kbuild: rust: keep Rust objects out of Clang LTO with inline helpersgrafted

Under `CONFIG_LTO_CLANG` + `CONFIG_RUST_INLINE_HELPERS`, one may hit
`objtool` errors such as:

    vmlinux.o: error: objtool: _R..._3Gsp4boot+0xd6a:
    can't find jump dest instruction at .text._R..._3Gsp4boot+0x1dfd

The reason is that in such builds, the Clang invocation that compiles
the combined Rust plus helpers bitcode emits LLVM bitcode (again) --
the final code generation happens in the linker's LTO step, which the
`-mllvm` trap options passed to Clang do not reach.

This, in turn, means that unreachable traps are missing, and the
impossible paths do not merely fallthrough to the next symbol, but past
the end of their own section, since LTO builds place each function in
its own section.

Thus filter `CC_FLAGS_LTO` out of the Clang invocation, so that it always
emits machine code directly, with the traps in place.

Assisted-by: LLM
Cc: Gary Guo <gary@garyguo.net>
Cc: Boqun Feng <boqun@kernel.org>
Cc: Alice Ryhl <aliceryhl@google.com>
Cc: Matthew Maurer <mmaurer@google.com>
Cc: Josh Poimboeuf <jpoimboe@kernel.org>
Cc: Peter Zijlstra <peterz@infradead.org>
Cc: stable@vger.kernel.org
Fixes: 3a2486cc1da5 ("kbuild: rust: provide an option to inline C helpers into Rust")
Acked-by: Gary Guo <gary@garyguo.net>
Link: https://patch.msgid.link/20260816133233.197500-2-ojeda@kernel.org
Signed-off-by: Miguel Ojeda <ojeda@kernel.org>

1 files changed, 336 insertions, 0 deletions

diff --git a/lib/tests/usercopy_kunit.c b/lib/tests/usercopy_kunit.c
new file mode 100644
index 000000000..80f8abe10
--- /dev/null
+++ b/lib/tests/usercopy_kunit.c
@@ -0,0 +1,336 @@
+// SPDX-License-Identifier: GPL-2.0-only
+/*
+ * Kernel module for testing copy_to/from_user infrastructure.
+ *
+ * Copyright 2013 Google Inc. All Rights Reserved
+ *
+ * Authors:
+ *      Kees Cook       <keescook@chromium.org>
+ */
+
+#define pr_fmt(fmt) KBUILD_MODNAME ": " fmt
+
+#include <linux/mman.h>
+#include <linux/module.h>
+#include <linux/sched.h>
+#include <linux/slab.h>
+#include <linux/uaccess.h>
+#include <kunit/test.h>
+
+/*
+ * Several 32-bit architectures support 64-bit {get,put}_user() calls.
+ * As there doesn't appear to be anything that can safely determine
+ * their capability at compile-time, we just have to opt-out certain archs.
+ */
+#if BITS_PER_LONG == 64 || (!(defined(CONFIG_ARM) && !defined(MMU)) && \
+			    !defined(CONFIG_M68K) &&		\
+			    !defined(CONFIG_MICROBLAZE) &&	\
+			    !defined(CONFIG_NIOS2) &&		\
+			    !defined(CONFIG_PPC32) &&		\
+			    !defined(CONFIG_SPARC32) &&		\
+			    !defined(CONFIG_SUPERH))
+# define TEST_U64
+#endif
+
+struct usercopy_test_priv {
+	char *kmem;
+	char __user *umem;
+	size_t size;
+};
+
+static bool is_zeroed(void *from, size_t size)
+{
+	return memchr_inv(from, 0x0, size) == NULL;
+}
+
+/* Test usage of check_nonzero_user(). */
+static void usercopy_test_check_nonzero_user(struct kunit *test)
+{
+	size_t start, end, i, zero_start, zero_end;
+	struct usercopy_test_priv *priv = test->priv;
+	char __user *umem = priv->umem;
+	char *kmem = priv->kmem;
+	size_t size = priv->size;
+
+	KUNIT_ASSERT_GE_MSG(test, size, 2 * PAGE_SIZE, "buffer too small");
+
+	/*
+	 * We want to cross a page boundary to exercise the code more
+	 * effectively. We also don't want to make the size we scan too large,
+	 * otherwise the test can take a long time and cause soft lockups. So
+	 * scan a 1024 byte region across the page boundary.
+	 */
+	size = 1024;
+	start = PAGE_SIZE - (size / 2);
+
+	kmem += start;
+	umem += start;
+
+	zero_start = size / 4;
+	zero_end = size - zero_start;
+
+	/*
+	 * We conduct a series of check_nonzero_user() tests on a block of
+	 * memory with the following byte-pattern (trying every possible
+	 * [start,end] pair):
+	 *
+	 *   [ 00 ff 00 ff ... 00 00 00 00 ... ff 00 ff 00 ]
+	 *
+	 * And we verify that check_nonzero_user() acts identically to
+	 * memchr_inv().
+	 */
+
+	memset(kmem, 0x0, size);
+	for (i = 1; i < zero_start; i += 2)
+		kmem[i] = 0xff;
+	for (i = zero_end; i < size; i += 2)
+		kmem[i] = 0xff;
+
+	KUNIT_EXPECT_EQ_MSG(test, copy_to_user(umem, kmem, size), 0,
+		"legitimate copy_to_user failed");
+
+	for (start = 0; start <= size; start++) {
+		for (end = start; end <= size; end++) {
+			size_t len = end - start;
+			int retval = check_zeroed_user(umem + start, len);
+			int expected = is_zeroed(kmem + start, len);
+
+			KUNIT_ASSERT_EQ_MSG(test, retval, expected,
+				"check_nonzero_user(=%d) != memchr_inv(=%d) mismatch (start=%zu, end=%zu)",
+				retval, expected, start, end);
+		}
+	}
+}
+
+/* Test usage of copy_struct_from_user(). */
+static void usercopy_test_copy_struct_from_user(struct kunit *test)
+{
+	char *umem_src = NULL, *expected = NULL;
+	struct usercopy_test_priv *priv = test->priv;
+	char __user *umem = priv->umem;
+	char *kmem = priv->kmem;
+	size_t size = priv->size;
+	size_t ksize, usize;
+
+	umem_src = kunit_kmalloc(test, size, GFP_KERNEL);
+	KUNIT_ASSERT_NOT_ERR_OR_NULL(test, umem_src);
+
+	expected = kunit_kmalloc(test, size, GFP_KERNEL);
+	KUNIT_ASSERT_NOT_ERR_OR_NULL(test, expected);
+
+	/* Fill umem with a fixed byte pattern. */
+	memset(umem_src, 0x3e, size);
+	KUNIT_ASSERT_EQ_MSG(test, copy_to_user(umem, umem_src, size), 0,
+		    "legitimate copy_to_user failed");
+
+	/* Check basic case -- (usize == ksize). */
+	ksize = size;
+	usize = size;
+
+	memcpy(expected, umem_src, ksize);
+
+	memset(kmem, 0x0, size);
+	KUNIT_EXPECT_EQ_MSG(test, copy_struct_from_user(kmem, ksize, umem, usize), 0,
+		    "copy_struct_from_user(usize == ksize) failed");
+	KUNIT_EXPECT_MEMEQ_MSG(test, kmem, expected, ksize,
+		    "copy_struct_from_user(usize == ksize) gives unexpected copy");
+
+	/* Old userspace case -- (usize < ksize). */
+	ksize = size;
+	usize = size / 2;
+
+	memcpy(expected, umem_src, usize);
+	memset(expected + usize, 0x0, ksize - usize);
+
+	memset(kmem, 0x0, size);
+	KUNIT_EXPECT_EQ_MSG(test, copy_struct_from_user(kmem, ksize, umem, usize), 0,
+		    "copy_struct_from_user(usize < ksize) failed");
+	KUNIT_EXPECT_MEMEQ_MSG(test, kmem, expected, ksize,
+		    "copy_struct_from_user(usize < ksize) gives unexpected copy");
+
+	/* New userspace (-E2BIG) case -- (usize > ksize). */
+	ksize = size / 2;
+	usize = size;
+
+	memset(kmem, 0x0, size);
+	KUNIT_EXPECT_EQ_MSG(test, copy_struct_from_user(kmem, ksize, umem, usize), -E2BIG,
+		    "copy_struct_from_user(usize > ksize) didn't give E2BIG");
+
+	/* New userspace (success) case -- (usize > ksize). */
+	ksize = size / 2;
+	usize = size;
+
+	memcpy(expected, umem_src, ksize);
+	KUNIT_EXPECT_EQ_MSG(test, clear_user(umem + ksize, usize - ksize), 0,
+		    "legitimate clear_user failed");
+
+	memset(kmem, 0x0, size);
+	KUNIT_EXPECT_EQ_MSG(test, copy_struct_from_user(kmem, ksize, umem, usize), 0,
+		    "copy_struct_from_user(usize > ksize) failed");
+	KUNIT_EXPECT_MEMEQ_MSG(test, kmem, expected, ksize,
+		    "copy_struct_from_user(usize > ksize) gives unexpected copy");
+}
+
+/*
+ * Legitimate usage: none of these copies should fail.
+ */
+static void usercopy_test_valid(struct kunit *test)
+{
+	struct usercopy_test_priv *priv = test->priv;
+	char __user *usermem = priv->umem;
+	char *kmem = priv->kmem;
+
+	memset(kmem, 0x3a, PAGE_SIZE * 2);
+	KUNIT_EXPECT_EQ_MSG(test, 0, copy_to_user(usermem, kmem, PAGE_SIZE),
+	     "legitimate copy_to_user failed");
+	memset(kmem, 0x0, PAGE_SIZE);
+	KUNIT_EXPECT_EQ_MSG(test, 0, copy_from_user(kmem, usermem, PAGE_SIZE),
+	     "legitimate copy_from_user failed");
+	KUNIT_EXPECT_MEMEQ_MSG(test, kmem, kmem + PAGE_SIZE, PAGE_SIZE,
+	     "legitimate usercopy failed to copy data");
+
+#define test_legit(size, check)						\
+	do {								\
+		size val_##size = (check);				\
+		KUNIT_EXPECT_EQ_MSG(test, 0,				\
+			put_user(val_##size, (size __user *)usermem),	\
+			"legitimate put_user (" #size ") failed");	\
+		val_##size = 0;						\
+		KUNIT_EXPECT_EQ_MSG(test, 0,				\
+			get_user(val_##size, (size __user *)usermem),	\
+			"legitimate get_user (" #size ") failed");	\
+		KUNIT_EXPECT_EQ_MSG(test, val_##size, check,		\
+			"legitimate get_user (" #size ") failed to do copy"); \
+	} while (0)
+
+	test_legit(u8,  0x5a);
+	test_legit(u16, 0x5a5b);
+	test_legit(u32, 0x5a5b5c5d);
+#ifdef TEST_U64
+	test_legit(u64, 0x5a5b5c5d6a6b6c6d);
+#endif
+#undef test_legit
+}
+
+/*
+ * Invalid usage: none of these copies should succeed.
+ */
+static void usercopy_test_invalid(struct kunit *test)
+{
+	struct usercopy_test_priv *priv = test->priv;
+	char __user *usermem = priv->umem;
+	char *bad_usermem = (char *)usermem;
+	char *kmem = priv->kmem;
+	u64 *kmem_u64 = (u64 *)kmem;
+
+	if (IS_ENABLED(CONFIG_ALTERNATE_USER_ADDRESS_SPACE) ||
+	    !IS_ENABLED(CONFIG_MMU)) {
+		kunit_skip(test, "Testing for kernel/userspace address confusion is only sensible on architectures with a shared address space");
+		return;
+	}
+
+	/* Prepare kernel memory with check values. */
+	memset(kmem, 0x5a, PAGE_SIZE);
+	memset(kmem + PAGE_SIZE, 0, PAGE_SIZE);
+
+	/* Reject kernel-to-kernel copies through copy_from_user(). */
+	KUNIT_EXPECT_NE_MSG(test, copy_from_user(kmem, (char __user *)(kmem + PAGE_SIZE),
+						 PAGE_SIZE), 0,
+		    "illegal all-kernel copy_from_user passed");
+
+	/* Destination half of buffer should have been zeroed. */
+	KUNIT_EXPECT_MEMEQ_MSG(test, kmem + PAGE_SIZE, kmem, PAGE_SIZE,
+		    "zeroing failure for illegal all-kernel copy_from_user");
+
+#if 0
+	/*
+	 * When running with SMAP/PAN/etc, this will Oops the kernel
+	 * due to the zeroing of userspace memory on failure. This needs
+	 * to be tested in LKDTM instead, since this test module does not
+	 * expect to explode.
+	 */
+	KUNIT_EXPECT_NE_MSG(test, copy_from_user(bad_usermem, (char __user *)kmem,
+						 PAGE_SIZE), 0,
+		    "illegal reversed copy_from_user passed");
+#endif
+	KUNIT_EXPECT_NE_MSG(test, copy_to_user((char __user *)kmem, kmem + PAGE_SIZE,
+					       PAGE_SIZE), 0,
+		    "illegal all-kernel copy_to_user passed");
+
+	KUNIT_EXPECT_NE_MSG(test, copy_to_user((char __user *)kmem, bad_usermem,
+					       PAGE_SIZE), 0,
+		    "illegal reversed copy_to_user passed");
+
+#define test_illegal(size, check)							\
+	do {										\
+		size val_##size = (check);						\
+		/* get_user() */							\
+		KUNIT_EXPECT_NE_MSG(test, get_user(val_##size, (size __user *)kmem), 0,	\
+		    "illegal get_user (" #size ") passed");				\
+		KUNIT_EXPECT_EQ_MSG(test, val_##size, 0,				\
+		    "zeroing failure for illegal get_user (" #size ")");		\
+		/* put_user() */							\
+		*kmem_u64 = 0xF09FA4AFF09FA4AF;						\
+		KUNIT_EXPECT_NE_MSG(test, put_user(val_##size, (size __user *)kmem), 0,	\
+		    "illegal put_user (" #size ") passed");				\
+		KUNIT_EXPECT_EQ_MSG(test, *kmem_u64, 0xF09FA4AFF09FA4AF,		\
+		    "illegal put_user (" #size ") wrote to kernel memory!");		\
+	} while (0)
+
+	test_illegal(u8,  0x5a);
+	test_illegal(u16, 0x5a5b);
+	test_illegal(u32, 0x5a5b5c5d);
+#ifdef TEST_U64
+	test_illegal(u64, 0x5a5b5c5d6a6b6c6d);
+#endif
+#undef test_illegal
+}
+
+static int usercopy_test_init(struct kunit *test)
+{
+	struct usercopy_test_priv *priv;
+	unsigned long user_addr;
+
+	if (!IS_ENABLED(CONFIG_MMU)) {
+		kunit_skip(test, "Userspace allocation testing not available on non-MMU systems");
+		return 0;
+	}
+
+	priv = kunit_kzalloc(test, sizeof(*priv), GFP_KERNEL);
+	KUNIT_ASSERT_NOT_ERR_OR_NULL(test, priv);
+	test->priv = priv;
+	priv->size = PAGE_SIZE * 2;
+
+	priv->kmem = kunit_kmalloc(test, priv->size, GFP_KERNEL);
+	KUNIT_ASSERT_NOT_ERR_OR_NULL(test, priv->kmem);
+
+	user_addr = kunit_vm_mmap(test, NULL, 0, priv->size,
+			    PROT_READ | PROT_WRITE | PROT_EXEC,
+			    MAP_ANONYMOUS | MAP_PRIVATE, 0);
+	KUNIT_ASSERT_NE_MSG(test, user_addr, 0,
+		"Could not create userspace mm");
+	KUNIT_ASSERT_LT_MSG(test, user_addr, (unsigned long)TASK_SIZE,
+		"Failed to allocate user memory");
+	priv->umem = (char __user *)user_addr;
+
+	return 0;
+}
+
+static struct kunit_case usercopy_test_cases[] = {
+	KUNIT_CASE(usercopy_test_valid),
+	KUNIT_CASE(usercopy_test_invalid),
+	KUNIT_CASE(usercopy_test_check_nonzero_user),
+	KUNIT_CASE(usercopy_test_copy_struct_from_user),
+	{}
+};
+
+static struct kunit_suite usercopy_test_suite = {
+	.name = "usercopy",
+	.init = usercopy_test_init,
+	.test_cases = usercopy_test_cases,
+};
+
+kunit_test_suites(&usercopy_test_suite);
+MODULE_AUTHOR("Kees Cook <kees@kernel.org>");
+MODULE_DESCRIPTION("Kernel module for testing copy_to/from_user infrastructure");
+MODULE_LICENSE("GPL");