From: David Miller <davem@davemloft.net>
To: hpa@zytor.com
Cc: ast@plumgrid.com, eric.dumazet@gmail.com, edumazet@google.com,
dborkman@redhat.com, heiko.carstens@de.ibm.com,
netdev@vger.kernel.org
Subject: Re: [PATCH net] net: filter: x86: fix JIT address randomization
Date: Tue, 13 May 2014 17:38:28 -0400 (EDT) [thread overview]
Message-ID: <20140513.173828.1128380962164004400.davem@davemloft.net> (raw)
In-Reply-To: <53728E97.6030400@zytor.com>
From: "H. Peter Anvin" <hpa@zytor.com>
Date: Tue, 13 May 2014 14:28:55 -0700
> 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.
Agreed.
>> 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.
Also agreed.
next prev parent reply other threads:[~2014-05-13 21:38 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
2014-05-13 21:38 ` David Miller [this message]
2014-05-14 7:36 ` Heiko Carstens
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