[Xen-devel,v2,04/15] xen/arm: vsmc: Implement SMCCC_ARCH_WORKAROUND_1 BP hardening support

Message ID 20180208192203.9556-5-julien.grall@arm.com
State Superseded
Headers show
Series
  • xen/arm: PSCI 1.1 and SMCCC-1.1 support and XSA-254 variant 2 update
Related show

Commit Message

Julien Grall Feb. 8, 2018, 7:21 p.m.
SMCCC 1.1 offers firmware-based CPU workarounds. In particular,
SMCCC_ARCH_WORKAROUND_1 provides BP hardening for variant 2 of XSA-254
(CVE-2017-5715).

If the hypervisor has some mitigation for this issue, report that we
deal with it using SMCCC_ARCH_WORKAROUND_1, as we apply the hypervisor
workaround on every guest exit.

Signed-off-by: Julien Grall <julien.grall@arm.com>
Reviewed-by: Volodymyr Babchuk <volodymyr.babchuk@epam.com>

---
    Changes in v2:
        - Add Volodymyr's reviewed-by
---
 xen/arch/arm/vsmc.c         | 22 ++++++++++++++++++++--
 xen/include/asm-arm/smccc.h |  6 ++++++
 2 files changed, 26 insertions(+), 2 deletions(-)

Comments

Stefano Stabellini Feb. 20, 2018, 12:26 a.m. | #1
On Thu, 8 Feb 2018, Julien Grall wrote:
> SMCCC 1.1 offers firmware-based CPU workarounds. In particular,
> SMCCC_ARCH_WORKAROUND_1 provides BP hardening for variant 2 of XSA-254
> (CVE-2017-5715).
> 
> If the hypervisor has some mitigation for this issue, report that we
> deal with it using SMCCC_ARCH_WORKAROUND_1, as we apply the hypervisor
> workaround on every guest exit.
> 
> Signed-off-by: Julien Grall <julien.grall@arm.com>
> Reviewed-by: Volodymyr Babchuk <volodymyr.babchuk@epam.com>

Acked-by: Stefano Stabellini <sstabellini@kernel.org>


> ---
>     Changes in v2:
>         - Add Volodymyr's reviewed-by
> ---
>  xen/arch/arm/vsmc.c         | 22 ++++++++++++++++++++--
>  xen/include/asm-arm/smccc.h |  6 ++++++
>  2 files changed, 26 insertions(+), 2 deletions(-)
> 
> diff --git a/xen/arch/arm/vsmc.c b/xen/arch/arm/vsmc.c
> index a708aa5e81..144a1cd761 100644
> --- a/xen/arch/arm/vsmc.c
> +++ b/xen/arch/arm/vsmc.c
> @@ -18,6 +18,7 @@
>  #include <xen/lib.h>
>  #include <xen/types.h>
>  #include <public/arch-arm/smccc.h>
> +#include <asm/cpufeature.h>
>  #include <asm/monitor.h>
>  #include <asm/regs.h>
>  #include <asm/smccc.h>
> @@ -93,8 +94,25 @@ static bool handle_arch(struct cpu_user_regs *regs)
>          return true;
>  
>      case ARM_SMCCC_ARCH_FEATURES_FID:
> -        /* Nothing supported yet */
> -        set_user_reg(regs, 0, -1);
> +    {
> +        uint32_t arch_func_id = get_user_reg(regs, 1);
> +        int ret = -1;
> +
> +        switch ( arch_func_id )
> +        {
> +        case ARM_SMCCC_ARCH_WORKAROUND_1_FID:
> +            if ( cpus_have_cap(ARM_HARDEN_BRANCH_PREDICTOR) )
> +                ret = 0;
> +            break;
> +        }
> +
> +        set_user_reg(regs, 0, ret);
> +
> +        return true;
> +    }
> +
> +    case ARM_SMCCC_ARCH_WORKAROUND_1_FID:
> +        /* No return value */
>          return true;
>      }
>  
> diff --git a/xen/include/asm-arm/smccc.h b/xen/include/asm-arm/smccc.h
> index 431389c118..b790fac17c 100644
> --- a/xen/include/asm-arm/smccc.h
> +++ b/xen/include/asm-arm/smccc.h
> @@ -115,6 +115,12 @@ static inline uint32_t smccc_get_owner(register_t funcid)
>                         ARM_SMCCC_OWNER_ARCH,        \
>                         0x1)
>  
> +#define ARM_SMCCC_ARCH_WORKAROUND_1_FID             \
> +    ARM_SMCCC_CALL_VAL(ARM_SMCCC_FAST_CALL,         \
> +                      ARM_SMCCC_CONV_32,            \
> +                      ARM_SMCCC_OWNER_ARCH,         \
> +                      0x8000)
> +
>  /* Only one error code defined in SMCCC */
>  #define ARM_SMCCC_ERR_UNKNOWN_FUNCTION  (-1)
>  
> -- 
> 2.11.0
>

Patch

diff --git a/xen/arch/arm/vsmc.c b/xen/arch/arm/vsmc.c
index a708aa5e81..144a1cd761 100644
--- a/xen/arch/arm/vsmc.c
+++ b/xen/arch/arm/vsmc.c
@@ -18,6 +18,7 @@ 
 #include <xen/lib.h>
 #include <xen/types.h>
 #include <public/arch-arm/smccc.h>
+#include <asm/cpufeature.h>
 #include <asm/monitor.h>
 #include <asm/regs.h>
 #include <asm/smccc.h>
@@ -93,8 +94,25 @@  static bool handle_arch(struct cpu_user_regs *regs)
         return true;
 
     case ARM_SMCCC_ARCH_FEATURES_FID:
-        /* Nothing supported yet */
-        set_user_reg(regs, 0, -1);
+    {
+        uint32_t arch_func_id = get_user_reg(regs, 1);
+        int ret = -1;
+
+        switch ( arch_func_id )
+        {
+        case ARM_SMCCC_ARCH_WORKAROUND_1_FID:
+            if ( cpus_have_cap(ARM_HARDEN_BRANCH_PREDICTOR) )
+                ret = 0;
+            break;
+        }
+
+        set_user_reg(regs, 0, ret);
+
+        return true;
+    }
+
+    case ARM_SMCCC_ARCH_WORKAROUND_1_FID:
+        /* No return value */
         return true;
     }
 
diff --git a/xen/include/asm-arm/smccc.h b/xen/include/asm-arm/smccc.h
index 431389c118..b790fac17c 100644
--- a/xen/include/asm-arm/smccc.h
+++ b/xen/include/asm-arm/smccc.h
@@ -115,6 +115,12 @@  static inline uint32_t smccc_get_owner(register_t funcid)
                        ARM_SMCCC_OWNER_ARCH,        \
                        0x1)
 
+#define ARM_SMCCC_ARCH_WORKAROUND_1_FID             \
+    ARM_SMCCC_CALL_VAL(ARM_SMCCC_FAST_CALL,         \
+                      ARM_SMCCC_CONV_32,            \
+                      ARM_SMCCC_OWNER_ARCH,         \
+                      0x8000)
+
 /* Only one error code defined in SMCCC */
 #define ARM_SMCCC_ERR_UNKNOWN_FUNCTION  (-1)