From: "H. Peter Anvin" <hpa@zytor.com>
To: Alexei Starovoitov <ast@plumgrid.com>,
Eric Dumazet <eric.dumazet@gmail.com>
Cc: "David S. Miller" <davem@davemloft.net>,
Eric Dumazet <edumazet@google.com>,
Daniel Borkmann <dborkman@redhat.com>,
Heiko Carstens <heiko.carstens@de.ibm.com>,
Network Development <netdev@vger.kernel.org>
Subject: Re: [PATCH net] net: filter: x86: fix JIT address randomization
Date: Tue, 13 May 2014 14:28:55 -0700 [thread overview]
Message-ID: <53728E97.6030400@zytor.com> (raw)
In-Reply-To: <CAMEtUuxLbDpkxJ4fORRdsJ36vBiidBwA0SVAwvmDHEpPmhTA2Q@mail.gmail.com>
On 05/13/2014 01:34 PM, Alexei Starovoitov wrote:
>>
>> The argument of not having code ending on (or being very close of) page
>> boundary seems orthogonal to this bug fix.
>
> Gotta pick some number... page/2 seems good enough to have
> large range for prandom() to choose and better performance.
> Another alternative is to do min(…, PAGE_SIZE - sizeof(*header)),
> but that is harder to understand.
>
The latter is correct by construction, and thus doesn't end up with the
question "what is going on here" or has hidden failure conditions.
> Also just realized that I miscalculated the breaking point:
> "If prandom_u32() % hole selects a number >= 4096, then kernel will crash"
> it should read: "… >= 4092 ..."
> since sizeof(*header) needs to be accounted for.
No, it should read PAGE_SIZE - sizeof(*header) if anything.
-hpa
next prev parent reply other threads:[~2014-05-13 21:29 UTC|newest]
Thread overview: 6+ messages / expand[flat|nested] mbox.gz Atom feed top
2014-05-13 18:53 [PATCH net] net: filter: x86: fix JIT address randomization Alexei Starovoitov
2014-05-13 20:23 ` Eric Dumazet
2014-05-13 20:34 ` Alexei Starovoitov
2014-05-13 21:28 ` H. Peter Anvin [this message]
2014-05-13 21:38 ` David Miller
2014-05-14 7:36 ` Heiko Carstens
Reply instructions:
You may reply publicly to this message via plain-text email
using any one of the following methods:
* Save the following mbox file, import it into your mail client,
and reply-to-all from there: mbox
Avoid top-posting and favor interleaved quoting:
https://en.wikipedia.org/wiki/Posting_style#Interleaved_style
* Reply using the --to, --cc, and --in-reply-to
switches of git-send-email(1):
git send-email \
--in-reply-to=53728E97.6030400@zytor.com \
--to=hpa@zytor.com \
--cc=ast@plumgrid.com \
--cc=davem@davemloft.net \
--cc=dborkman@redhat.com \
--cc=edumazet@google.com \
--cc=eric.dumazet@gmail.com \
--cc=heiko.carstens@de.ibm.com \
--cc=netdev@vger.kernel.org \
/path/to/YOUR_REPLY
https://kernel.org/pub/software/scm/git/docs/git-send-email.html
* If your mail client supports setting the In-Reply-To header
via mailto: links, try the mailto: link
Be sure your reply has a Subject: header at the top and a blank line
before the message body.
This is an external index of several public inboxes,
see mirroring instructions on how to clone and mirror
all data and code used by this external index.