[PATCH V16 2/8] KVM: arm64: Prevent guest accesses into BRBE system registers/instructions
Anshuman Khandual
anshuman.khandual at arm.com
Thu Feb 22 23:28:48 PST 2024
On 2/21/24 19:31, Mark Rutland wrote:
> On Thu, Jan 25, 2024 at 03:11:13PM +0530, 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.
>
> Does that means that a guest can currently see BRBE advertised in the
> ID_AA64DFR0_EL1.BRB field, or is that hidden by the regular cpufeature code
> today?
IIRC it is hidden, but will have to double check. When experimenting for BRBE
guest support enablement earlier, following changes were need for the feature
to be visible in ID_AA64DFR0_EL1.
diff --git a/arch/arm64/kernel/cpufeature.c b/arch/arm64/kernel/cpufeature.c
index 646591c67e7a..f258568535a8 100644
--- a/arch/arm64/kernel/cpufeature.c
+++ b/arch/arm64/kernel/cpufeature.c
@@ -445,6 +445,7 @@ static const struct arm64_ftr_bits ftr_id_mmfr0[] = {
};
static const struct arm64_ftr_bits ftr_id_aa64dfr0[] = {
+ S_ARM64_FTR_BITS(FTR_VISIBLE, FTR_STRICT, FTR_LOWER_SAFE, ID_AA64DFR0_EL1_BRBE_SHIFT, 4, ID_AA64DFR0_EL1_BRBE_IMP),
S_ARM64_FTR_BITS(FTR_HIDDEN, FTR_STRICT, FTR_LOWER_SAFE, ID_AA64DFR0_EL1_DoubleLock_SHIFT, 4, 0),
ARM64_FTR_BITS(FTR_HIDDEN, FTR_NONSTRICT, FTR_LOWER_SAFE, ID_AA64DFR0_EL1_PMSVer_SHIFT, 4, 0),
ARM64_FTR_BITS(FTR_HIDDEN, FTR_STRICT, FTR_LOWER_SAFE, ID_AA64DFR0_EL1_CTX_CMPs_SHIFT, 4, 0),
Should we add the following entry - explicitly hiding BRBE from the guest
as a prerequisite patch ?
S_ARM64_FTR_BITS(FTR_HIDDEN, FTR_STRICT, FTR_LOWER_SAFE, ID_AA64DFR0_EL1_BRBE_SHIFT, 4, ID_AA64DFR0_EL1_BRBE_NI)
>
>> 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 at kernel.org>
>> Cc: Oliver Upton <oliver.upton at linux.dev>
>> Cc: James Morse <james.morse at arm.com>
>> Cc: Suzuki K Poulose <suzuki.poulose at arm.com>
>> Cc: Catalin Marinas <catalin.marinas at arm.com>
>> Cc: Will Deacon <will at kernel.org>
>> Cc: kvmarm at lists.linux.dev
>> Cc: linux-arm-kernel at lists.infradead.org
>> Cc: linux-kernel at vger.kernel.org
>> Signed-off-by: Anshuman Khandual <anshuman.khandual at 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 } \
>
> With the changes suggested on the previous patch, this would need to change to be:
>
> #define BRB_INF_SRC_TGT_EL1(n) \
> { SYS_DESC(SYS_BRBINF_EL1(n)), undef_access }, \
> { SYS_DESC(SYS_BRBSRC_EL1(n)), undef_access }, \
> { SYS_DESC(SYS_BRBTGT_EL1(n)), undef_access } \
Sure, already folded back in these above changes.
>
>
> ... which would also be easier for backporting (if necessary), since those
> definitions have existed for a while.
>
> Otherwise (modulo Suzuki's comment about rebasing), this looks good to me.
Okay.
>
> Mark.
>
>> /* 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 },
>>
>> DBG_BCR_BVR_WCR_WVR_EL1(0),
>> DBG_BCR_BVR_WCR_WVR_EL1(1),
>> @@ -2225,6 +2235,52 @@ static const struct sys_reg_desc sys_reg_descs[] = {
>> { SYS_DESC(SYS_DBGCLAIMCLR_EL1), trap_raz_wi },
>> { SYS_DESC(SYS_DBGAUTHSTATUS_EL1), trap_dbgauthstatus_el1 },
>>
>> + /*
>> + * BRBE branch record sysreg address space is interleaved between
>> + * corresponding BRBINF<N>_EL1, BRBSRC<N>_EL1, and BRBTGT<N>_EL1.
>> + */
>> + BRB_INF_SRC_TGT_EL1(0),
>> + BRB_INF_SRC_TGT_EL1(16),
>> + BRB_INF_SRC_TGT_EL1(1),
>> + BRB_INF_SRC_TGT_EL1(17),
>> + BRB_INF_SRC_TGT_EL1(2),
>> + BRB_INF_SRC_TGT_EL1(18),
>> + BRB_INF_SRC_TGT_EL1(3),
>> + BRB_INF_SRC_TGT_EL1(19),
>> + BRB_INF_SRC_TGT_EL1(4),
>> + BRB_INF_SRC_TGT_EL1(20),
>> + BRB_INF_SRC_TGT_EL1(5),
>> + BRB_INF_SRC_TGT_EL1(21),
>> + BRB_INF_SRC_TGT_EL1(6),
>> + BRB_INF_SRC_TGT_EL1(22),
>> + BRB_INF_SRC_TGT_EL1(7),
>> + BRB_INF_SRC_TGT_EL1(23),
>> + BRB_INF_SRC_TGT_EL1(8),
>> + BRB_INF_SRC_TGT_EL1(24),
>> + BRB_INF_SRC_TGT_EL1(9),
>> + BRB_INF_SRC_TGT_EL1(25),
>> + BRB_INF_SRC_TGT_EL1(10),
>> + BRB_INF_SRC_TGT_EL1(26),
>> + BRB_INF_SRC_TGT_EL1(11),
>> + BRB_INF_SRC_TGT_EL1(27),
>> + BRB_INF_SRC_TGT_EL1(12),
>> + BRB_INF_SRC_TGT_EL1(28),
>> + BRB_INF_SRC_TGT_EL1(13),
>> + BRB_INF_SRC_TGT_EL1(29),
>> + BRB_INF_SRC_TGT_EL1(14),
>> + BRB_INF_SRC_TGT_EL1(30),
>> + BRB_INF_SRC_TGT_EL1(15),
>> + BRB_INF_SRC_TGT_EL1(31),
>> +
>> + /* Remaining BRBE sysreg addresses space */
>> + { SYS_DESC(SYS_BRBCR_EL1), undef_access },
>> + { SYS_DESC(SYS_BRBFCR_EL1), undef_access },
>> + { SYS_DESC(SYS_BRBTS_EL1), undef_access },
>> + { SYS_DESC(SYS_BRBINFINJ_EL1), undef_access },
>> + { SYS_DESC(SYS_BRBSRCINJ_EL1), undef_access },
>> + { SYS_DESC(SYS_BRBTGTINJ_EL1), undef_access },
>> + { SYS_DESC(SYS_BRBIDR0_EL1), undef_access },
>> +
>> { SYS_DESC(SYS_MDCCSR_EL0), trap_raz_wi },
>> { SYS_DESC(SYS_DBGDTR_EL0), trap_raz_wi },
>> // DBGDTR[TR]X_EL0 share the same encoding
>> --
>> 2.25.1
>>
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