linux-kernel - Re: [PATCH 23/25] objtool: Add UACCESS validation

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Message-ID: <20190507115200.GT2606@hirez.programming.kicks-ass.net>
Date:   Tue, 7 May 2019 13:52:00 +0200
From:   Peter Zijlstra <peterz@...radead.org>
To:     torvalds@...ux-foundation.org, tglx@...utronix.de, hpa@...or.com,
        julien.thierry@....com, will.deacon@....com, luto@...capital.net,
        mingo@...nel.org, catalin.marinas@....com, james.morse@....com,
        valentin.schneider@....com, brgerst@...il.com, jpoimboe@...hat.com,
        luto@...nel.org, bp@...en8.de, dvlasenk@...hat.com
Cc:     linux-kernel@...r.kernel.org, dvyukov@...gle.com,
        rostedt@...dmis.org
Subject: Re: [PATCH 23/25] objtool: Add UACCESS validation

On Mon, Mar 18, 2019 at 04:39:03PM +0100, Peter Zijlstra wrote:
> +static const char *uaccess_safe_builtin[] = {
> +	/* KASAN */
> +	"kasan_report",
> +	"check_memory_region",
> +	/* KASAN out-of-line */
> +	"__asan_loadN_noabort",
> +	"__asan_load1_noabort",
> +	"__asan_load2_noabort",
> +	"__asan_load4_noabort",
> +	"__asan_load8_noabort",
> +	"__asan_load16_noabort",
> +	"__asan_storeN_noabort",
> +	"__asan_store1_noabort",
> +	"__asan_store2_noabort",
> +	"__asan_store4_noabort",
> +	"__asan_store8_noabort",
> +	"__asan_store16_noabort",
> +	/* KASAN in-line */
> +	"__asan_report_load_n_noabort",
> +	"__asan_report_load1_noabort",
> +	"__asan_report_load2_noabort",
> +	"__asan_report_load4_noabort",
> +	"__asan_report_load8_noabort",
> +	"__asan_report_load16_noabort",
> +	"__asan_report_store_n_noabort",
> +	"__asan_report_store1_noabort",
> +	"__asan_report_store2_noabort",
> +	"__asan_report_store4_noabort",
> +	"__asan_report_store8_noabort",
> +	"__asan_report_store16_noabort",

So I was building the kernel with GCC-4.9 (for another issue) and that
got me:

arch/x86/kernel/signal.o: warning: objtool: restore_sigcontext()+0x69: call to __asan_store8() with UACCESS enabled
arch/x86/kernel/signal.o: warning: objtool: setup_sigcontext()+0x3d: call to __asan_load8() with UACCESS enabled
arch/x86/kernel/signal.o: warning: objtool: __setup_rt_frame()+0x308: call to __asan_load8() with UACCESS enabled
lib/strncpy_from_user.o: warning: objtool: strncpy_from_user()+0x33d: call to __asan_store1() with UACCESS enabled
lib/ubsan.o: warning: objtool: __ubsan_handle_type_mismatch_v1()+0x19: call to __asan_load8() with UACCESS enabled
lib/ubsan.o: warning: objtool: __ubsan_handle_type_mismatch()+0x19: call to __asan_load8() with UACCESS enabled

Can any of the KASAN folks enlighten me on this? Should I also whitelist
those symbols, and do I understand things correct that the difference
between * and *_noabort is absolutely nothing?