linux-kernel - Re: [PATCH 1/3] lib: early_string: allow early usage of some string functions

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Date:   Fri, 30 Apr 2021 10:47:39 +0200
From:   Christophe Leroy <christophe.leroy@...roup.eu>
To:     Daniel Walker <danielwa@...co.com>, linuxppc-dev@...ts.ozlabs.org,
        x86@...nel.org, Andrew Morton <akpm@...ux-foundation.org>
Cc:     xe-linux-external@...co.com, linux-kernel@...r.kernel.org
Subject: Re: [PATCH 1/3] lib: early_string: allow early usage of some string
 functions



Le 30/04/2021 à 06:22, Daniel Walker a écrit :
> This systems allows some string functions to be moved into
> lib/early_string.c and they will be prepended with "early_" and compiled
> without debugging like KASAN.
> 
> This is already done on x86 for,
> "AMD Secure Memory Encryption (SME) support"
> 
> and on powerpc prom_init.c , and EFI's libstub.
> 
> The AMD memory feature disabled KASAN for all string functions, and
> prom_init.c and efi libstub implement their own versions of the
> functions.
> 
> This implementation allows sharing of the string functions without
> removing the debugging features for the whole system.

This looks good. I prefer that rather than the way you proposed to do it two years ago.

Only one problem, see below.

> +size_t strlcat(char *dest, const char *src, size_t count)
> +{
> +	size_t dsize = strlen(dest);
> +	size_t len = strlen(src);
> +	size_t res = dsize + len;
> +
> +	/* This would be a bug */
> +	BUG_ON(dsize >= count);

powerpc is not ready to handle BUG_ON() in when in prom_init.

Can you do:

#ifndef __EARLY_STRING_ENABLED
	BUG_ON(dsize >= count);
#endif


> +
> +	dest += dsize;
> +	count -= dsize;
> +	if (len >= count)
> +		len = count-1;
> +	memcpy(dest, src, len);
> +	dest[len] = 0;
> +	return res;
> +}
> +EXPORT_SYMBOL(strlcat);
> +#endif
> +