From mboxrd@z Thu Jan 1 00:00:00 1970 Received: from smtp.kernel.org (aws-us-west-2-korg-mail-1.web.codeaurora.org [10.30.226.201]) (using TLSv1.2 with cipher ECDHE-RSA-AES256-GCM-SHA384 (256/256 bits)) (No client certificate requested) by smtp.subspace.kernel.org (Postfix) with ESMTPS id 13C117F; Thu, 6 Oct 2022 23:37:00 +0000 (UTC) Received: by smtp.kernel.org (Postfix) with ESMTPSA id 60F64C433B5; Thu, 6 Oct 2022 23:37:00 +0000 (UTC) Authentication-Results: smtp.kernel.org; dkim=pass (1024-bit key) header.d=zx2c4.com header.i=@zx2c4.com header.b="IOQ1bXhF" DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=zx2c4.com; s=20210105; t=1665099413; h=from:from:reply-to:subject:subject:date:date:message-id:message-id: to:to:cc:cc:mime-version:mime-version:content-type:content-type: content-transfer-encoding:content-transfer-encoding: in-reply-to:in-reply-to:references:references; bh=eDWvYu+uSvuLU1D2yrcps4Uxg3s4afpQR1DZP1HAENk=; b=IOQ1bXhFd3q9+RqlaN9MoWoMb9hyeq0A9ZZHsjT7H7aJth5PyzgIFsO5RZ+IGkqpoVM4vs G1fhQ2wIq1VD89DBIQN9w7YwWxcZC7kUxAooqITvAEdpg/3zs8L5I8+aGBoP4EPhTcYjjM 7a1SFu0rQgOf0f04kGQaSuHs/qYIRR4= Received: by mail.zx2c4.com (ZX2C4 Mail Server) with ESMTPSA id 86176e06 (TLSv1.3:TLS_AES_256_GCM_SHA384:256:NO); Thu, 6 Oct 2022 23:36:53 +0000 (UTC) Received: by mail-vs1-f49.google.com with SMTP id k6so3514171vsc.8; Thu, 06 Oct 2022 16:36:53 -0700 (PDT) X-Gm-Message-State: ACrzQf2yXZgPAGV5FzTZ7A9fNladrkKi6Mpj9LnV22DTU6KjjNGurEiC UQaJsoVlWQCYGRX4JW/weQHkdD7XOW+NlmsE/9Y= X-Google-Smtp-Source: AMsMyM5tvZWHSrcOLtkY/lX0Q7Qvr/oXlGj5vIRT4adjylKOfvaHnErU8AKkQNdqtGo/HZJDgntpViQRNpApZtsIptY= X-Received: by 2002:a05:6102:2908:b0:398:ac40:d352 with SMTP id cz8-20020a056102290800b00398ac40d352mr1292105vsb.55.1665099409449; Thu, 06 Oct 2022 16:36:49 -0700 (PDT) Precedence: bulk X-Mailing-List: patches@lists.linux.dev List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 Received: by 2002:ab0:6ed0:0:b0:3d9:6dfd:499 with HTTP; Thu, 6 Oct 2022 16:36:48 -0700 (PDT) In-Reply-To: <6396875c-146a-acf5-dd9e-7f93ba1b4bc3@csgroup.eu> References: <20221006165346.73159-1-Jason@zx2c4.com> <20221006165346.73159-4-Jason@zx2c4.com> <848ed24c-13ef-6c38-fd13-639b33809194@csgroup.eu> <6396875c-146a-acf5-dd9e-7f93ba1b4bc3@csgroup.eu> From: "Jason A. Donenfeld" Date: Thu, 6 Oct 2022 17:36:48 -0600 X-Gmail-Original-Message-ID: Message-ID: Subject: Re: [PATCH v3 3/5] treewide: use get_random_u32() when possible To: Christophe Leroy Cc: "linux-kernel@vger.kernel.org" , "patches@lists.linux.dev" , Andreas Noever , Andrew Morton , Andy Shevchenko , Borislav Petkov , Catalin Marinas , =?UTF-8?Q?Christoph_B=C3=B6hmwalder?= , Christoph Hellwig , Daniel Borkmann , Dave Airlie , Dave Hansen , "David S . Miller" , Eric Dumazet , Florian Westphal , Greg Kroah-Hartman , "H . Peter Anvin" , Heiko Carstens , Helge Deller , Herbert Xu , Huacai Chen , Hugh Dickins , Jakub Kicinski , "James E . J . Bottomley" , Jan Kara , Jason Gunthorpe , Jens Axboe , Johannes Berg , Jonathan Corbet , Jozsef Kadlecsik , KP Singh , Kees Cook , Marco Elver , Mauro Carvalho Chehab , Michael Ellerman , Pablo Neira Ayuso , Paolo Abeni , Peter Zijlstra , Richard Weinberger , Russell King , "Theodore Ts'o" , Thomas Bogendoerfer , Thomas Gleixner , Thomas Graf , Ulf Hansson , Vignesh Raghavendra , WANG Xuerui , Will Deacon , Yury Norov , "dri-devel@lists.freedesktop.org" , "kasan-dev@googlegroups.com" , "kernel-janitors@vger.kernel.org" , "linux-arm-kernel@lists.infradead.org" , "linux-block@vger.kernel.org" , "linux-crypto@vger.kernel.org" , "linux-doc@vger.kernel.org" , "linux-fsdevel@vger.kernel.org" , "linux-media@vger.kernel.org" , "linux-mips@vger.kernel.org" , "linux-mm@kvack.org" , "linux-mmc@vger.kernel.org" , "linux-mtd@lists.infradead.org" , "linux-nvme@lists.infradead.org" , "linux-parisc@vger.kernel.org" , "linux-rdma@vger.kernel.org" , "linux-s390@vger.kernel.org" , "linux-um@lists.infradead.org" , "linux-usb@vger.kernel.org" , "linux-wireless@vger.kernel.org" , "linuxppc-dev@lists.ozlabs.org" , "loongarch@lists.linux.dev" , "netdev@vger.kernel.org" , "sparclinux@vger.kernel.org" , "x86@kernel.org" , =?UTF-8?B?VG9rZSBIw7hpbGFuZC1Kw7hyZ2Vuc2Vu?= , Chuck Lever , Jan Kara Content-Type: text/plain; charset="UTF-8" Content-Transfer-Encoding: quoted-printable On 10/6/22, Christophe Leroy wrote: > > > Le 06/10/2022 =C3=A0 19:31, Christophe Leroy a =C3=A9crit : >> >> >> Le 06/10/2022 =C3=A0 19:24, Jason A. Donenfeld a =C3=A9crit : >>> Hi Christophe, >>> >>> On Thu, Oct 6, 2022 at 11:21 AM Christophe Leroy >>> wrote: >>>> Le 06/10/2022 =C3=A0 18:53, Jason A. Donenfeld a =C3=A9crit : >>>>> The prandom_u32() function has been a deprecated inline wrapper aroun= d >>>>> get_random_u32() for several releases now, and compiles down to the >>>>> exact same code. Replace the deprecated wrapper with a direct call to >>>>> the real function. The same also applies to get_random_int(), which i= s >>>>> just a wrapper around get_random_u32(). >>>>> >>>>> Reviewed-by: Kees Cook >>>>> Acked-by: Toke H=C3=B8iland-J=C3=B8rgensen # for sch_c= ake >>>>> Acked-by: Chuck Lever # for nfsd >>>>> Reviewed-by: Jan Kara # for ext4 >>>>> Signed-off-by: Jason A. Donenfeld >>>>> --- >>>> >>>>> diff --git a/arch/powerpc/kernel/process.c >>>>> b/arch/powerpc/kernel/process.c >>>>> index 0fbda89cd1bb..9c4c15afbbe8 100644 >>>>> --- a/arch/powerpc/kernel/process.c >>>>> +++ b/arch/powerpc/kernel/process.c >>>>> @@ -2308,6 +2308,6 @@ void notrace __ppc64_runlatch_off(void) >>>>> unsigned long arch_align_stack(unsigned long sp) >>>>> { >>>>> if (!(current->personality & ADDR_NO_RANDOMIZE) && >>>>> randomize_va_space) >>>>> - sp -=3D get_random_int() & ~PAGE_MASK; >>>>> + sp -=3D get_random_u32() & ~PAGE_MASK; >>>>> return sp & ~0xf; >>>> >>>> Isn't that a candidate for prandom_u32_max() ? >>>> >>>> Note that sp is deemed to be 16 bytes aligned at all time. >>> >>> Yes, probably. It seemed non-trivial to think about, so I didn't. But >>> let's see here... maybe it's not too bad: >>> >>> If PAGE_MASK is always ~(PAGE_SIZE-1), then ~PAGE_MASK is >>> (PAGE_SIZE-1), so prandom_u32_max(PAGE_SIZE) should yield the same >>> thing? Is that accurate? And holds across platforms (this comes up a >>> few places)? If so, I'll do that for a v4. >>> >> >> On powerpc it is always (from arch/powerpc/include/asm/page.h) : >> >> /* >> * Subtle: (1 << PAGE_SHIFT) is an int, not an unsigned long. So if we >> * assign PAGE_MASK to a larger type it gets extended the way we want >> * (i.e. with 1s in the high bits) >> */ >> #define PAGE_MASK (~((1 << PAGE_SHIFT) - 1)) >> >> #define PAGE_SIZE (1UL << PAGE_SHIFT) >> >> >> So it would work I guess. > > But taking into account that sp must remain 16 bytes aligned, would it > be better to do something like ? > > sp -=3D prandom_u32_max(PAGE_SIZE >> 4) << 4; > > return sp; Does this assume that sp is already aligned at the beginning of the function? I'd assume from the function's name that this isn't the case? Jason