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Message-ID: <YylmwJOyDCPP11fg@der-flo.net> Date: Tue, 20 Sep 2022 09:07:44 +0200 From: Florian Lehner <dev@...-flo.net> To: Kees Cook <keescook@...omium.org> Cc: Matthew Wilcox <willy@...radead.org>, Yu Zhao <yuzhao@...gle.com>, Andrew Morton <akpm@...ux-foundation.org>, Peter Zijlstra <peterz@...radead.org>, Josh Poimboeuf <jpoimboe@...nel.org>, Dave Hansen <dave.hansen@...ux.intel.com>, x86@...nel.org, stable@...r.kernel.org, Thomas Gleixner <tglx@...utronix.de>, Ingo Molnar <mingo@...hat.com>, Borislav Petkov <bp@...en8.de>, "H. Peter Anvin" <hpa@...or.com>, Arnd Bergmann <arnd@...db.de>, Al Viro <viro@...iv.linux.org.uk>, linux-kernel@...r.kernel.org, linux-hardening@...r.kernel.org Subject: Re: [PATCH v2] x86/uaccess: Avoid check_object_size() in copy_from_user_nmi() On Mon, Sep 19, 2022 at 01:16:48PM -0700, Kees Cook wrote: > The check_object_size() helper under CONFIG_HARDENED_USERCOPY is > designed to skip any checks where the length is known at compile time as > a reasonable heuristic to avoid "likely known-good" cases. However, it can > only do this when the copy_*_user() helpers are, themselves, inline too. > > Using find_vmap_area() requires taking a spinlock. The check_object_size() > helper can call find_vmap_area() when the destination is in vmap memory. > If show_regs() is called in interrupt context, it will attempt a call to > copy_from_user_nmi(), which may call check_object_size() and then > find_vmap_area(). If something in normal context happens to be in the > middle of calling find_vmap_area() (with the spinlock held), the interrupt > handler will hang forever. > > The copy_from_user_nmi() call is actually being called with a fixed-size > length, so check_object_size() should never have been called in > the first place. Given the narrow constraints, just replace the > __copy_from_user_inatomic() call with an open-coded version that calls > only into the sanitizers and not check_object_size(), followed by a call > to raw_copy_from_user(). > > Reported-by: Yu Zhao <yuzhao@...gle.com> > Link: https://lore.kernel.org/all/CAOUHufaPshtKrTWOz7T7QFYUNVGFm0JBjvM700Nhf9qEL9b3EQ@mail.gmail.com > Reported-by: dev@...-flo.net > Suggested-by: Andrew Morton <akpm@...ux-foundation.org> > Cc: Matthew Wilcox <willy@...radead.org> > Cc: Peter Zijlstra <peterz@...radead.org> > Cc: Josh Poimboeuf <jpoimboe@...nel.org> > Cc: Dave Hansen <dave.hansen@...ux.intel.com> > Cc: x86@...nel.org > Fixes: 0aef499f3172 ("mm/usercopy: Detect vmalloc overruns") > Cc: stable@...r.kernel.org > Signed-off-by: Kees Cook <keescook@...omium.org> > --- > v2: drop the call explicitly instead of using inline to do it > v1: https://lore.kernel.org/lkml/20220916135953.1320601-1-keescook@chromium.org > --- > arch/x86/lib/usercopy.c | 3 ++- > 1 file changed, 2 insertions(+), 1 deletion(-) > > diff --git a/arch/x86/lib/usercopy.c b/arch/x86/lib/usercopy.c > index ad0139d25401..d2aff9b176cf 100644 > --- a/arch/x86/lib/usercopy.c > +++ b/arch/x86/lib/usercopy.c > @@ -44,7 +44,8 @@ copy_from_user_nmi(void *to, const void __user *from, unsigned long n) > * called from other contexts. > */ > pagefault_disable(); > - ret = __copy_from_user_inatomic(to, from, n); > + instrument_copy_from_user(to, from, n); > + ret = raw_copy_from_user(to, from, n); > pagefault_enable(); > > return ret; > -- > 2.34.1 > Thanks! Tested-by: Florian Lehner <dev@...-flo.net>
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