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SubjectRe: [PATCH] arm64/cpufeature: Validate feature bits spacing in arm64_ftr_regs[]
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On 06/16/2020 03:25 AM, Anshuman Khandual wrote:
> 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@arm.com>
> Cc: Will Deacon <will@kernel.org>
> Cc: Suzuki K Poulose <suzuki.poulose@arm.com>
> Cc: Mark Brown <broonie@kernel.org>
> Cc: Mark Rutland <mark.rutland@arm.com>
> Cc: linux-arm-kernel@lists.infradead.org
> Cc: linux-kernel@vger.kernel.org
> Signed-off-by: Anshuman Khandual <anshuman.khandual@arm.com>
> ---
> Applies on 5.8-rc1.
>
> arch/arm64/kernel/cpufeature.c | 45 +++++++++++++++++++++++++++++++---
> 1 file changed, 42 insertions(+), 3 deletions(-)
>
> diff --git a/arch/arm64/kernel/cpufeature.c b/arch/arm64/kernel/cpufeature.c
> index 4ae41670c2e6..2270eda9a7fb 100644
> --- a/arch/arm64/kernel/cpufeature.c
> +++ b/arch/arm64/kernel/cpufeature.c
> @@ -697,11 +697,50 @@ static s64 arm64_ftr_safe_value(const struct arm64_ftr_bits *ftrp, s64 new,
>
> static void __init sort_ftr_regs(void)
> {
> - int i;
> + const struct arm64_ftr_reg *ftr_reg;
> + const struct arm64_ftr_bits *ftr_bits;
> + unsigned int i, j, width, shift, prev_shift;
> +
> + for (i = 0; i < ARRAY_SIZE(arm64_ftr_regs); i++) {
> + /*
> + * Features here must be sorted in descending order with respect
> + * to their shift values and should not overlap with each other.
> + */
> + ftr_reg = arm64_ftr_regs[i].reg;
> + for (ftr_bits = ftr_reg->ftr_bits, j = 0;
> + ftr_bits->width != 0; ftr_bits++, j++) {
> + if (WARN_ON(ftr_bits->shift + ftr_bits->width > 64))
> + pr_err("%s has invalid feature at shift %d\n",
> + ftr_reg->name, ftr_bits->shift);

nit:

WARN((ftr_bits->shift + ftr_bits->width) > 64,
"%s......);?

> +
> + /*
> + * Skip the first feature. There is nothing to
> + * compare against for now.
> + */
> + if (j == 0)
> + continue;
> +
> + prev_shift = ftr_reg->ftr_bits[j - 1].shift;
> + width = ftr_reg->ftr_bits[j].width;
> + shift = ftr_reg->ftr_bits[j].shift;
> + if (WARN_ON(prev_shift < shift + width))
> + pr_err("%s has feature overlap at shift %d\n",
> + ftr_reg->name, ftr_bits->shift);

same as above ?

> + }
>
> - /* Check that the array is sorted so that we can do the binary search */
> - for (i = 1; i < ARRAY_SIZE(arm64_ftr_regs); i++)
> + /*
> + * Skip the first register. There is nothing to
> + * compare against for now.
> + */
> + if (i == 0)
> + continue;

You are starting at 1 already, so you may skip this check.

> + /*
> + * 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);
> + }
> }
>
> /*

Otherwise looks good to me.

Suzuki

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