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Donenfeld" Date: Thu, 6 Oct 2022 11:24:16 -0600 X-Gmail-Original-Message-ID: Message-ID: Subject: Re: [PATCH v3 3/5] treewide: use get_random_u32() when possible To: Christophe Leroy Content-Type: text/plain; charset="UTF-8" Content-Transfer-Encoding: quoted-printable X-Mailman-Approved-At: Fri, 07 Oct 2022 09:35:18 +1100 X-BeenThere: linuxppc-dev@lists.ozlabs.org X-Mailman-Version: 2.1.29 Precedence: list List-Id: Linux on PowerPC Developers Mail List List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , Cc: "linux-wireless@vger.kernel.org" , Ulf Hansson , "x86@kernel.org" , Jan Kara , Vignesh Raghavendra , "linux-doc@vger.kernel.org" , Peter Zijlstra , Catalin Marinas , Dave Hansen , "kernel-janitors@vger.kernel.org" , KP Singh , "dri-devel@lists.freedesktop.org" , "patches@lists.linux.dev" , "linux-mm@kvack.org" , Eric Dumazet , "netdev@vger.kernel.org" , "linux-mtd@lists.infradead.org" , "H . 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Bottomley" , Pablo Neira Ayuso , "linux-media@vger.kernel.org" , Marco Elver , Kees Cook , Yury Norov , Heiko Carstens , =?UTF-8?B?VG9rZSBIw7hpbGFuZC1Kw7hyZ2Vuc2Vu?= , "linux-um@lists.infradead.org" , "linux-mips@vger.kernel.org" , "linux-block@vger.kernel.org" , Richard Weinberger , Borislav Petkov , "linux-nvme@lists.infradead.org" , "loongarch@lists.linux.dev" , Jakub Kicinski , Thomas Gleixner , Andy Shevchenko , Johannes Berg , "linux-arm-kernel@lists.infradead.org" , Jens Axboe , "linux-mmc@vger.kernel.org" , Thomas Bogendoerfer , Theodore Ts'o , "linux-parisc@vger.kernel.org" , Greg Kroah-Hartman , "linux-usb@vger.kernel.org" , Florian Westphal , "linux-kernel@vger.kernel.org" , =?UTF-8?Q?Christoph_B=C3=B6hmwalder?= , Chuck Lever , "linux-crypto@vger.kernel.org" , Jan Kara , Thomas Graf , "linux-fsdevel@vger.kernel.org" , Andrew Morton , "linuxppc-dev@lists.ozlabs.org" , "David S . Miller" Errors-To: linuxppc-dev-bounces+linuxppc-dev=archiver.kernel.org@lists.ozlabs.org Sender: "Linuxppc-dev" 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 around > > 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 is > > just a wrapper around get_random_u32(). > > > > Reviewed-by: Kees Cook > > Acked-by: Toke H=C3=B8iland-J=C3=B8rgensen # for sch_cak= e > > 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/proces= s.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_s= pace) > > - 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. Jason