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 --- include/linux/arm-smccc.h | 2 ++ virt/kvm/arm/psci.c | 2 +- 2 files changed, 3 insertions(+), 1 deletion(-)

diff --git a/include/linux/arm-smccc.h b/include/linux/arm-smccc.h index 080012a6f025..157e4a6a83f6 100644 --- a/include/linux/arm-smccc.h +++ b/include/linux/arm-smccc.h @@ -76,6 +76,8 @@ ARM_SMCCC_SMC_32, \ 0, 0x7fff)

+#define SMCCC_ARCH_WORKAROUND_RET_UNAFFECTED 1 + #ifndef __ASSEMBLY__

#include <linux/linkage.h> diff --git a/virt/kvm/arm/psci.c b/virt/kvm/arm/psci.c index 87927f7e1ee7..48fde38d64c3 100644 --- a/virt/kvm/arm/psci.c +++ b/virt/kvm/arm/psci.c @@ -408,7 +408,7 @@ int kvm_hvc_call_handler(struct kvm_vcpu *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;