIZE := n KCOV_INSTRUMENT := n + +# remove the SCS flags from all objects in this directory +KBUILD_CFLAGS := $(filter-out -ffixed-x18 $(CC_FLAGS_SCS), $(KBUILD_CFLAGS))
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