From: Jason Gunthorpe <jgg@ziepe.ca>
To: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
Cc: Leon Romanovsky <leon@kernel.org>,
Peilin Ye <yepeilin.cs@gmail.com>,
Santosh Shilimkar <santosh.shilimkar@oracle.com>,
"David S. Miller" <davem@davemloft.net>,
Jakub Kicinski <kuba@kernel.org>,
Dan Carpenter <dan.carpenter@oracle.com>,
Arnd Bergmann <arnd@arndb.de>,
linux-kernel-mentees@lists.linuxfoundation.org,
netdev@vger.kernel.org, linux-rdma@vger.kernel.org,
rds-devel@oss.oracle.com, linux-kernel@vger.kernel.org
Subject: Re: [Linux-kernel-mentees] [PATCH net] rds: Prevent kernel-infoleak in rds_notify_queue_get()
Date: Fri, 31 Jul 2020 11:36:04 -0300 [thread overview]
Message-ID: <20200731143604.GF24045@ziepe.ca> (raw)
In-Reply-To: <20200731142148.GA1718799@kroah.com>
On Fri, Jul 31, 2020 at 04:21:48PM +0200, Greg Kroah-Hartman wrote:
> > The spec was updated in C11 to require zero'ing padding when doing
> > partial initialization of aggregates (eg = {})
> >
> > """if it is an aggregate, every member is initialized (recursively)
> > according to these rules, and any padding is initialized to zero
> > bits;"""
>
> But then why does the compilers not do this?
Do you have an example?
> > Considering we have thousands of aggregate initializers it
> > seems likely to me Linux also requires a compiler with this C11
> > behavior to operate correctly.
>
> Note that this is not an "operate correctly" thing, it is a "zero out
> stale data in structure paddings so that data will not leak to
> userspace" thing.
Yes, not being insecure is "operate correctly", IMHO :)
> > Does this patch actually fix anything? My compiler generates identical
> > assembly code in either case.
>
> What compiler version?
I tried clang 10 and gcc 9.3 for x86-64.
#include <string.h>
void test(void *out)
{
struct rds_rdma_notify {
unsigned long user_token;
unsigned int status;
} foo = {};
memcpy(out, &foo, sizeof(foo));
}
$ gcc -mno-sse2 -O2 -Wall -std=c99 t.c -S
test:
endbr64
movq $0, (%rdi)
movq $0, 8(%rdi)
ret
Just did this same test with gcc 4.4 and it also gave the same output..
Made it more complex with this:
struct rds_rdma_notify {
unsigned long user_token;
unsigned char status;
unsigned long user_token1;
unsigned char status1;
unsigned long user_token2;
unsigned char status2;
unsigned long user_token3;
unsigned char status3;
unsigned long user_token4;
unsigned char status4;
} foo;
And still got the same assembly vs memset on gcc 4.4.
I tried for a bit and didn't find a way to get even old gcc 4.4 to not
initialize the holes.
Jason
next prev parent reply other threads:[~2020-07-31 14:36 UTC|newest]
Thread overview: 30+ messages / expand[flat|nested] mbox.gz Atom feed top
2020-07-30 19:20 [Linux-kernel-mentees] [PATCH net] rds: Prevent kernel-infoleak in rds_notify_queue_get() Peilin Ye
2020-07-30 19:29 ` santosh.shilimkar
2020-07-31 4:53 ` Leon Romanovsky
2020-07-31 5:33 ` Greg Kroah-Hartman
2020-07-31 5:33 ` Greg Kroah-Hartman
[not found] ` <CAHp75Vdr2HC_ogNhBCxxGut9=Z6pQMFiA0w-268OQv+5unYOTg@mail.gmail.com>
2020-07-31 7:00 ` Leon Romanovsky
2020-07-31 7:05 ` Andy Shevchenko
2020-07-31 14:04 ` Jason Gunthorpe
2020-07-31 14:21 ` Greg Kroah-Hartman
2020-07-31 14:36 ` Jason Gunthorpe [this message]
2020-07-31 17:19 ` Greg Kroah-Hartman
2020-07-31 18:27 ` Jason Gunthorpe
2020-08-01 8:00 ` Dan Carpenter
2020-08-01 14:40 ` Jason Gunthorpe
2020-08-03 9:34 ` Dan Carpenter
2020-08-01 5:38 ` Leon Romanovsky
2020-08-02 22:10 ` Jason Gunthorpe
2020-08-02 22:23 ` Joe Perches
2020-08-02 22:28 ` Jason Gunthorpe
2020-08-02 22:45 ` Joe Perches
2020-08-03 4:58 ` Leon Romanovsky
2020-08-03 23:06 ` Jason Gunthorpe
2020-08-08 22:57 ` Jack Leadford
2020-08-09 7:04 ` Leon Romanovsky
2020-08-14 17:07 ` Jason Gunthorpe
2020-07-31 9:59 ` Dan Carpenter
2020-07-31 11:14 ` Håkon Bugge
2020-07-31 11:59 ` Greg Kroah-Hartman
2020-07-31 12:03 ` Håkon Bugge
2020-07-31 23:54 ` David Miller
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