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    Subject[PATCH 5.9 073/255] KVM: arm64: ARM_SMCCC_ARCH_WORKAROUND_1 doesnt return SMCCC_RET_NOT_REQUIRED
    Date
    From: Stephen Boyd <swboyd@chromium.org>

    commit 1de111b51b829bcf01d2e57971f8fd07a665fa3f upstream.

    According to the SMCCC spec[1](7.5.2 Discovery) the
    ARM_SMCCC_ARCH_WORKAROUND_1 function id only returns 0, 1, and
    SMCCC_RET_NOT_SUPPORTED.

    0 is "workaround required and safe to call this function"
    1 is "workaround not required but safe to call this function"
    SMCCC_RET_NOT_SUPPORTED is "might be vulnerable or might not be, who knows, I give up!"

    SMCCC_RET_NOT_SUPPORTED might as well mean "workaround required, except
    calling this function may not work because it isn't implemented in some
    cases". Wonderful. We map this SMC call to

    0 is SPECTRE_MITIGATED
    1 is SPECTRE_UNAFFECTED
    SMCCC_RET_NOT_SUPPORTED is SPECTRE_VULNERABLE

    For KVM hypercalls (hvc), we've implemented this function id to return
    SMCCC_RET_NOT_SUPPORTED, 0, and SMCCC_RET_NOT_REQUIRED. One of those
    isn't supposed to be there. Per the code we call
    arm64_get_spectre_v2_state() to figure out what to return for this
    feature discovery call.

    0 is SPECTRE_MITIGATED
    SMCCC_RET_NOT_REQUIRED is SPECTRE_UNAFFECTED
    SMCCC_RET_NOT_SUPPORTED is SPECTRE_VULNERABLE

    Let's clean this up so that KVM tells the guest this mapping:

    0 is SPECTRE_MITIGATED
    1 is SPECTRE_UNAFFECTED
    SMCCC_RET_NOT_SUPPORTED is SPECTRE_VULNERABLE

    Note: SMCCC_RET_NOT_AFFECTED is 1 but isn't part of the SMCCC spec

    Fixes: c118bbb52743 ("arm64: KVM: Propagate full Spectre v2 workaround state to KVM guests")
    Signed-off-by: Stephen Boyd <swboyd@chromium.org>
    Acked-by: Marc Zyngier <maz@kernel.org>
    Acked-by: Will Deacon <will@kernel.org>
    Cc: Andre Przywara <andre.przywara@arm.com>
    Cc: Steven Price <steven.price@arm.com>
    Cc: Marc Zyngier <maz@kernel.org>
    Cc: stable@vger.kernel.org
    Link: https://developer.arm.com/documentation/den0028/latest [1]
    Link: https://lore.kernel.org/r/20201023154751.1973872-1-swboyd@chromium.org
    Signed-off-by: Will Deacon <will@kernel.org>
    Signed-off-by: Stephen Boyd <swboyd@chromium.org>
    Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
    ---
    arch/arm64/kvm/hypercalls.c | 2 +-
    include/linux/arm-smccc.h | 2 ++
    2 files changed, 3 insertions(+), 1 deletion(-)

    --- a/arch/arm64/kvm/hypercalls.c
    +++ b/arch/arm64/kvm/hypercalls.c
    @@ -31,7 +31,7 @@ int kvm_hvc_call_handler(struct kvm_vcpu
    val = SMCCC_RET_SUCCESS;
    break;
    case KVM_BP_HARDEN_NOT_REQUIRED:
    - val = SMCCC_RET_NOT_REQUIRED;
    + val = SMCCC_ARCH_WORKAROUND_RET_UNAFFECTED;
    break;
    }
    break;
    --- a/include/linux/arm-smccc.h
    +++ b/include/linux/arm-smccc.h
    @@ -86,6 +86,8 @@
    ARM_SMCCC_SMC_32, \
    0, 0x7fff)

    +#define SMCCC_ARCH_WORKAROUND_RET_UNAFFECTED 1
    +
    /* Paravirtualised time calls (defined by ARM DEN0057A) */
    #define ARM_SMCCC_HV_PV_TIME_FEATURES \
    ARM_SMCCC_CALL_VAL(ARM_SMCCC_FAST_CALL, \

    \
     
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