Re: [Xen-devel] [PATCH v3 03/17] xen/arm: vsmc: Implement SMCCC_ARCH_WORKAROUND_1 BP hardening support

[Andre Przywara <andre.przywara@xxxxxxxxxx>]

Hi,

On 15/02/18 15:02, 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@xxxxxxx>
> Reviewed-by: Volodymyr Babchuk <volodymyr.babchuk@xxxxxxxx>
> 
> ---
>     Changes in v3:
>         - Fix minor conflict during rebase
> 
>     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 7ec492741b..40a80d5760 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, ARM_SMCCC_NOT_SUPPORTED);
> +    {
> +        uint32_t arch_func_id = get_user_reg(regs, 1);

Shouldn't the function identifier be in x0/r0?

Cheers,
Andre.

> +        int ret = ARM_SMCCC_NOT_SUPPORTED;
> +
> +        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 629cc5150b..2951caa49d 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)
> +
>  /* SMCCC error codes */
>  #define ARM_SMCCC_ERR_UNKNOWN_FUNCTION  (-1)
>  #define ARM_SMCCC_NOT_SUPPORTED         (-1)
> 

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