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Here is the patch set that implements hashing of printk specifier
%p. First we have two clean up patches then we do the hashing. Hashing
is done via the SipHash algorithm. The next patch adds printk specifier
%px for printing pointers when we _really_ want to see the address i.e
%px is functionally equivalent to %lx. Final patch in the set fixes
KASAN since we break it by hashing %p.
For the record here is the justification for the series.
Currently there exist approximately 14 000 places in the Kernel where
addresses are being printed using an unadorned %p. This potentially
leaks sensitive information about the Kernel layout in memory. Many of
these calls are stale, instead of fixing every call we hash the address
by default before printing. We then add %px to provide a way to print
the actual address. Although this is achievable using %lx, using %px
will assist us if we ever want to change pointer printing behaviour. %px
is more uniquely grep'able (there are already >50 000 uses of %lx).
The added advantage of hashing %p is that security is now opt-out, if
you _really_ want the address you have to work a little harder and use
%px.
This will of course break some users, forcing code printing needed
addresses to be updated.
Signed-off-by: Tobin C. Harding <me@tobin.cc>
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Merge tag 'printk-hash-pointer-4.15-rc2' of git://github.com/tcharding/linux
Pull printk pointer hashing update from Tobin Harding:
"Here is the patch set that implements hashing of printk specifier %p.
First we have two clean up patches then we do the hashing. Hashing is
done via the SipHash algorithm. The next patch adds printk specifier
%px for printing pointers when we _really_ want to see the address i.e
%px is functionally equivalent to %lx. Final patch in the set fixes
KASAN since we break it by hashing %p.
For the record here is the justification for the series:
Currently there exist approximately 14 000 places in the Kernel
where addresses are being printed using an unadorned %p. This
potentially leaks sensitive information about the Kernel layout in
memory. Many of these calls are stale, instead of fixing every call
we hash the address by default before printing. We then add %px to
provide a way to print the actual address. Although this is
achievable using %lx, using %px will assist us if we ever want to
change pointer printing behaviour. %px is more uniquely grep'able
(there are already >50 000 uses of %lx).
The added advantage of hashing %p is that security is now opt-out,
if you _really_ want the address you have to work a little harder
and use %px.
This will of course break some users, forcing code printing needed
addresses to be updated"
[ I do expect this to be an annoyance, and a number of %px users to be
added for debuggability. But nobody is willing to audit existing %p
users for information leaks, and a number of places really only use
the pointer as an object identifier rather than really 'I need the
address'.
IOW - sorry for the inconvenience, but it's the least inconvenient of
the options. - Linus ]
* tag 'printk-hash-pointer-4.15-rc2' of git://github.com/tcharding/linux:
kasan: use %px to print addresses instead of %p
vsprintf: add printk specifier %px
printk: hash addresses printed with %p
vsprintf: refactor %pK code out of pointer()
docs: correct documentation for %pK
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Linux kernel ============ This file was moved to Documentation/admin-guide/README.rst Please notice that there are several guides for kernel developers and users. These guides can be rendered in a number of formats, like HTML and PDF. In order to build the documentation, use ``make htmldocs`` or ``make pdfdocs``. There are various text files in the Documentation/ subdirectory, several of them using the Restructured Text markup notation. See Documentation/00-INDEX for a list of what is contained in each file. Please read the Documentation/process/changes.rst file, as it contains the requirements for building and running the kernel, and information about the problems which may result by upgrading your kernel.