KVM: arm64: Fix 32bit PC wrap-around

commit 0225fd5e0a6a32af7af0aefac45c8ebf19dc5183 upstream.

In the unlikely event that a 32bit vcpu traps into the hypervisor
on an instruction that is located right at the end of the 32bit
range, the emulation of that instruction is going to increment
PC past the 32bit range. This isn't great, as userspace can then
observe this value and get a bit confused.

Conversly, userspace can do things like (in the context of a 64bit
guest that is capable of 32bit EL0) setting PSTATE to AArch64-EL0,
set PC to a 64bit value, change PSTATE to AArch32-USR, and observe
that PC hasn't been truncated. More confusion.

Fix both by:
- truncating PC increments for 32bit guests
- sanitizing all 32bit regs every time a core reg is changed by
  userspace, and that PSTATE indicates a 32bit mode.

Cc: stable@vger.kernel.org
Acked-by: Will Deacon <will@kernel.org>
Signed-off-by: Marc Zyngier <maz@kernel.org>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

diff --git a/arch/arm64/kvm/guest.c b/arch/arm64/kvm/guest.c
index a6c9fbaeaefcdd71d0ea70c8eeb89c55692f8b66..870e594f95edda61e785de85b92148080febd03c 100644 (file)
--- a/arch/arm64/kvm/guest.c
+++ b/arch/arm64/kvm/guest.c
@@ -179,6 +179,13 @@ static int set_core_reg(struct kvm_vcpu *vcpu, const struct kvm_one_reg *reg)
        }
 
        memcpy((u32 *)regs + off, valp, KVM_REG_SIZE(reg->id));
+
+       if (*vcpu_cpsr(vcpu) & PSR_MODE32_BIT) {
+               int i;
+
+               for (i = 0; i < 16; i++)
+                       *vcpu_reg32(vcpu, i) = (u32)*vcpu_reg32(vcpu, i);
+       }
 out:
        return err;
 }

diff --git a/virt/kvm/arm/hyp/aarch32.c b/virt/kvm/arm/hyp/aarch32.c
index d31f267961e75a956174964e445338a74abc757b..25c0e47d57cbe314ff9b993c4456c0d8fd65a0d1 100644 (file)
--- a/virt/kvm/arm/hyp/aarch32.c
+++ b/virt/kvm/arm/hyp/aarch32.c
@@ -125,12 +125,16 @@ static void __hyp_text kvm_adjust_itstate(struct kvm_vcpu *vcpu)
  */
 void __hyp_text kvm_skip_instr32(struct kvm_vcpu *vcpu, bool is_wide_instr)
 {
+       u32 pc = *vcpu_pc(vcpu);
        bool is_thumb;
 
        is_thumb = !!(*vcpu_cpsr(vcpu) & PSR_AA32_T_BIT);
        if (is_thumb && !is_wide_instr)
-               *vcpu_pc(vcpu) += 2;
+               pc += 2;
        else
-               *vcpu_pc(vcpu) += 4;
+               pc += 4;
+
+       *vcpu_pc(vcpu) = pc;
+
        kvm_adjust_itstate(vcpu);
 }