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Date:   Wed, 30 Mar 2022 10:58:26 +0200
From:   Peter Zijlstra <peterz@infradead.org>
To:     Alexander Potapenko <glider@google.com>
Cc:     Alexander Viro <viro@zeniv.linux.org.uk>,
        Andrew Morton <akpm@linux-foundation.org>,
        Andrey Konovalov <andreyknvl@google.com>,
        Andy Lutomirski <luto@kernel.org>,
        Arnd Bergmann <arnd@arndb.de>, Borislav Petkov <bp@alien8.de>,
        Christoph Hellwig <hch@lst.de>,
        Christoph Lameter <cl@linux.com>,
        David Rientjes <rientjes@google.com>,
        Dmitry Vyukov <dvyukov@google.com>,
        Eric Dumazet <edumazet@google.com>,
        Greg Kroah-Hartman <gregkh@linuxfoundation.org>,
        Herbert Xu <herbert@gondor.apana.org.au>,
        Ilya Leoshkevich <iii@linux.ibm.com>,
        Ingo Molnar <mingo@redhat.com>, Jens Axboe <axboe@kernel.dk>,
        Joonsoo Kim <iamjoonsoo.kim@lge.com>,
        Kees Cook <keescook@chromium.org>,
        Marco Elver <elver@google.com>,
        Mark Rutland <mark.rutland@arm.com>,
        Matthew Wilcox <willy@infradead.org>,
        "Michael S. Tsirkin" <mst@redhat.com>,
        Pekka Enberg <penberg@kernel.org>,
        Petr Mladek <pmladek@suse.com>,
        Steven Rostedt <rostedt@goodmis.org>,
        Thomas Gleixner <tglx@linutronix.de>,
        Vasily Gorbik <gor@linux.ibm.com>,
        Vegard Nossum <vegard.nossum@oracle.com>,
        Vlastimil Babka <vbabka@suse.cz>, linux-mm@kvack.org,
        linux-arch@vger.kernel.org, linux-kernel@vger.kernel.org,
        ryabinin.a.a@gmail.com
Subject: Re: [PATCH v2 13/48] kmsan: add KMSAN runtime core
Message-ID: <20220330085826.GI8939@worktop.programming.kicks-ass.net>
References: <20220329124017.737571-1-glider@google.com>
 <20220329124017.737571-14-glider@google.com>
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On Tue, Mar 29, 2022 at 02:39:42PM +0200, Alexander Potapenko wrote:
> +/* Handle llvm.memmove intrinsic. */
> +void *__msan_memmove(void *dst, const void *src, uintptr_t n)
> +{
> +	void *result;
> +
> +	result = __memmove(dst, src, n);
> +	if (!n)
> +		/* Some people call memmove() with zero length. */
> +		return result;
> +	if (!kmsan_enabled || kmsan_in_runtime())
> +		return result;
> +
> +	kmsan_internal_memmove_metadata(dst, (void *)src, n);
> +
> +	return result;
> +}
> +EXPORT_SYMBOL(__msan_memmove);
> +
> +/* Handle llvm.memcpy intrinsic. */
> +void *__msan_memcpy(void *dst, const void *src, uintptr_t n)
> +{
> +	void *result;
> +
> +	result = __memcpy(dst, src, n);
> +	if (!n)
> +		/* Some people call memcpy() with zero length. */
> +		return result;
> +
> +	if (!kmsan_enabled || kmsan_in_runtime())
> +		return result;
> +
> +	/* Using memmove instead of memcpy doesn't affect correctness. */
> +	kmsan_internal_memmove_metadata(dst, (void *)src, n);
> +
> +	return result;
> +}
> +EXPORT_SYMBOL(__msan_memcpy);
> +
> +/* Handle llvm.memset intrinsic. */
> +void *__msan_memset(void *dst, int c, uintptr_t n)
> +{
> +	void *result;
> +
> +	result = __memset(dst, c, n);
> +	if (!kmsan_enabled || kmsan_in_runtime())
> +		return result;
> +
> +	kmsan_enter_runtime();
> +	/*
> +	 * Clang doesn't pass parameter metadata here, so it is impossible to
> +	 * use shadow of @c to set up the shadow for @dst.
> +	 */
> +	kmsan_internal_unpoison_memory(dst, n, /*checked*/ false);
> +	kmsan_leave_runtime();
> +
> +	return result;
> +}
> +EXPORT_SYMBOL(__msan_memset);

This, we need this same for KASAN. KASAN must be changed to have the
mem*() intrinsics emit __asan_mem*(), such that we can have
uninstrumented base functions.

Currently we seem to have the problem that when a noinstr function trips
one of those instrinsics it'll emit a call to an instrumented function,
which is a complete no-no.

Also see:

  https://lore.kernel.org/all/YjxTt3pFIcV3lt8I@zn.tnic/T/#m2049a14be400d4ae2b54a1f7da3ede28b7fd7564

Given the helpful feedback there, Mark and me are going to unilaterally
break Kasan by deleting the existing wrappers.