linux-kernel - [PATCH v2 4/6] arm64: errata: Add QCOM_KRYO_2XX_GOLD to the spectre_bhb_firmware_mitigated

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Message-ID: <20241213165201.v2.4.Ia3dfc0afadbfbee81bb2efb0672262470973dd08@changeid>
Date: Fri, 13 Dec 2024 16:52:05 -0800
From: Douglas Anderson <dianders@...omium.org>
To: Catalin Marinas <catalin.marinas@....com>,
	Will Deacon <will@...nel.org>,
	Mark Rutland <mark.rutland@....com>
Cc: linux-arm-msm@...r.kernel.org,
	Jeffrey Hugo <quic_jhugo@...cinc.com>,
	Julius Werner <jwerner@...omium.org>,
	linux-arm-kernel@...ts.infradead.org,
	Roxana Bradescu <roxabee@...gle.com>,
	Trilok Soni <quic_tsoni@...cinc.com>,
	bjorn.andersson@....qualcomm.com,
	Douglas Anderson <dianders@...omium.org>,
	stable@...r.kernel.org,
	James Morse <james.morse@....com>,
	linux-kernel@...r.kernel.org
Subject: [PATCH v2 4/6] arm64: errata: Add QCOM_KRYO_2XX_GOLD to the spectre_bhb_firmware_mitigated_list

Qualcomm Kryo 200-series Gold cores appear to have a derivative of an
ARM Cortex A73 in them. Since A73 needs Spectre mitigation via
firmware then the Kyro 200-series Gold cores also should need Spectre
mitigation via firmware.

Unless devices with a Kryo 2XX gold core have a firmware that provides
ARM_SMCCC_ARCH_WORKAROUND_3 (which seems unlikely at the time this
patch is posted), this will make devices with these cores report that
they are vulnerable to Spectre BHB with no mitigation in place. This
patch will also cause them not to do a WARN splat at boot about an
unknown CPU ID and to stop trying to do a "loop" mitigation for these
cores which is (presumably) not reliable for them.

Fixes: 558c303c9734 ("arm64: Mitigate spectre style branch history side channels")
Cc: stable@...r.kernel.org
Signed-off-by: Douglas Anderson <dianders@...omium.org>
---
I don't really have any good way to test this patch but it seems
likely it's needed. If nothing else the claim is that that Qualcomm
Kyro 280 CPU is vulnerable [1] but I don't see any mitigations in the
kernel for it.

NOTE: presumably this patch won't actually do much on its own because
(I believe) it requires a firmware update (one adding
ARM_SMCCC_ARCH_WORKAROUND_3) to go with it.

[1] https://spectreattack.com/spectre.pdf

Changes in v2:
- Rebased / reworded QCOM_KRYO_2XX_GOLD patch

 arch/arm64/kernel/proton-pack.c | 1 +
 1 file changed, 1 insertion(+)

diff --git a/arch/arm64/kernel/proton-pack.c b/arch/arm64/kernel/proton-pack.c
index 04c3f0567999..3b179a1bf815 100644
--- a/arch/arm64/kernel/proton-pack.c
+++ b/arch/arm64/kernel/proton-pack.c
@@ -844,6 +844,7 @@ static unsigned long system_bhb_mitigations;
 static const struct midr_range spectre_bhb_firmware_mitigated_list[] = {
 	MIDR_ALL_VERSIONS(MIDR_CORTEX_A73),
 	MIDR_ALL_VERSIONS(MIDR_CORTEX_A75),
+	MIDR_ALL_VERSIONS(MIDR_QCOM_KRYO_2XX_GOLD),
 	{},
 };

-- 
2.47.1.613.gc27f4b7a9f-goog