Re: [Xen-devel] [PATCH 5/7] xen/arm: vsmc: Implement SMCCC_ARCH_WORKAROUND_1 BP hardening support

[Volodymyr Babchuk <vlad.babchuk@xxxxxxxxx>]

Hi,

On 5 February 2018 at 15:20, Julien Grall <julien.grall@xxxxxxx> 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.
Just to be sure: is there some way to disable this workaround?


>
> Signed-off-by: Julien Grall <julien.grall@xxxxxxx>
> ---
>  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;
I think that register_t will suit better in this case.

> +
> +        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
>
>
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-- 
WBR Volodymyr Babchuk aka lorc [+380976646013]
mailto: vlad.babchuk@xxxxxxxxx

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