Re: [PATCH V16 2/8] KVM: arm64: Prevent guest accesses into BRBE system registers/instructions

[Suzuki K Poulose <suzuki.poulose@arm.com>]

On 25/01/2024 09:41, Anshuman Khandual wrote:
> Currently BRBE feature is not supported in a guest environment. This hides
> BRBE feature availability via masking ID_AA64DFR0_EL1.BRBE field. This also
> blocks guest accesses into BRBE system registers and instructions as if the
> underlying hardware never implemented FEAT_BRBE feature.
> 
> Cc: Marc Zyngier <maz@kernel.org>
> Cc: Oliver Upton <oliver.upton@linux.dev>
> Cc: James Morse <james.morse@arm.com>
> Cc: Suzuki K Poulose <suzuki.poulose@arm.com>
> Cc: Catalin Marinas <catalin.marinas@arm.com>
> Cc: Will Deacon <will@kernel.org>
> Cc: kvmarm@lists.linux.dev
> Cc: linux-arm-kernel@lists.infradead.org
> Cc: linux-kernel@vger.kernel.org
> Signed-off-by: Anshuman Khandual <anshuman.khandual@arm.com>
> ---
> Changes in V16:
> 
> - Added BRB_INF_SRC_TGT_EL1 macro for corresponding BRB_[INF|SRC|TGT] expansion
> 
>   arch/arm64/kvm/sys_regs.c | 56 +++++++++++++++++++++++++++++++++++++++
>   1 file changed, 56 insertions(+)
> 
> diff --git a/arch/arm64/kvm/sys_regs.c b/arch/arm64/kvm/sys_regs.c
> index 30253bd19917..6a06dc2f0c06 100644
> --- a/arch/arm64/kvm/sys_regs.c
> +++ b/arch/arm64/kvm/sys_regs.c
> @@ -1304,6 +1304,11 @@ static int set_pmcr(struct kvm_vcpu *vcpu, const struct sys_reg_desc *r,
>   	return 0;
>   }
>   
> +#define BRB_INF_SRC_TGT_EL1(n)					\
> +	{ SYS_DESC(SYS_BRBINF##n##_EL1), undef_access },	\
> +	{ SYS_DESC(SYS_BRBSRC##n##_EL1), undef_access },	\
> +	{ SYS_DESC(SYS_BRBTGT##n##_EL1), undef_access }		\
> +
>   /* Silly macro to expand the DBG{BCR,BVR,WVR,WCR}n_EL1 registers in one go */
>   #define DBG_BCR_BVR_WCR_WVR_EL1(n)					\
>   	{ SYS_DESC(SYS_DBGBVRn_EL1(n)),					\
> @@ -1707,6 +1712,9 @@ static u64 read_sanitised_id_aa64dfr0_el1(struct kvm_vcpu *vcpu,
>   	/* Hide SPE from guests */
>   	val &= ~ID_AA64DFR0_EL1_PMSVer_MASK;
>   
> +	/* Hide BRBE from guests */
> +	val &= ~ID_AA64DFR0_EL1_BRBE_MASK;
> +
>   	return val;
>   }
>   
> @@ -2195,6 +2203,8 @@ static const struct sys_reg_desc sys_reg_descs[] = {
>   	{ SYS_DESC(SYS_DC_CISW), access_dcsw },
>   	{ SYS_DESC(SYS_DC_CIGSW), access_dcgsw },
>   	{ SYS_DESC(SYS_DC_CIGDSW), access_dcgsw },
> +	{ SYS_DESC(OP_BRB_IALL), undef_access },
> +	{ SYS_DESC(OP_BRB_INJ), undef_access },
>   

heads up: This may conflict with Marc's patches to move the sys 
instructions to a separate table. But otherwise, looks good to me.


Suzuki