| Message ID | 20201103201526.372590-1-swboyd@chromium.org |
|---|---|
| State | New |
| Headers | show |
| Series | [5.9] KVM: arm64: ARM_SMCCC_ARCH_WORKAROUND_1 doesn't return SMCCC_RET_NOT_REQUIRED | expand |
On Tue, Nov 03, 2020 at 12:15:26PM -0800, Stephen Boyd wrote: > 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> > --- > arch/arm64/kvm/hypercalls.c | 2 +- > include/linux/arm-smccc.h | 2 ++ > 2 files changed, 3 insertions(+), 1 deletion(-) Thanks for both of these, now queued up. greg k-h
diff --git a/arch/arm64/kvm/hypercalls.c b/arch/arm64/kvm/hypercalls.c index 550dfa3e53cd..b8e7f6c4524f 100644 --- a/arch/arm64/kvm/hypercalls.c +++ b/arch/arm64/kvm/hypercalls.c @@ -31,7 +31,7 @@ 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; diff --git a/include/linux/arm-smccc.h b/include/linux/arm-smccc.h index 15c706fb0a37..0e50ba3e88d7 100644 --- 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, \
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> --- arch/arm64/kvm/hypercalls.c | 2 +- include/linux/arm-smccc.h | 2 ++ 2 files changed, 3 insertions(+), 1 deletion(-)