This is a note to let you know that I've just added the patch titled KVM: arm64: Fix S1PTW handling on RO memslots to the 5.4-stable tree which can be found at: http://www.kernel.org/git/?p=linux/kernel/git/stable/stable-queue.git;a=summary The filename of the patch is: kvm-arm64-fix-s1ptw-handling-on-ro-memslots.patch and it can be found in the queue-5.4 subdirectory. If you, or anyone else, feels it should not be added to the stable tree, please let <stable@xxxxxxxxxxxxxxx> know about it. >From 406504c7b0405d74d74c15a667cd4c4620c3e7a9 Mon Sep 17 00:00:00 2001 From: Marc Zyngier <maz@xxxxxxxxxx> Date: Tue, 20 Dec 2022 14:03:52 +0000 Subject: KVM: arm64: Fix S1PTW handling on RO memslots From: Marc Zyngier <maz@xxxxxxxxxx> commit 406504c7b0405d74d74c15a667cd4c4620c3e7a9 upstream. A recent development on the EFI front has resulted in guests having their page tables baked in the firmware binary, and mapped into the IPA space as part of a read-only memslot. Not only is this legitimate, but it also results in added security, so thumbs up. It is possible to take an S1PTW translation fault if the S1 PTs are unmapped at stage-2. However, KVM unconditionally treats S1PTW as a write to correctly handle hardware AF/DB updates to the S1 PTs. Furthermore, KVM injects an exception into the guest for S1PTW writes. In the aforementioned case this results in the guest taking an abort it won't recover from, as the S1 PTs mapping the vectors suffer from the same problem. So clearly our handling is... wrong. Instead, switch to a two-pronged approach: - On S1PTW translation fault, handle the fault as a read - On S1PTW permission fault, handle the fault as a write This is of no consequence to SW that *writes* to its PTs (the write will trigger a non-S1PTW fault), and SW that uses RO PTs will not use HW-assisted AF/DB anyway, as that'd be wrong. Only in the case described in c4ad98e4b72c ("KVM: arm64: Assume write fault on S1PTW permission fault on instruction fetch") do we end-up with two back-to-back faults (page being evicted and faulted back). I don't think this is a case worth optimising for. Fixes: c4ad98e4b72c ("KVM: arm64: Assume write fault on S1PTW permission fault on instruction fetch") Reviewed-by: Oliver Upton <oliver.upton@xxxxxxxxx> Reviewed-by: Ard Biesheuvel <ardb@xxxxxxxxxx> Regression-tested-by: Ard Biesheuvel <ardb@xxxxxxxxxx> Signed-off-by: Marc Zyngier <maz@xxxxxxxxxx> Cc: stable@xxxxxxxxxxxxxxx Signed-off-by: Greg Kroah-Hartman <gregkh@xxxxxxxxxxxxxxxxxxx> --- arch/arm64/include/asm/kvm_emulate.h | 22 ++++++++++++++++++++-- 1 file changed, 20 insertions(+), 2 deletions(-) --- a/arch/arm64/include/asm/kvm_emulate.h +++ b/arch/arm64/include/asm/kvm_emulate.h @@ -378,8 +378,26 @@ static inline int kvm_vcpu_sys_get_rt(st static inline bool kvm_is_write_fault(struct kvm_vcpu *vcpu) { - if (kvm_vcpu_abt_iss1tw(vcpu)) - return true; + if (kvm_vcpu_abt_iss1tw(vcpu)) { + /* + * Only a permission fault on a S1PTW should be + * considered as a write. Otherwise, page tables baked + * in a read-only memslot will result in an exception + * being delivered in the guest. + * + * The drawback is that we end-up faulting twice if the + * guest is using any of HW AF/DB: a translation fault + * to map the page containing the PT (read only at + * first), then a permission fault to allow the flags + * to be set. + */ + switch (kvm_vcpu_trap_get_fault_type(vcpu)) { + case ESR_ELx_FSC_PERM: + return true; + default: + return false; + } + } if (kvm_vcpu_trap_is_iabt(vcpu)) return false; Patches currently in stable-queue which might be from maz@xxxxxxxxxx are queue-5.4/irqchip-gic-pm-use-pm_runtime_resume_and_get-in-gic_.patch queue-5.4/kvm-arm64-fix-s1ptw-handling-on-ro-memslots.patch