[PATCH V3] arm64/cpufeature: Validate feature bits spacing in arm64_ftr_regs[]

[Anshuman Khandual]

arm64_feature_bits for a register in arm64_ftr_regs[] are in a descending
order as per their shift values. Validate that these features bits are
defined correctly and do not overlap with each other. This check protects
against any inadvertent erroneous changes to the register definitions.

Cc: Catalin Marinas <catalin.marinas@xxxxxxx>
Cc: Will Deacon <will@xxxxxxxxxx>
Cc: Suzuki K Poulose <suzuki.poulose@xxxxxxx>
Cc: Mark Brown <broonie@xxxxxxxxxx>
Cc: Mark Rutland <mark.rutland@xxxxxxx>
Cc: linux-arm-kernel@xxxxxxxxxxxxxxxxxxx
Cc: linux-kernel@xxxxxxxxxxxxxxx
Reviewed-by: Suzuki K Poulose <suzuki.poulose@xxxxxxx>
Signed-off-by: Anshuman Khandual <anshuman.khandual@xxxxxxx>
---
Applies on 5.8-rc4.

Changes in V3:

- Moved around some local variables per Suzuki

Changes in V2: (https://patchwork.kernel.org/patch/11635395/)

- Replaced WARN_ON() with WARN() dropping the conditional block per Suzuki

Changes in V1: (https://patchwork.kernel.org/patch/11606285/)

 arch/arm64/kernel/cpufeature.c | 47 +++++++++++++++++++++++++++++++---
 1 file changed, 44 insertions(+), 3 deletions(-)

diff --git a/arch/arm64/kernel/cpufeature.c b/arch/arm64/kernel/cpufeature.c
index 9fae0efc80c1..ddca88c660f6 100644
--- a/arch/arm64/kernel/cpufeature.c
+++ b/arch/arm64/kernel/cpufeature.c
@@ -697,11 +697,52 @@ static s64 arm64_ftr_safe_value(const struct arm64_ftr_bits *ftrp, s64 new,
 
 static void __init sort_ftr_regs(void)
 {
-	int i;
+	unsigned int i;
+
+	for (i = 0; i < ARRAY_SIZE(arm64_ftr_regs); i++) {
+		const struct arm64_ftr_reg *ftr_reg = arm64_ftr_regs[i].reg;
+		const struct arm64_ftr_bits *ftr_bits = ftr_reg->ftr_bits;
+		unsigned int j = 0;
+
+		/*
+		 * Features here must be sorted in descending order with respect
+		 * to their shift values and should not overlap with each other.
+		 */
+		for (; ftr_bits->width != 0; ftr_bits++, j++) {
+			unsigned int width = ftr_reg->ftr_bits[j].width;
+			unsigned int shift = ftr_reg->ftr_bits[j].shift;
+			unsigned int prev_shift;
+
+			WARN((shift  + width) > 64,
+				"%s has invalid feature at shift %d\n",
+				ftr_reg->name, shift);
+
+			/*
+			 * Skip the first feature. There is nothing to
+			 * compare against for now.
+			 */
+			if (j == 0)
+				continue;
 
-	/* Check that the array is sorted so that we can do the binary search */
-	for (i = 1; i < ARRAY_SIZE(arm64_ftr_regs); i++)
+			prev_shift = ftr_reg->ftr_bits[j - 1].shift;
+			WARN((shift + width) > prev_shift,
+				"%s has feature overlap at shift %d\n",
+				ftr_reg->name, shift);
+		}
+
+		/*
+		 * Skip the first register. There is nothing to
+		 * compare against for now.
+		 */
+		if (i == 0)
+			continue;
+		/*
+		 * Registers here must be sorted in ascending order with respect
+		 * to sys_id for subsequent binary search in get_arm64_ftr_reg()
+		 * to work correctly.
+		 */
 		BUG_ON(arm64_ftr_regs[i].sys_id < arm64_ftr_regs[i - 1].sys_id);
+	}
 }
 
 /*
-- 
2.20.1