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Wed, 21 Oct 2020 11:23:34 +0100 MIME-Version: 1.0 Date: Wed, 21 Oct 2020 11:23:34 +0100 From: Marc Zyngier To: Will Deacon Subject: Re: [PATCH 1/2] arm64: ARM_SMCCC_ARCH_WORKAROUND_1 doesn't return SMCCC_RET_NOT_REQUIRED In-Reply-To: <20201021075722.GA17230@willie-the-truck> References: <20201020214544.3206838-1-swboyd@chromium.org> <20201020214544.3206838-2-swboyd@chromium.org> <20201021075722.GA17230@willie-the-truck> User-Agent: Roundcube Webmail/1.4.9 Message-ID: X-Sender: maz@kernel.org X-SA-Exim-Connect-IP: 51.254.78.96 X-SA-Exim-Rcpt-To: will@kernel.org, swboyd@chromium.org, catalin.marinas@arm.com, linux-kernel@vger.kernel.org, linux-arm-kernel@lists.infradead.org, andre.przywara@arm.com, steven.price@arm.com, stable@vger.kernel.org X-SA-Exim-Mail-From: maz@kernel.org X-SA-Exim-Scanned: No (on disco-boy.misterjones.org); SAEximRunCond expanded to false X-CRM114-Version: 20100106-BlameMichelson ( TRE 0.8.0 (BSD) ) MR-646709E3 X-CRM114-CacheID: sfid-20201021_062338_446311_7772E229 X-CRM114-Status: GOOD ( 30.64 ) X-BeenThere: linux-arm-kernel@lists.infradead.org X-Mailman-Version: 2.1.29 Precedence: list List-Id: List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , Cc: Catalin Marinas , linux-kernel@vger.kernel.org, stable@vger.kernel.org, Steven Price , Andre Przywara , Stephen Boyd , linux-arm-kernel@lists.infradead.org Content-Transfer-Encoding: 7bit Content-Type: text/plain; charset="us-ascii"; Format="flowed" Sender: "linux-arm-kernel" Errors-To: linux-arm-kernel-bounces+linux-arm-kernel=archiver.kernel.org@lists.infradead.org On 2020-10-21 08:57, Will Deacon wrote: > On Tue, Oct 20, 2020 at 02:45:43PM -0700, Stephen Boyd wrote: >> According to the SMCCC spec (7.5.2 Discovery) the >> ARM_SMCCC_ARCH_WORKAROUND_1 function id only returns 0, 1, and >> SMCCC_RET_NOT_SUPPORTED corresponding to "workaround required", >> "workaround not required but implemented", and "who knows, you're on >> your own" respectively. For kvm hypercalls (hvc), we've implemented >> this >> function id to return SMCCC_RET_NOT_SUPPORTED, 1, and >> SMCCC_RET_NOT_REQUIRED. The SMCCC_RET_NOT_REQUIRED return value is not >> a >> thing for this function id, and is probably copy/pasted from the >> SMCCC_ARCH_WORKAROUND_2 function id that does support it. >> >> Clean this up by returning 0, 1, and SMCCC_RET_NOT_SUPPORTED >> appropriately. Changing this exposes the problem that >> spectre_v2_get_cpu_fw_mitigation_state() assumes a >> SMCCC_RET_NOT_SUPPORTED return value means we are vulnerable, but >> really >> it means we have no idea and should assume we can't do anything about >> mitigation. Put another way, it better be unaffected because it can't >> be >> mitigated in the firmware (in this case kvm) as the call isn't >> implemented! >> >> Cc: Andre Przywara >> Cc: Steven Price >> Cc: Marc Zyngier >> Cc: stable@vger.kernel.org >> Fixes: c118bbb52743 ("arm64: KVM: Propagate full Spectre v2 workaround >> state to KVM guests") >> Fixes: 73f381660959 ("arm64: Advertise mitigation of Spectre-v2, or >> lack thereof") >> Signed-off-by: Stephen Boyd >> --- >> >> This will require a slightly different backport to stable kernels, but >> at least it looks like this is a problem given that this return value >> isn't valid per the spec and we've been going around it by returning >> something invalid for some time. >> >> arch/arm64/kernel/proton-pack.c | 3 +-- >> arch/arm64/kvm/hypercalls.c | 2 +- >> 2 files changed, 2 insertions(+), 3 deletions(-) >> >> diff --git a/arch/arm64/kernel/proton-pack.c >> b/arch/arm64/kernel/proton-pack.c >> index 68b710f1b43f..00bd54f63f4f 100644 >> --- a/arch/arm64/kernel/proton-pack.c >> +++ b/arch/arm64/kernel/proton-pack.c >> @@ -149,10 +149,9 @@ static enum mitigation_state >> spectre_v2_get_cpu_fw_mitigation_state(void) >> case SMCCC_RET_SUCCESS: >> return SPECTRE_MITIGATED; >> case SMCCC_ARCH_WORKAROUND_RET_UNAFFECTED: >> + case SMCCC_RET_NOT_SUPPORTED: /* Good luck w/ the Gatekeeper of >> Gozer */ >> return SPECTRE_UNAFFECTED; > > Hmm, I'm not sure this is correct. The SMCCC spec is terrifically > unhelpful: > > NOT_SUPPORTED: > Either: > * None of the PEs in the system require firmware mitigation for > CVE-2017-5715. > * The system contains at least 1 PE affected by CVE-2017-5715 that > has no firmware > mitigation available. > * The firmware does not provide any information about whether > firmware mitigation is > required. > > so we can't tell whether the thing is vulnerable or not in this case, > and > have to assume that it is. > >> default: >> - fallthrough; >> - case SMCCC_RET_NOT_SUPPORTED: >> return SPECTRE_VULNERABLE; >> } >> } >> diff --git a/arch/arm64/kvm/hypercalls.c b/arch/arm64/kvm/hypercalls.c >> index 9824025ccc5c..868486957808 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 SPECTRE_UNAFFECTED: >> - val = SMCCC_RET_NOT_REQUIRED; >> + val = SMCCC_RET_NOT_SUPPORTED; > > Which means we need to return SMCCC_ARCH_WORKAROUND_RET_UNAFFECTED > here, I > suppose? Gahh, I keep mixing Spectre-v2 and WA2. Not good. I *think* the patch below is enough, but I need to give it a go... M. diff --git a/arch/arm64/kernel/proton-pack.c b/arch/arm64/kernel/proton-pack.c index 68b710f1b43f..3f417d6305ef 100644 --- a/arch/arm64/kernel/proton-pack.c +++ b/arch/arm64/kernel/proton-pack.c @@ -134,8 +134,6 @@ static enum mitigation_state spectre_v2_get_cpu_hw_mitigation_state(void) return SPECTRE_VULNERABLE; } -#define SMCCC_ARCH_WORKAROUND_RET_UNAFFECTED (1) - static enum mitigation_state spectre_v2_get_cpu_fw_mitigation_state(void) { int ret; @@ -148,7 +146,7 @@ static enum mitigation_state spectre_v2_get_cpu_fw_mitigation_state(void) switch (ret) { case SMCCC_RET_SUCCESS: return SPECTRE_MITIGATED; - case SMCCC_ARCH_WORKAROUND_RET_UNAFFECTED: + case SMCCC_RET_UNAFFECTED: return SPECTRE_UNAFFECTED; default: fallthrough; @@ -474,7 +472,7 @@ static enum mitigation_state spectre_v4_get_cpu_fw_mitigation_state(void) switch (ret) { case SMCCC_RET_SUCCESS: return SPECTRE_MITIGATED; - case SMCCC_ARCH_WORKAROUND_RET_UNAFFECTED: + case SMCCC_RET_UNAFFECTED: fallthrough; case SMCCC_RET_NOT_REQUIRED: return SPECTRE_UNAFFECTED; diff --git a/arch/arm64/kvm/hypercalls.c b/arch/arm64/kvm/hypercalls.c index 9824025ccc5c..792824de5d27 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 SPECTRE_UNAFFECTED: - val = SMCCC_RET_NOT_REQUIRED; + val = SMCCC_RET_UNAFFECTED; break; } break; diff --git a/include/linux/arm-smccc.h b/include/linux/arm-smccc.h index 885c9ffc835c..6b4902dde822 100644 --- a/include/linux/arm-smccc.h +++ b/include/linux/arm-smccc.h @@ -104,6 +104,7 @@ * Return codes defined in ARM DEN 0070A * ARM DEN 0070A is now merged/consolidated into ARM DEN 0028 C */ +#define SMCCC_RET_UNAFFECTED 1 #define SMCCC_RET_SUCCESS 0 #define SMCCC_RET_NOT_SUPPORTED -1 #define SMCCC_RET_NOT_REQUIRED -2 -- Jazz is not dead. It just smells funny... _______________________________________________ linux-arm-kernel mailing list linux-arm-kernel@lists.infradead.org http://lists.infradead.org/mailman/listinfo/linux-arm-kernel