linux-kernel - RE: [PATCH] x86/entry/64: randomize kernel stack offset upon syscall

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: <e4fbad8c51284a0583b98c52de4a207d@AcuMS.aculab.com>
Date:   Fri, 3 May 2019 16:40:53 +0000
From:   David Laight <David.Laight@...LAB.COM>
To:     "'Reshetova, Elena'" <elena.reshetova@...el.com>,
        Ingo Molnar <mingo@...nel.org>
CC:     Andy Lutomirski <luto@...nel.org>, Theodore Ts'o <tytso@....edu>,
        "Eric Biggers" <ebiggers3@...il.com>,
        "ebiggers@...gle.com" <ebiggers@...gle.com>,
        "herbert@...dor.apana.org.au" <herbert@...dor.apana.org.au>,
        Peter Zijlstra <peterz@...radead.org>,
        "keescook@...omium.org" <keescook@...omium.org>,
        Daniel Borkmann <daniel@...earbox.net>,
        "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
        "jpoimboe@...hat.com" <jpoimboe@...hat.com>,
        "jannh@...gle.com" <jannh@...gle.com>,
        "Perla, Enrico" <enrico.perla@...el.com>,
        "mingo@...hat.com" <mingo@...hat.com>,
        "bp@...en8.de" <bp@...en8.de>,
        "tglx@...utronix.de" <tglx@...utronix.de>,
        "gregkh@...uxfoundation.org" <gregkh@...uxfoundation.org>,
        "Edgecombe, Rick P" <rick.p.edgecombe@...el.com>,
        Linus Torvalds <torvalds@...ux-foundation.org>,
        Peter Zijlstra <a.p.zijlstra@...llo.nl>
Subject: RE: [PATCH] x86/entry/64: randomize kernel stack offset upon syscall

From: Reshetova, Elena
> Sent: 03 May 2019 17:17
...
> rdrand (calling every 8 syscalls): Simple syscall: 0.0795 microseconds

You could try something like:
	u64 rand_val = cpu_var->syscall_rand

	while (unlikely(rand_val == 0))
		rand_val = rdrand64();

	stack_offset = rand_val & 0xff;
	rand_val >>= 6;
	if (likely(rand_val >= 4))
		cpu_var->syscall_rand = rand_val;
	else
		cpu_var->syscall_rand = rdrand64();

	return stack_offset;

That gives you 10 system calls per rdrand instruction
and mostly takes the latency out of line.

	David

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