linux-kernel - [PATCH] arm64: Move storage of idreg overrides into mmuoff section

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Message-Id: <20250130204614.64621-1-oliver.upton@linux.dev>
Date: Thu, 30 Jan 2025 12:46:15 -0800
From: Oliver Upton <oliver.upton@...ux.dev>
To: linux-arm-kernel@...ts.infradead.org
Cc: linux-kernel@...r.kernel.org,
	Catalin Marinas <catalin.marinas@....com>,
	Will Deacon <will@...nel.org>,
	Marc Zyngier <maz@...nel.org>,
	Mark Brown <broonie@...nel.org>,
	Ard Biesheuvel <ardb@...nel.org>,
	Joey Gouly <joey.gouly@....com>,
	James Morse <james.morse@....com>,
	Oliver Upton <oliver.upton@...ux.dev>,
	stable@...r.kernel.org,
	Moritz Fischer <moritzf@...gle.com>,
	Pedro Martelletto <martelletto@...gle.com>,
	Jon Masters <jonmasters@...gle.com>
Subject: [PATCH] arm64: Move storage of idreg overrides into mmuoff section

There are a few places where the idreg overrides are read w/ the MMU
off, for example the VHE and hVHE checks in __finalise_el2. And while
the infrastructure gets this _mostly_ right (i.e. does the appropriate
cache maintenance), the placement of the data itself is problematic and
could share a cache line with something else.

Depending on how unforgiving an implementation's handling of mismatched
attributes is, this could lead to data corruption. In one observed case,
the system_cpucaps shared a line with arm64_sw_feature_override and the
cpucaps got nuked after entering the hyp stub...

Even though only a few overrides are read without the MMU on, just throw
the whole lot into the mmuoff section and be done with it.

Cc: stable@...r.kernel.org # v5.15+
Tested-by: Moritz Fischer <moritzf@...gle.com>
Tested-by: Pedro Martelletto <martelletto@...gle.com>
Reported-by: Jon Masters <jonmasters@...gle.com>
Signed-off-by: Oliver Upton <oliver.upton@...ux.dev>
---
 arch/arm64/kernel/cpufeature.c | 25 ++++++++++++++-----------
 1 file changed, 14 insertions(+), 11 deletions(-)

diff --git a/arch/arm64/kernel/cpufeature.c b/arch/arm64/kernel/cpufeature.c
index d41128e37701..92506d9f90db 100644
--- a/arch/arm64/kernel/cpufeature.c
+++ b/arch/arm64/kernel/cpufeature.c
@@ -755,17 +755,20 @@ static const struct arm64_ftr_bits ftr_raz[] = {
 #define ARM64_FTR_REG(id, table)		\
 	__ARM64_FTR_REG_OVERRIDE(#id, id, table, &no_override)
 
-struct arm64_ftr_override id_aa64mmfr0_override;
-struct arm64_ftr_override id_aa64mmfr1_override;
-struct arm64_ftr_override id_aa64mmfr2_override;
-struct arm64_ftr_override id_aa64pfr0_override;
-struct arm64_ftr_override id_aa64pfr1_override;
-struct arm64_ftr_override id_aa64zfr0_override;
-struct arm64_ftr_override id_aa64smfr0_override;
-struct arm64_ftr_override id_aa64isar1_override;
-struct arm64_ftr_override id_aa64isar2_override;
-
-struct arm64_ftr_override arm64_sw_feature_override;
+#define DEFINE_FTR_OVERRIDE(name)					\
+	struct arm64_ftr_override __section(".mmuoff.data.read") name
+
+DEFINE_FTR_OVERRIDE(id_aa64mmfr0_override);
+DEFINE_FTR_OVERRIDE(id_aa64mmfr1_override);
+DEFINE_FTR_OVERRIDE(id_aa64mmfr2_override);
+DEFINE_FTR_OVERRIDE(id_aa64pfr0_override);
+DEFINE_FTR_OVERRIDE(id_aa64pfr1_override);
+DEFINE_FTR_OVERRIDE(id_aa64zfr0_override);
+DEFINE_FTR_OVERRIDE(id_aa64smfr0_override);
+DEFINE_FTR_OVERRIDE(id_aa64isar1_override);
+DEFINE_FTR_OVERRIDE(id_aa64isar2_override);
+
+DEFINE_FTR_OVERRIDE(arm64_sw_feature_override);
 
 static const struct __ftr_reg_entry {
 	u32			sys_id;

base-commit: 1dd3393696efba1598aa7692939bba99d0cffae3
-- 
2.39.5