linux-kernel - RE: [PATCH v4 10/24] crypto: x86/poly

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]

Date:   Tue, 22 Nov 2022 09:07:59 +0000
From:   David Laight <David.Laight@...LAB.COM>
To:     "'Elliott, Robert (Servers)'" <elliott@....com>,
        "Jason A. Donenfeld" <Jason@...c4.com>
CC:     "herbert@...dor.apana.org.au" <herbert@...dor.apana.org.au>,
        "davem@...emloft.net" <davem@...emloft.net>,
        "tim.c.chen@...ux.intel.com" <tim.c.chen@...ux.intel.com>,
        "ap420073@...il.com" <ap420073@...il.com>,
        "ardb@...nel.org" <ardb@...nel.org>,
        "ebiggers@...nel.org" <ebiggers@...nel.org>,
        "linux-crypto@...r.kernel.org" <linux-crypto@...r.kernel.org>,
        "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>
Subject: RE: [PATCH v4 10/24] crypto: x86/poly - limit FPU preemption

From: Elliott, Robert
> Sent: 22 November 2022 05:06
...
> Since enum doesn't guarantee any particular type, those variations
> upset the min() macro. min_t() is necessary to eliminate the
> compiler warning.

Yes, min() is fundamentally broken. min_t() isn't really a solution.
I think min() needs to include something like:

#define min(a, b) \
	__builtin_constant(b) && (b) + 0u <= MAX_INT ? \
		((a) < (int)(b) ? (a) : (int)(b)) : \
		...

So in the common case where 'b' is a small constant integer it
doesn't matter whether the is it signed or unsigned.

I might try compiling a kernel where min_t() does that instead
of the casts - just to see how many of the casts are actually
needed.

	David

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