Date: Tue, 26 Jul 2016 09:40:36 -0700 From: Kees Cook <keescook@...omium.org> To: Jason Cooper <jason@...edaemon.net> Cc: "Roberts, William C" <william.c.roberts@...el.com>, linux-mm@...r.kernel.org, LKML <linux-kernel@...r.kernel.org>, "kernel-hardening@...ts.openwall.com" <kernel-hardening@...ts.openwall.com>, Russell King - ARM Linux <linux@....linux.org.uk>, Andrew Morton <akpm@...ux-foundation.org>, "Theodore Ts'o" <tytso@....edu>, Arnd Bergmann <arnd@...db.de>, Greg KH <gregkh@...uxfoundation.org>, Catalin Marinas <catalin.marinas@....com>, Will Deacon <will.deacon@....com>, Ralf Baechle <ralf@...ux-mips.org>, "benh@...nel.crashing.org" <benh@...nel.crashing.org>, Paul Mackerras <paulus@...ba.org>, Michael Ellerman <mpe@...erman.id.au>, "David S. Miller" <davem@...emloft.net>, Thomas Gleixner <tglx@...utronix.de>, Ingo Molnar <mingo@...hat.com>, "H. Peter Anvin" <hpa@...or.com>, "x86@...nel.org" <x86@...nel.org>, Al Viro <viro@...iv.linux.org.uk>, Nick Kralevich <nnk@...gle.com>, Jeffrey Vander Stoep <jeffv@...gle.com>, Mark Salyzyn <salyzyn@...roid.com>, Daniel Cashman <dcashman@...roid.com> Subject: Re: [RFC patch 1/6] random: Simplify API for random address requests On Tue, Jul 26, 2016 at 8:55 AM, Jason Cooper <jason@...edaemon.net> wrote: > On Mon, Jul 25, 2016 at 09:44:27PM -0700, Kees Cook wrote: >> On Mon, Jul 25, 2016 at 8:01 PM, Jason Cooper <jason@...edaemon.net> wrote: >> > To date, all callers of randomize_range() have set the length to 0, and >> > check for a zero return value. For the current callers, the only way >> > to get zero returned is if end <= start. Since they are all adding a >> > constant to the start address, this is unnecessary. >> > >> > We can remove a bunch of needless checks by simplifying the API to do >> > just what everyone wants, return an address between [start, start + >> > range]. >> > >> > While we're here, s/get_random_int/get_random_long/. No current call >> > site is adversely affected by get_random_int(), since all current range >> > requests are < MAX_UINT. However, we should match caller expectations >> > to avoid coming up short (ha!) in the future. >> > >> > Signed-off-by: Jason Cooper <jason@...edaemon.net> >> > --- >> > drivers/char/random.c | 17 ++++------------- >> > include/linux/random.h | 2 +- >> > 2 files changed, 5 insertions(+), 14 deletions(-) >> > >> > diff --git a/drivers/char/random.c b/drivers/char/random.c >> > index 0158d3bff7e5..1251cb2cbab2 100644 >> > --- a/drivers/char/random.c >> > +++ b/drivers/char/random.c >> > @@ -1822,22 +1822,13 @@ unsigned long get_random_long(void) >> > EXPORT_SYMBOL(get_random_long); >> > >> > /* >> > - * randomize_range() returns a start address such that >> > - * >> > - * [...... <range> .....] >> > - * start end >> > - * >> > - * a <range> with size "len" starting at the return value is inside in the >> > - * area defined by [start, end], but is otherwise randomized. >> > + * randomize_addr() returns a page aligned address within [start, start + >> > + * range] >> > */ >> > unsigned long >> > -randomize_range(unsigned long start, unsigned long end, unsigned long len) >> > +randomize_addr(unsigned long start, unsigned long range) >> >> Also, this series isn't bisectable since randomize_range gets removed >> here before the callers are updated. Perhaps add a macro that calls >> randomize_addr with a BUG_ON for len != 0? (And then remove it in the >> last patch?) > > No, I was thinking just add randomize_addr() in the first patch, convert > all the callers, then the last patch would remove randomize_range(). > > That way the last patch can be a cleanup in a later merge window if > needed. That works too! :) -Kees -- Kees Cook Chrome OS & Brillo Security
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