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Date: Mon, 3 Jan 2022 16:40:23 +0100 From: Alexander Lobakin <alexandr.lobakin@...el.com> To: Borislav Petkov <bp@...en8.de> Cc: Alexander Lobakin <alexandr.lobakin@...el.com>, linux-hardening@...r.kernel.org, x86@...nel.org, Jesse Brandeburg <jesse.brandeburg@...el.com>, Kristen Carlson Accardi <kristen@...ux.intel.com>, Kees Cook <keescook@...omium.org>, Miklos Szeredi <miklos@...redi.hu>, Ard Biesheuvel <ardb@...nel.org>, Tony Luck <tony.luck@...el.com>, Bruce Schlobohm <bruce.schlobohm@...el.com>, Jessica Yu <jeyu@...nel.org>, kernel test robot <lkp@...el.com>, Miroslav Benes <mbenes@...e.cz>, Evgenii Shatokhin <eshatokhin@...tuozzo.com>, Jonathan Corbet <corbet@....net>, Masahiro Yamada <masahiroy@...nel.org>, Michal Marek <michal.lkml@...kovi.net>, Nick Desaulniers <ndesaulniers@...gle.com>, Herbert Xu <herbert@...dor.apana.org.au>, "David S. Miller" <davem@...emloft.net>, Thomas Gleixner <tglx@...utronix.de>, Will Deacon <will@...nel.org>, Ingo Molnar <mingo@...hat.com>, Dave Hansen <dave.hansen@...ux.intel.com>, "H. Peter Anvin" <hpa@...or.com>, Andy Lutomirski <luto@...nel.org>, Peter Zijlstra <peterz@...radead.org>, Arnd Bergmann <arnd@...db.de>, Josh Poimboeuf <jpoimboe@...hat.com>, Nathan Chancellor <nathan@...nel.org>, Masami Hiramatsu <mhiramat@...nel.org>, Marios Pomonis <pomonis@...gle.com>, Sami Tolvanen <samitolvanen@...gle.com>, "H.J. Lu" <hjl.tools@...il.com>, Nicolas Pitre <nico@...xnic.net>, linux-kernel@...r.kernel.org, linux-kbuild@...r.kernel.org, linux-arch@...r.kernel.org, live-patching@...r.kernel.org, llvm@...ts.linux.dev Subject: Re: [PATCH v9 03/15] kallsyms: Hide layout From: Borislav Petkov <bp@...en8.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@...ux.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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