Messages in this thread | | | From | Alexander Lobakin <> | Subject | Re: [PATCH v9 03/15] kallsyms: Hide layout | Date | Mon, 3 Jan 2022 16:40:23 +0100 |
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From: Borislav Petkov <bp@alien8.de> Date: Thu, 30 Dec 2021 23:36:00 +0100
> On Thu, Dec 23, 2021 at 01:21:57AM +0100, Alexander Lobakin wrote: > > Subject: Re: [PATCH v9 03/15] kallsyms: Hide layout > > That title is kinda laconic...
"kallsyms: randomize /proc/kallsyms output order"?
> > > From: Kristen Carlson Accardi <kristen@linux.intel.com> > > > > This patch makes /proc/kallsyms display in a random order, rather > > Avoid having "This patch" or "This commit" in the commit message. It is > tautologically useless. > > Also, do > > $ git grep 'This patch' Documentation/process > > for more details.
Goes straight from the original series. Worth changing anyways.
> > > than sorted by address in order to hide the newly randomized address > > layout. > > Sorted by address? > > My /proc/kallsyms says > > $ awk '{ print $1 }' /proc/kallsyms | uniq -c > 119086 0000000000000000 > > so all the addresses are 0. Aha, and when I list them as root, only then > I see non-null addresses. > > So why do we that patch at all?
It displays zeros for non-roots, but the symbols are still sorted by their addresses. As a result, if you leak one address, you could determine some others. This is especially critical with FG-KASLR as its text layout is random each time and sorted /proc/kallsyms would make the entire feature useless.
> > > alobakin: > > Don't depend FG-KASLR and always do that for unpriviledged accesses > > Unknown word [unpriviledged] in commit message, suggestions: > ['unprivileged', 'underprivileged', 'privileged']
I either have some problems with checkpatch + codespell, or they missed all that typos you're noticing. Thanks, and apologies =\
> > > as suggested by several folks. > > Also, introduce and use a shuffle_array() macro which shuffles an > > array using Fisher-Yates. > > Fisher-Yates what? > > /me goes and looks at the wikipedia article. > > Aha, a Fisher-Yates shuffle algoithm. > > Don't be afraid to explain more in your commit messages and make them > more reader-friendly.
Sure. This patch initially was at the tail of the set, after the commits where this algo is mentioned several times in a more detailed manner, but I moved it to the head then as the requests for doing this unconditionally converted it to a pre-requisite.
> > > We'll make use of it several more times > > later on. > > Not important for this commit. > > ... > > -- > Regards/Gruss, > Boris. > > https://people.kernel.org/tglx/notes-about-netiquette
Thanks! Al
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