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Wed, 23 Oct 2024 00:02:59 -0700 (PDT) MIME-Version: 1.0 References: <20241018151112.3533820-1-arnd@kernel.org> In-Reply-To: From: Marco Elver Date: Wed, 23 Oct 2024 09:02:23 +0200 Message-ID: Subject: Re: [PATCH] mm: export copy_to_kernel_nofault To: Christoph Hellwig Cc: Arnd Bergmann , Andrew Morton , Sabyrzhan Tasbolatov , Andrey Konovalov , Arnd Bergmann , linux-mm@kvack.org, linux-kernel@vger.kernel.org Content-Type: text/plain; charset="UTF-8" X-Rspamd-Queue-Id: 42841180012 X-Stat-Signature: 3yy99t3x5n58efdorkrpquz5gbddqbhg X-Rspamd-Server: rspam09 X-Rspam-User: X-HE-Tag: 1729666978-493977 X-HE-Meta: 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 fSCIAwxt GJ3NhjwBf7iVSzhmIpDLMOESGN6b2XHLgrut1+KZYCXgMmsukPnt7PYJmpX12OkctB2I4JzirWdYzHWl6C5y7xmcHyDkGXIbX9RALpy8143VhAo1mZJhd/+Jv+5RegwlG2SNNLkxCgNgBoAwK389NPv16WtVd5P2NFbo3cX8ZapSXZ4o7sXM74ZxyxOGDXpI0KYepRzQhVv5faGM9dIIi8EgrB3TAWNZtTDqW5uLBcOb+oph6kiAX50CSIEOyaQ1Pcl/X74w5dxf7zxHW1DY8b9BOrh+ddwAXwaQsCaIrXAkLbuc= X-Bogosity: Ham, tests=bogofilter, spamicity=0.000001, version=1.2.4 Sender: owner-linux-mm@kvack.org Precedence: bulk X-Loop: owner-majordomo@kvack.org List-ID: List-Subscribe: List-Unsubscribe: On Wed, 23 Oct 2024 at 08:59, Christoph Hellwig wrote: > > On Wed, Oct 23, 2024 at 08:57:02AM +0200, Marco Elver wrote: > > On Wed, 23 Oct 2024 at 08:53, Christoph Hellwig wrote: > > > > > > On Fri, Oct 18, 2024 at 03:11:09PM +0000, Arnd Bergmann wrote: > > > > From: Arnd Bergmann > > > > > > > > This symbol is now used on the kasan test module, so it needs to be > > > > exported. > > > > > > > > ERROR: modpost: "copy_to_kernel_nofault" [mm/kasan/kasan_test.ko] undefined! > > > > > > Meh, it would be great not to export internal helpers just because > > > someone wants to test them. Please just mark that test built-in only > > > instead. > > > > We have EXPORT_SYMBOL_IF_KUNIT. See include/kunit/visibility.h - > > that's more appropriate, and also adjust kasan_test.c to do > > MODULE_IMPORT_NS(EXPORTED_FOR_KUNIT_TESTING). > > Thats a little better, but at least in this case I still think it is > a very bad idea. copy_to_kernel_nofault is a perfect vector for > exploit code to probe writing to kernel address without causing faults > so it really should never ever be exported. Another alternative is to just #ifndef MODULE the offending test case, so it's only available if built-in. No need to just make the whole test built-in only. I know there are users of this particular test that rely on it being a module.