+ mm-unexport-globally-copy_to_kernel_nofault.patch added to mm-new branch

[Andrew Morton <akpm@linux-foundation.org>]

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The patch titled
     Subject: mm: unexport globally copy_to_kernel_nofault
has been added to the -mm mm-new branch.  Its filename is
     mm-unexport-globally-copy_to_kernel_nofault.patch

This patch will shortly appear at
     https://git.kernel.org/pub/scm/linux/kernel/git/akpm/25-new.git/tree/patches/mm-unexport-globally-copy_to_kernel_nofault.patch

This patch will later appear in the mm-new branch at
    git://git.kernel.org/pub/scm/linux/kernel/git/akpm/mm

Note, mm-new is a provisional staging ground for work-in-progress
patches, and acceptance into mm-new is a notification for others take
notice and to finish up reviews.  Please do not hesitate to respond to
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fixup patches in mm-new.

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------------------------------------------------------
From: Sabyrzhan Tasbolatov <snovitoll@gmail.com>
Subject: mm: unexport globally copy_to_kernel_nofault
Date: Sun, 22 Jun 2025 10:19:06 +0500

copy_to_kernel_nofault() is an internal helper which should not be visible
to loadable modules – 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.

Link: https://lkml.kernel.org/r/20250622051906.67374-1-snovitoll@gmail.com
Fixes: ca79a00bb9a8 ("kasan: migrate copy_user_test to kunit")
Signed-off-by: Sabyrzhan Tasbolatov <snovitoll@gmail.com>
Suggested-by: Christoph Hellwig <hch@infradead.org>
Suggested-by: Marco Elver <elver@google.com>
Acked-by: David Hildenbrand <david@redhat.com>
Cc: Alexander Potapenko <glider@google.com>
Cc: Andrey Konovalov <andreyknvl@gmail.com>
Cc: Andrey Ryabinin <ryabinin.a.a@gmail.com>
Cc: Arnd Bergmann <arnd@arndb.de>
Cc: Dmitriy Vyukov <dvyukov@google.com>
Cc: Vincenzo Frascino <vincenzo.frascino@arm.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
---

 mm/kasan/kasan_test_c.c |    4 ++++
 mm/maccess.c            |    1 -
 2 files changed, 4 insertions(+), 1 deletion(-)

--- a/mm/kasan/kasan_test_c.c~mm-unexport-globally-copy_to_kernel_nofault
+++ a/mm/kasan/kasan_test_c.c
@@ -1977,6 +1977,7 @@ static void rust_uaf(struct kunit *test)
 	KUNIT_EXPECT_KASAN_FAIL(test, kasan_test_rust_uaf());
 }
 
+#ifndef MODULE
 static void copy_to_kernel_nofault_oob(struct kunit *test)
 {
 	char *ptr;
@@ -2011,6 +2012,7 @@ static void copy_to_kernel_nofault_oob(s
 
 	kfree(ptr);
 }
+#endif /* !MODULE */
 
 static void copy_user_test_oob(struct kunit *test)
 {
@@ -2131,7 +2133,9 @@ static struct kunit_case kasan_kunit_tes
 	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),
 	{}
--- a/mm/maccess.c~mm-unexport-globally-copy_to_kernel_nofault
+++ a/mm/maccess.c
@@ -82,7 +82,6 @@ Efault:
 	pagefault_enable();
 	return -EFAULT;
 }
-EXPORT_SYMBOL_GPL(copy_to_kernel_nofault);
 
 long strncpy_from_kernel_nofault(char *dst, const void *unsafe_addr, long count)
 {
_

Patches currently in -mm which might be from snovitoll@gmail.com are

mm-unexport-globally-copy_to_kernel_nofault.patch