Messages in this thread | | | From | Arvind Sankar <> | Date | Tue, 8 Sep 2020 14:40:03 -0400 | Subject | Re: [RFC PATCH 1/2] lib/string: Disable instrumentation |
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On Tue, Sep 08, 2020 at 10:21:32AM -0700, Kees Cook wrote: > On Tue, Sep 08, 2020 at 11:39:11AM +0200, Marco Elver wrote: > > On Sun, 6 Sep 2020 at 00:23, Arvind Sankar <nivedita@alum.mit.edu> wrote: > > > > > > String functions can be useful in early boot, but using instrumented > > > versions can be problematic: eg on x86, some of the early boot code is > > > executing out of an identity mapping rather than the kernel virtual > > > addresses. Accessing any global variables at this point will lead to a > > > crash. > > > > > > > Ouch. > > > > We have found manifestations of bugs in lib/string.c functions, e.g.: > > https://groups.google.com/forum/#!msg/syzkaller-bugs/atbKWcFqE9s/x7AtoVoBAgAJ > > https://groups.google.com/forum/#!msg/syzkaller-bugs/iGBUm-FDhkM/chl05uEgBAAJ > > > > Is there any way this can be avoided? > > Agreed: I would like to keep this instrumentation; it's a common place > to find bugs, security issues, etc. > > -- > Kees Cook
Ok, understood. I'll revise to open-code the strscpy instead.
Is instrumentation supported on x86-32? load_ucode_bsp() on 32-bit is called before paging is enabled, and load_ucode_bsp() itself, along with eg lib/earlycpio and lib/string that it uses, don't have anything to disable instrumentation. kcov, kasan, kcsan are unsupported already on 32-bit, but the others like gcov and PROFILE_ALL_BRANCHES look like they would just cause a crash if microcode loading is enabled.
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