linux-kernel - Re: [PATCH 4/4] objtool: add UACCESS exceptions for __tsan_volatile

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Date:   Wed, 8 Feb 2023 17:59:05 +0100
From:   Marco Elver <elver@...gle.com>
To:     Arnd Bergmann <arnd@...nel.org>
Cc:     Josh Poimboeuf <jpoimboe@...nel.org>,
        Peter Zijlstra <peterz@...radead.org>,
        Borislav Petkov <bp@...e.de>, Will Deacon <will@...nel.org>,
        Thomas Gleixner <tglx@...utronix.de>,
        kasan-dev@...glegroups.com, Dmitry Vyukov <dvyukov@...gle.com>,
        Alexander Potapenko <glider@...gle.com>,
        Andrey Ryabinin <ryabinin.a.a@...il.com>,
        Vincenzo Frascino <vincenzo.frascino@....com>,
        Andrey Konovalov <andreyknvl@...il.com>,
        Arnd Bergmann <arnd@...db.de>, Miroslav Benes <mbenes@...e.cz>,
        "Naveen N. Rao" <naveen.n.rao@...ux.vnet.ibm.com>,
        Sathvika Vasireddy <sv@...ux.ibm.com>,
        linux-kernel@...r.kernel.org
Subject: Re: [PATCH 4/4] objtool: add UACCESS exceptions for __tsan_volatile_read/write

On Wed, 8 Feb 2023 at 17:40, Arnd Bergmann <arnd@...nel.org> wrote:
>
> From: Arnd Bergmann <arnd@...db.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@...db.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
>
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