linux-kernel - RE: [RFC PATCH v1 07/12] efi: Replace strstarts() by str_has

lists.openwall.net		lists / announce owl-users owl-dev john-users john-dev passwdqc-users yescrypt popa3d-users / oss-security kernel-hardening musl sabotage tlsify passwords / crypt-dev xvendor / Bugtraq Full-Disclosure linux-kernel linux-netdev linux-ext4 linux-hardening linux-cve-announce PHC
Open Source and information security mailing list archives

Hash Suite: Windows password security audit tool. GUI, reports in PDF.

[<prev] [next>] [<thread-prev] [thread-next>] [day] [month] [year] [list]

Message-ID: <4c251bcaf8234dd19ca0ecd0a756cf7f@AcuMS.aculab.com>
Date:   Fri, 11 Dec 2020 09:45:15 +0000
From:   David Laight <David.Laight@...LAB.COM>
To:     'Arvind Sankar' <nivedita@...m.mit.edu>,
        Ard Biesheuvel <ardb@...nel.org>
CC:     James Bottomley <James.Bottomley@...senpartnership.com>,
        "laniel_francis@...vacyrequired.com" 
        <laniel_francis@...vacyrequired.com>,
        linux-efi <linux-efi@...r.kernel.org>,
        Linux Kernel Mailing List <linux-kernel@...r.kernel.org>
Subject: RE: [RFC PATCH v1 07/12] efi: Replace strstarts() by
 str_has_prefix().

From: Arvind Sankar
> Sent: 10 December 2020 18:14
...
> I wasn't aware of str_has_prefix() at the time. It does seem useful to
> eliminate the duplication of the string literal, I like the
> skip_prefix() API suggestion, maybe even
> 
> 	bool str_skip_prefix(const char **s, const char *pfx)
> 	{
> 		size_t len = str_has_prefix(*s, pfx);
> 		*s += len;
> 		return !!len;
> 	}
> 	...
> 	if (str_skip_prefix(&option, prefix)) { ... }
> 
> to avoid the intermediate variable.

That'll generate horrid code - the 'option' variable has to be
repeatedly reloaded from memory (unless it is all inlined).

Perhaps the #define

#define str_skip_prefix(str, prefix) \
{( \
	size_t _pfx_len = strlen(prefix)); \
	memcmp(str, pfx, _pfx_len) ? 0 : ((str) += _pfx_len, 1); \
)}

There's probably something that'll let you use sizeof() instead
of strlen() for quoted strings (if only sizeof pfx != sizeof (char *)).

	David

-
Registered Address Lakeside, Bramley Road, Mount Farm, Milton Keynes, MK1 1PT, UK
Registration No: 1397386 (Wales)