From: Solar Designer <solar@openwall.com>
To: kernel-hardening@lists.openwall.com
Subject: Re: [kernel-hardening] [RFC] x86, mm: start mmap allocation for libs from low addresses
Date: Wed, 7 Sep 2011 14:16:08 +0400 [thread overview]
Message-ID: <20110907101608.GA17974@openwall.com> (raw)
In-Reply-To: <20110907095508.GA16114@albatros>
On Wed, Sep 07, 2011 at 01:55:08PM +0400, Vasiliy Kulikov wrote:
> OK, fully agree. But why 100 KB? Probably 0x10000 (64 KB)? It looks
> nicer and not so magic.
Well, on Owl we have mmap_min_addr at 96 KB, which is sufficient e.g. in
case we have a struct field offset not larger than 32 KB and the field
itself is an array indexed by a 16-bit value. Or if the field offset is
not larger than 64 KB and the index is a signed 16-bit value.
100 KB is a very cheap enhancement of the above, also allowing for two
levels of indirection (up to one 16-bit signed and one 16-bit unsigned)
relative to a fixed offset that fits in 4 KB.
Maybe we should move from 96 KB to 100 KB for Owl's mmap_min_addr
default. Or maybe we should use 132 KB (4+64+64).
Oh, this assumes arrays of char, or our 16-bit variable being byte
offset rather than index. 132 KB would also support arrays of 16-bit
words, and even 16-bit signed indexes into arrays of 32-bit words.
OK, maybe I am imagining these possibilities, but to me these values
feel a little bit more reasonable than a mere 64 KB, which might be
just insufficient e.g. if we have a 16-bit unsigned byte offset variable
and the array itself is a struct field. Even 68 KB would be a lot more
likely to help then.
Alexander
next prev parent reply other threads:[~2011-09-07 10:16 UTC|newest]
Thread overview: 29+ messages / expand[flat|nested] mbox.gz Atom feed top
2011-08-12 10:29 [kernel-hardening] [RFC] x86, mm: start mmap allocation for libs from low addresses Vasiliy Kulikov
2011-08-12 10:58 ` Solar Designer
2011-08-12 11:05 ` Vasiliy Kulikov
2011-08-25 17:19 ` Vasiliy Kulikov
2011-08-25 17:39 ` Solar Designer
2011-09-02 18:29 ` Solar Designer
2011-09-03 11:18 ` Vasiliy Kulikov
2011-09-03 23:57 ` Solar Designer
2011-09-05 12:46 ` Vasiliy Kulikov
2011-09-06 5:05 ` Solar Designer
2011-09-07 9:09 ` Vasiliy Kulikov
2011-09-07 9:30 ` Solar Designer
2011-09-07 9:34 ` Vasiliy Kulikov
2011-09-07 9:43 ` Solar Designer
2011-09-07 9:55 ` Vasiliy Kulikov
2011-09-07 10:16 ` Solar Designer [this message]
2011-09-07 11:01 ` Vasiliy Kulikov
2011-09-02 23:34 ` Solar Designer
2011-09-03 12:12 ` Vasiliy Kulikov
2011-09-03 23:40 ` Solar Designer
2011-09-04 7:21 ` Vasiliy Kulikov
2011-08-12 23:19 ` [kernel-hardening] " H. Peter Anvin
2011-08-13 6:26 ` Vasiliy Kulikov
2011-08-16 9:05 ` Vasiliy Kulikov
2011-08-22 10:17 ` Vasiliy Kulikov
2011-08-22 17:24 ` H. Peter Anvin
2011-08-22 20:14 ` Vasiliy Kulikov
2011-08-22 20:17 ` H. Peter Anvin
2011-08-23 6:41 ` Vasiliy Kulikov
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