Hi James,
On Fri, Jan 4, 2019 at 11:32 PM James Morse [off-list ref] wrote:

Hi Amit,

On 18/12/2018 07:56, Amit Daniel Kachhap wrote:

quoted

According to userspace settings, pointer authentication cpufeature
is enabled/disabled from guests.

This reads like the guest is changing something in the host. Isn't this hiding
the id-register values from the guest?

I dropped this patch altogether in V5 series and now only key
registers are masked
if userspace disables it.

Thanks,
Amit Daniel

quoted

diff --git a/arch/arm64/kvm/sys_regs.c b/arch/arm64/kvm/sys_regs.c
index 6af6c7d..ce6144a 100644
--- a/arch/arm64/kvm/sys_regs.c
+++ b/arch/arm64/kvm/sys_regs.c

@@ -1066,6 +1066,15 @@ static u64 read_id_reg(struct sys_reg_desc const *r, bool raz)
                      kvm_debug("SVE unsupported for guests, suppressing\n");

              val &= ~(0xfUL << ID_AA64PFR0_SVE_SHIFT);
+     } else if (id == SYS_ID_AA64ISAR1_EL1) {
+             const u64 ptrauth_mask = (0xfUL << ID_AA64ISAR1_APA_SHIFT) |
+                                      (0xfUL << ID_AA64ISAR1_API_SHIFT) |
+                                      (0xfUL << ID_AA64ISAR1_GPA_SHIFT) |
+                                      (0xfUL << ID_AA64ISAR1_GPI_SHIFT);
+             if (!kvm_arm_vcpu_ptrauth_allowed(vcpu)) {
+                     kvm_debug("ptrauth unsupported for guests, suppressing\n");
+                     val &= ~ptrauth_mask;
+             }

I think this hunk should have been in the previous patch as otherwise its a
bisection oddity.

Could you merge this hunk with the previous patch, and move the mechanical bits
that pass vcpu around to a prior preparatory patch.

(I'm still unsure if we need to hide this as a user-controlled policy)


Thanks,

James

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