Re: [PATCH 1/2] arm64: cpufeatures: Fix handling of CONFIG_CMDLINE for idreg overrides

[Marc Zyngier <maz@kernel.org>]

On Thu, 25 Feb 2021 12:59:20 +0000,
Will Deacon <will@kernel.org> wrote:
> 
> The built-in kernel commandline (CONFIG_CMDLINE) can be configured in
> three different ways:
> 
>   1. CMDLINE_FORCE: Use CONFIG_CMDLINE instead of any bootloader args
>   2. CMDLINE_EXTEND: Append the bootloader args to CONFIG_CMDLINE
>   3. CMDLINE_FROM_BOOTLOADER: Only use CONFIG_CMDLINE if there aren't
>      any bootloader args.
> 
> The early cmdline parsing to detect idreg overrides gets (2) and (3)
> slightly wrong: in the case of (2) the bootloader args are parsed first
> and in the case of (3) the CMDLINE is always parsed.
> 
> Fix these issues by moving the bootargs parsing out into a helper
> function and following the same logic as that used by the EFI stub.
> 
> Cc: Marc Zyngier <maz@kernel.org>
> Fixes: 33200303553d ("arm64: cpufeature: Add an early command-line cpufeature override facility")
> Signed-off-by: Will Deacon <will@kernel.org>
> ---
>  arch/arm64/kernel/idreg-override.c | 44 +++++++++++++++++-------------
>  1 file changed, 25 insertions(+), 19 deletions(-)
> 
> diff --git a/arch/arm64/kernel/idreg-override.c b/arch/arm64/kernel/idreg-override.c
> index dffb16682330..cc071712c6f9 100644
> --- a/arch/arm64/kernel/idreg-override.c
> +++ b/arch/arm64/kernel/idreg-override.c
> @@ -163,33 +163,39 @@ static __init void __parse_cmdline(const char *cmdline, bool parse_aliases)
>  	} while (1);
>  }
>  
> -static __init void parse_cmdline(void)
> +static __init const u8 *get_bootargs_cmdline(void)
>  {
> -	if (!IS_ENABLED(CONFIG_CMDLINE_FORCE)) {
> -		const u8 *prop;
> -		void *fdt;
> -		int node;
> +	const u8 *prop;
> +	void *fdt;
> +	int node;
>  
> -		fdt = get_early_fdt_ptr();
> -		if (!fdt)
> -			goto out;
> +	fdt = get_early_fdt_ptr();
> +	if (!fdt)
> +		return NULL;
>  
> -		node = fdt_path_offset(fdt, "/chosen");
> -		if (node < 0)
> -			goto out;
> +	node = fdt_path_offset(fdt, "/chosen");
> +	if (node < 0)
> +		return NULL;
>  
> -		prop = fdt_getprop(fdt, node, "bootargs", NULL);
> -		if (!prop)
> -			goto out;
> +	prop = fdt_getprop(fdt, node, "bootargs", NULL);
> +	if (!prop)
> +		return NULL;
>  
> -		__parse_cmdline(prop, true);
> +	return strlen(prop) ? prop : NULL;
> +}
>  
> -		if (!IS_ENABLED(CONFIG_CMDLINE_EXTEND))
> -			return;
> +static __init void parse_cmdline(void)
> +{
> +	const u8 *prop = get_bootargs_cmdline();
> +
> +	if (IS_ENABLED(CONFIG_CMDLINE_EXTEND) ||
> +	    IS_ENABLED(CONFIG_CMDLINE_FORCE) ||
> +	    !prop) {

The logic hurts, but I think I grok it now. The last term is actually
a reduction of

	(IS_ENABLED(CONFIG_CMDLINE_FROM_BOOTLOADER) && !prop)

and we know for sure that if none of the other two terms are true,
then CMDLINE_FROM_BOOTLOADER *must* be enabled.

> +		__parse_cmdline(CONFIG_CMDLINE, true);
>  	}
>  
> -out:
> -	__parse_cmdline(CONFIG_CMDLINE, true);
> +	if (!IS_ENABLED(CONFIG_CMDLINE_FORCE) && prop)
> +		__parse_cmdline(prop, true);
>  }
>  
>  /* Keep checkers quiet */

I don't think we need to backport anything to stable for the nokaslr
handling, do we?

Otherwise,

Reviewed-by: Marc Zyngier <maz@kernel.org>

Thanks,

	M.

-- 
Without deviation from the norm, progress is not possible.

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