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[84.3.50.134]) by smtp.gmail.com with ESMTPSA id v24sm7138834eds.71.2020.07.27.04.21.45 (version=TLS1_3 cipher=TLS_AES_256_GCM_SHA384 bits=256/256); Mon, 27 Jul 2020 04:21:46 -0700 (PDT) Date: Mon, 27 Jul 2020 13:21:44 +0200 From: Ingo Molnar To: peterz@infradead.org Cc: Josh Poimboeuf , Thomas Gleixner , x86@kernel.org, linux-kernel@vger.kernel.org, mbenes@suse.cz Subject: Re: [PATCH] objtool,x86: Verify poke_int3_handler() is self contained Message-ID: <20200727112144.GA55660@gmail.com> References: <20200727104050.GH119549@hirez.programming.kicks-ass.net> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20200727104050.GH119549@hirez.programming.kicks-ass.net> Sender: linux-kernel-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org * peterz@infradead.org wrote: > > Abuse the SMAP rules to ensure poke_int3_handler() doesn't call out to > anything. > > Signed-off-by: Peter Zijlstra (Intel) > --- > tools/objtool/check.c | 8 ++++++++ > 1 file changed, 8 insertions(+) > > --- a/tools/objtool/check.c > +++ b/tools/objtool/check.c > @@ -551,6 +551,14 @@ static const char *uaccess_safe_builtin[ > "__memcpy_mcsafe", > "mcsafe_handle_tail", > "ftrace_likely_update", /* CONFIG_TRACE_BRANCH_PROFILING */ > + /* > + * Abuse alert! > + * > + * poke_int3_handler() is not in fact related to uaccess at all, we > + * abuse the uaccess rules to ensure poke_int3_handler() is self > + * contained and doesn't CALL out to other code. > + */ > + "poke_int3_handler", So ->uaccess_safe makes sure that we don't CALL into non-uaccess-safe functions, but it still allows CALLs into *other* uaccess-safe functions, right? So unless I missed something in the logic, the comment should say something like "doesn't CALL out to other non-uaccess safe code" or so? Which is, arguably, like 99% of all functions - but still, a whole bunch are allowed, such as low level instrumentation and other utility functions. Thanks, Ingo