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[3.122.242.201]) by smtp.gmail.com with ESMTPSA id ffacd0b85a97d-3a6d297ccbcsm6775771f8f.91.2025.06.22.07.11.51 (version=TLS1_3 cipher=TLS_AES_256_GCM_SHA384 bits=256/256); Sun, 22 Jun 2025 07:11:53 -0700 (PDT) From: Sabyrzhan Tasbolatov To: andreyknvl@gmail.com Cc: akpm@linux-foundation.org, arnd@arndb.de, david@redhat.com, dvyukov@google.com, elver@google.com, glider@google.com, hch@infradead.org, kasan-dev@googlegroups.com, linux-kernel@vger.kernel.org, linux-mm@kvack.org, ryabinin.a.a@gmail.com, snovitoll@gmail.com, vincenzo.frascino@arm.com Subject: [PATCH v2] mm: unexport globally copy_to_kernel_nofault Date: Sun, 22 Jun 2025 19:11:42 +0500 Message-Id: <20250622141142.79332-1-snovitoll@gmail.com> X-Mailer: git-send-email 2.34.1 In-Reply-To: References: Precedence: bulk X-Mailing-List: linux-kernel@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 Content-Type: text/plain; charset="utf-8" Content-Transfer-Encoding: quoted-printable `copy_to_kernel_nofault()` is an internal helper which should not be visible to loadable modules =E2=80=93 exporting it would give exploit code a cheap oracle to probe kernel addresses. Instead, keep the helper un-exported and compile the kunit case that exercises it only when `mm/kasan/kasan_test.o` is linked into vmlinux. Fixes: ca79a00bb9a8 ("kasan: migrate copy_user_test to kunit") Suggested-by: Christoph Hellwig Suggested-by: Marco Elver Reviewed-by: Andrey Konovalov Signed-off-by: Sabyrzhan Tasbolatov Acked-by: Arnd Bergmann Acked-by: David Hildenbrand --- Changes v2: - add a brief comment to `#ifndef MODULE` --- mm/kasan/kasan_test_c.c | 8 ++++++++ mm/maccess.c | 1 - 2 files changed, 8 insertions(+), 1 deletion(-) diff --git a/mm/kasan/kasan_test_c.c b/mm/kasan/kasan_test_c.c index 5f922dd38ffa..2aa12dfa427a 100644 --- a/mm/kasan/kasan_test_c.c +++ b/mm/kasan/kasan_test_c.c @@ -1977,6 +1977,11 @@ static void rust_uaf(struct kunit *test) KUNIT_EXPECT_KASAN_FAIL(test, kasan_test_rust_uaf()); } =20 +/* + * copy_to_kernel_nofault() is an internal helper available when + * kasan_test is built-in, so it must not be visible to loadable modules. + */ +#ifndef MODULE static void copy_to_kernel_nofault_oob(struct kunit *test) { char *ptr; @@ -2011,6 +2016,7 @@ static void copy_to_kernel_nofault_oob(struct kunit *= test) =20 kfree(ptr); } +#endif /* !MODULE */ =20 static void copy_user_test_oob(struct kunit *test) { @@ -2131,7 +2137,9 @@ static struct kunit_case kasan_kunit_test_cases[] =3D= { KUNIT_CASE(match_all_not_assigned), KUNIT_CASE(match_all_ptr_tag), KUNIT_CASE(match_all_mem_tag), +#ifndef MODULE KUNIT_CASE(copy_to_kernel_nofault_oob), +#endif KUNIT_CASE(rust_uaf), KUNIT_CASE(copy_user_test_oob), {} diff --git a/mm/maccess.c b/mm/maccess.c index 831b4dd7296c..486559d68858 100644 --- a/mm/maccess.c +++ b/mm/maccess.c @@ -82,7 +82,6 @@ long copy_to_kernel_nofault(void *dst, const void *src, s= ize_t size) pagefault_enable(); return -EFAULT; } -EXPORT_SYMBOL_GPL(copy_to_kernel_nofault); =20 long strncpy_from_kernel_nofault(char *dst, const void *unsafe_addr, long = count) { --=20 2.34.1