[PATCH] arm64: cpufeature: Check the override in __read_sysreg_by_encoding()

[Fuad Tabba <fuad.tabba@linux.dev>]

__read_sysreg_by_encoding() backs the capability checks a secondary
runs before its cpuinfo is stored, and folds an ID register override
into the value it reads without checking it against that CPU. A
secondary whose field is below an override the boot CPU accepted
passes verification and comes online without the feature.

Apply the override through arm64_ftr_reg_override(), as the cpuinfo
store does, so that it only applies where it is safe against that CPU's
value.

Fixes: b3341ae0efa2 ("arm64: cpufeature: Use IDreg override in __read_sysreg_by_encoding()")
Reported-by: Catalin Marinas <catalin.marinas@arm.com>
Link: https://lore.kernel.org/all/abwXl35xQ2ze1XwJ@arm.com/
Suggested-by: Suzuki K Poulose <suzuki.poulose@arm.com>
Signed-off-by: Fuad Tabba <fuad.tabba@linux.dev>
---

Notes:
    Based on v7.4-rc1 (6628e7d4c6b2), where arm64_ftr_reg_override() was
    added.

 arch/arm64/kernel/cpufeature.c | 9 +--------
 1 file changed, 1 insertion(+), 8 deletions(-)

diff --git a/arch/arm64/kernel/cpufeature.c b/arch/arm64/kernel/cpufeature.c
index 34c5c03c0c9b4..3980acdd6e1b7 100644
--- a/arch/arm64/kernel/cpufeature.c
+++ b/arch/arm64/kernel/cpufeature.c
@@ -1415,7 +1415,6 @@ EXPORT_SYMBOL_GPL(read_sanitised_ftr_reg);
  */
 u64 __read_sysreg_by_encoding(u32 sys_id)
 {
-	struct arm64_ftr_reg *regp;
 	u64 val;
 
 	switch (sys_id) {
@@ -1468,13 +1467,7 @@ u64 __read_sysreg_by_encoding(u32 sys_id)
 		return 0;
 	}
 
-	regp  = get_arm64_ftr_reg(sys_id);
-	if (regp) {
-		val &= ~regp->override->mask;
-		val |= (regp->override->val & regp->override->mask);
-	}
-
-	return val;
+	return arm64_ftr_reg_override(sys_id, val);
 }
 
 #include <linux/irqchip/arm-gic-v3.h>

base-commit: 6628e7d4c6b25c8d18f1345e3a20d21829aae7e4
-- 
2.47.3