Re: [PATCH v2 8/9] arm: KVM: Make unexpected register accesses inject an undef

[Christoffer Dall]

On Mon, Mar 27, 2017 at 05:03:44PM +0100, Marc Zyngier wrote:
> Reads from write-only system registers are generally confined to
> EL1 and not propagated to EL2 (that's what the architecture
> mantates). In order to be sure that we have a sane behaviour
> even in the unlikely event that we have a broken system, we still
> handle it in KVM. Same goes for write to RO registers.
> 
> In that case, let's inject an undef into the guest.
> 

Reviewed-by: Christoffer Dall 

> Signed-off-by: Marc Zyngier 
> ---
>  arch/arm/kvm/coproc.c | 18 ++
>  arch/arm/kvm/coproc.h | 18 --
>  2 files changed, 18 insertions(+), 18 deletions(-)
> 
> diff --git a/arch/arm/kvm/coproc.c b/arch/arm/kvm/coproc.c
> index 3e5e4194ef86..519aac12b365 100644
> --- a/arch/arm/kvm/coproc.c
> +++ b/arch/arm/kvm/coproc.c
> @@ -40,6 +40,24 @@
>   * Co-processor emulation
>   
> */
>  
> +static bool write_to_read_only(struct kvm_vcpu *vcpu,
> +const struct coproc_params *params)
> +{
> + WARN_ONCE(1, "CP15 write to read-only register\n");
> + print_cp_instr(params);
> + kvm_inject_undefined(vcpu);
> + return false;
> +}
> +
> +static bool read_from_write_only(struct kvm_vcpu *vcpu,
> +  const struct coproc_params *params)
> +{
> + WARN_ONCE(1, "CP15 read to write-only register\n");
> + print_cp_instr(params);
> + kvm_inject_undefined(vcpu);
> + return false;
> +}
> +
>  /* 3 bits per cache level, as per CLIDR, but non-existent caches always 0 */
>  static u32 cache_levels;
>  
> diff --git a/arch/arm/kvm/coproc.h b/arch/arm/kvm/coproc.h
> index eef1759c2b65..3a41b7d1eb86 100644
> --- a/arch/arm/kvm/coproc.h
> +++ b/arch/arm/kvm/coproc.h
> @@ -81,24 +81,6 @@ static inline bool read_zero(struct kvm_vcpu *vcpu,
>   return true;
>  }
>  
> -static inline bool write_to_read_only(struct kvm_vcpu *vcpu,
> -   const struct coproc_params *params)
> -{
> - kvm_debug("CP15 write to read-only register at: %08lx\n",
> -   *vcpu_pc(vcpu));
> - print_cp_instr(params);
> - return false;
> -}
> -
> -static inline bool read_from_write_only(struct kvm_vcpu *vcpu,
> - const struct coproc_params *params)
> -{
> - kvm_debug("CP15 read to write-only register at: %08lx\n",
> -   *vcpu_pc(vcpu));
> - print_cp_instr(params);
> - return false;
> -}
> -
>  /* Reset functions */
>  static inline void reset_unknown(struct kvm_vcpu *vcpu,
>const struct coproc_reg *r)
> -- 
> 2.11.0
> 
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[PATCH v2 8/9] arm: KVM: Make unexpected register accesses inject an undef

[Marc Zyngier]

Reads from write-only system registers are generally confined to
EL1 and not propagated to EL2 (that's what the architecture
mantates). In order to be sure that we have a sane behaviour
even in the unlikely event that we have a broken system, we still
handle it in KVM. Same goes for write to RO registers.

In that case, let's inject an undef into the guest.

Signed-off-by: Marc Zyngier 
---
 arch/arm/kvm/coproc.c | 18 ++
 arch/arm/kvm/coproc.h | 18 --
 2 files changed, 18 insertions(+), 18 deletions(-)

diff --git a/arch/arm/kvm/coproc.c b/arch/arm/kvm/coproc.c
index 3e5e4194ef86..519aac12b365 100644
--- a/arch/arm/kvm/coproc.c
+++ b/arch/arm/kvm/coproc.c
@@ -40,6 +40,24 @@
  * Co-processor emulation
  */
 
+static bool write_to_read_only(struct kvm_vcpu *vcpu,
+  const struct coproc_params *params)
+{
+   WARN_ONCE(1, "CP15 write to read-only register\n");
+   print_cp_instr(params);
+   kvm_inject_undefined(vcpu);
+   return false;
+}
+
+static bool read_from_write_only(struct kvm_vcpu *vcpu,
+const struct coproc_params *params)
+{
+   WARN_ONCE(1, "CP15 read to write-only register\n");
+   print_cp_instr(params);
+   kvm_inject_undefined(vcpu);
+   return false;
+}
+
 /* 3 bits per cache level, as per CLIDR, but non-existent caches always 0 */
 static u32 cache_levels;
 
diff --git a/arch/arm/kvm/coproc.h b/arch/arm/kvm/coproc.h
index eef1759c2b65..3a41b7d1eb86 100644
--- a/arch/arm/kvm/coproc.h
+++ b/arch/arm/kvm/coproc.h
@@ -81,24 +81,6 @@ static inline bool read_zero(struct kvm_vcpu *vcpu,
return true;
 }
 
-static inline bool write_to_read_only(struct kvm_vcpu *vcpu,
- const struct coproc_params *params)
-{
-   kvm_debug("CP15 write to read-only register at: %08lx\n",
- *vcpu_pc(vcpu));
-   print_cp_instr(params);
-   return false;
-}
-
-static inline bool read_from_write_only(struct kvm_vcpu *vcpu,
-   const struct coproc_params *params)
-{
-   kvm_debug("CP15 read to write-only register at: %08lx\n",
- *vcpu_pc(vcpu));
-   print_cp_instr(params);
-   return false;
-}
-
 /* Reset functions */
 static inline void reset_unknown(struct kvm_vcpu *vcpu,
 const struct coproc_reg *r)
-- 
2.11.0

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