MIME-Version: 1.0
References: <20230208164011.2287122-1-arnd@kernel.org> <20230208164011.2287122-4-arnd@kernel.org>
In-Reply-To: <20230208164011.2287122-4-arnd@kernel.org>
From:   Marco Elver <elver@google.com>
Date:   Wed, 8 Feb 2023 17:59:05 +0100
Message-ID: <CANpmjNN1nmjavBhj=xMMqAD1VScPySkdZbm2sTpWnKN1ZvmJcQ@mail.gmail.com>
Subject: Re: [PATCH 4/4] objtool: add UACCESS exceptions for __tsan_volatile_read/write
To:     Arnd Bergmann <arnd@kernel.org>
Cc:     Josh Poimboeuf <jpoimboe@kernel.org>,
        Peter Zijlstra <peterz@infradead.org>,
        Borislav Petkov <bp@suse.de>, Will Deacon <will@kernel.org>,
        Thomas Gleixner <tglx@linutronix.de>,
        kasan-dev@googlegroups.com, Dmitry Vyukov <dvyukov@google.com>,
        Alexander Potapenko <glider@google.com>,
        Andrey Ryabinin <ryabinin.a.a@gmail.com>,
        Vincenzo Frascino <vincenzo.frascino@arm.com>,
        Andrey Konovalov <andreyknvl@gmail.com>,
        Arnd Bergmann <arnd@arndb.de>, Miroslav Benes <mbenes@suse.cz>,
        "Naveen N. Rao" <naveen.n.rao@linux.vnet.ibm.com>,
        Sathvika Vasireddy <sv@linux.ibm.com>,
        linux-kernel@vger.kernel.org
Content-Type: text/plain; charset="UTF-8"
Precedence: bulk

On Wed, 8 Feb 2023 at 17:40, Arnd Bergmann <arnd@kernel.org> wrote:
>
> From: Arnd Bergmann <arnd@arndb.de>
>
> A lot of the tsan helpers are already excempt from the UACCESS warnings,
> but some more functions were added that need the same thing:
>
> kernel/kcsan/core.o: warning: objtool: __tsan_volatile_read16+0x0: call to __tsan_unaligned_read16() with UACCESS enabled
> kernel/kcsan/core.o: warning: objtool: __tsan_volatile_write16+0x0: call to __tsan_unaligned_write16() with UACCESS enabled
> vmlinux.o: warning: objtool: __tsan_unaligned_volatile_read16+0x4: call to __tsan_unaligned_read16() with UACCESS enabled
> vmlinux.o: warning: objtool: __tsan_unaligned_volatile_write16+0x4: call to __tsan_unaligned_write16() with UACCESS enabled

That's odd - this has never been needed, because all __tsan_unaligned
are aliases for the non-unaligned functions. And all those are in the
uaccess_safe_builtin list already.

So if suddenly the alias name becomes the symbol that objtool sees, we
might need to add all the other functions as well.

Is this a special build with a new compiler?

> Fixes: 75d75b7a4d54 ("kcsan: Support distinguishing volatile accesses")
> Signed-off-by: Arnd Bergmann <arnd@arndb.de>
> ---
>  tools/objtool/check.c | 2 ++
>  1 file changed, 2 insertions(+)
>
> diff --git a/tools/objtool/check.c b/tools/objtool/check.c
> index e8fb3bf7a2e3..d89ef6957021 100644
> --- a/tools/objtool/check.c
> +++ b/tools/objtool/check.c
> @@ -1200,6 +1200,8 @@ static const char *uaccess_safe_builtin[] = {
>         "__tsan_atomic64_compare_exchange_val",
>         "__tsan_atomic_thread_fence",
>         "__tsan_atomic_signal_fence",
> +       "__tsan_unaligned_read16",
> +       "__tsan_unaligned_write16",
>         /* KCOV */
>         "write_comp_data",
>         "check_kcov_mode",
> --
> 2.39.1
>
> --
> You received this message because you are subscribed to the Google Groups "kasan-dev" group.
> To unsubscribe from this group and stop receiving emails from it, send an email to kasan-dev+unsubscribe@googlegroups.com.
> To view this discussion on the web visit https://groups.google.com/d/msgid/kasan-dev/20230208164011.2287122-4-arnd%40kernel.org.