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, 225 insertions, 0 deletions

diff --git a/drivers/crypto/omap-crypto.c b/drivers/crypto/omap-crypto.c
new file mode 100644
index 000000000..7bd6869c2
--- /dev/null
+++ b/drivers/crypto/omap-crypto.c
@@ -0,0 +1,225 @@
+// SPDX-License-Identifier: GPL-2.0-only
+/*
+ * OMAP Crypto driver common support routines.
+ *
+ * Copyright (c) 2017 Texas Instruments Incorporated
+ *   Tero Kristo <t-kristo@ti.com>
+ */
+
+#include <linux/module.h>
+#include <linux/kernel.h>
+#include <linux/scatterlist.h>
+#include <crypto/scatterwalk.h>
+
+#include "omap-crypto.h"
+
+static int omap_crypto_copy_sg_lists(int total, int bs,
+				     struct scatterlist **sg,
+				     struct scatterlist *new_sg, u16 flags)
+{
+	int n = sg_nents(*sg);
+	struct scatterlist *tmp;
+
+	if (!(flags & OMAP_CRYPTO_FORCE_SINGLE_ENTRY)) {
+		new_sg = kmalloc_objs(*new_sg, n);
+		if (!new_sg)
+			return -ENOMEM;
+
+		sg_init_table(new_sg, n);
+	}
+
+	tmp = new_sg;
+
+	while (*sg && total) {
+		int len = (*sg)->length;
+
+		if (total < len)
+			len = total;
+
+		if (len > 0) {
+			total -= len;
+			sg_set_page(tmp, sg_page(*sg), len, (*sg)->offset);
+			if (total <= 0)
+				sg_mark_end(tmp);
+			tmp = sg_next(tmp);
+		}
+
+		*sg = sg_next(*sg);
+	}
+
+	*sg = new_sg;
+
+	return 0;
+}
+
+static int omap_crypto_copy_sgs(int total, int bs, struct scatterlist **sg,
+				struct scatterlist *new_sg, u16 flags)
+{
+	void *buf;
+	int pages;
+	int new_len;
+
+	new_len = ALIGN(total, bs);
+	pages = get_order(new_len);
+
+	buf = (void *)__get_free_pages(GFP_ATOMIC, pages);
+	if (!buf) {
+		pr_err("%s: Couldn't allocate pages for unaligned cases.\n",
+		       __func__);
+		return -ENOMEM;
+	}
+
+	if (flags & OMAP_CRYPTO_COPY_DATA) {
+		scatterwalk_map_and_copy(buf, *sg, 0, total, 0);
+		if (flags & OMAP_CRYPTO_ZERO_BUF)
+			memset(buf + total, 0, new_len - total);
+	}
+
+	if (!(flags & OMAP_CRYPTO_FORCE_SINGLE_ENTRY))
+		sg_init_table(new_sg, 1);
+
+	sg_set_buf(new_sg, buf, new_len);
+
+	*sg = new_sg;
+
+	return 0;
+}
+
+static int omap_crypto_check_sg(struct scatterlist *sg, int total, int bs,
+				u16 flags)
+{
+	int len = 0;
+	int num_sg = 0;
+
+	if (!IS_ALIGNED(total, bs))
+		return OMAP_CRYPTO_NOT_ALIGNED;
+
+	while (sg) {
+		num_sg++;
+
+		if (!IS_ALIGNED(sg->offset, 4))
+			return OMAP_CRYPTO_NOT_ALIGNED;
+		if (!IS_ALIGNED(sg->length, bs))
+			return OMAP_CRYPTO_NOT_ALIGNED;
+#ifdef CONFIG_ZONE_DMA
+		if (page_zonenum(sg_page(sg)) != ZONE_DMA)
+			return OMAP_CRYPTO_NOT_ALIGNED;
+#endif
+
+		len += sg->length;
+		sg = sg_next(sg);
+
+		if (len >= total)
+			break;
+	}
+
+	if ((flags & OMAP_CRYPTO_FORCE_SINGLE_ENTRY) && num_sg > 1)
+		return OMAP_CRYPTO_NOT_ALIGNED;
+
+	if (len != total)
+		return OMAP_CRYPTO_BAD_DATA_LENGTH;
+
+	return 0;
+}
+
+int omap_crypto_align_sg(struct scatterlist **sg, int total, int bs,
+			 struct scatterlist *new_sg, u16 flags,
+			 u8 flags_shift, unsigned long *dd_flags)
+{
+	int ret;
+
+	*dd_flags &= ~(OMAP_CRYPTO_COPY_MASK << flags_shift);
+
+	if (flags & OMAP_CRYPTO_FORCE_COPY)
+		ret = OMAP_CRYPTO_NOT_ALIGNED;
+	else
+		ret = omap_crypto_check_sg(*sg, total, bs, flags);
+
+	if (ret == OMAP_CRYPTO_NOT_ALIGNED) {
+		ret = omap_crypto_copy_sgs(total, bs, sg, new_sg, flags);
+		if (ret)
+			return ret;
+		*dd_flags |= OMAP_CRYPTO_DATA_COPIED << flags_shift;
+	} else if (ret == OMAP_CRYPTO_BAD_DATA_LENGTH) {
+		ret = omap_crypto_copy_sg_lists(total, bs, sg, new_sg, flags);
+		if (ret)
+			return ret;
+		if (!(flags & OMAP_CRYPTO_FORCE_SINGLE_ENTRY))
+			*dd_flags |= OMAP_CRYPTO_SG_COPIED << flags_shift;
+	} else if (flags & OMAP_CRYPTO_FORCE_SINGLE_ENTRY) {
+		sg_set_buf(new_sg, sg_virt(*sg), (*sg)->length);
+	}
+
+	return 0;
+}
+EXPORT_SYMBOL_GPL(omap_crypto_align_sg);
+
+static void omap_crypto_copy_data(struct scatterlist *src,
+				  struct scatterlist *dst,
+				  int offset, int len)
+{
+	int amt;
+	void *srcb, *dstb;
+	int srco = 0, dsto = offset;
+
+	while (src && dst && len) {
+		if (srco >= src->length) {
+			srco -= src->length;
+			src = sg_next(src);
+			continue;
+		}
+
+		if (dsto >= dst->length) {
+			dsto -= dst->length;
+			dst = sg_next(dst);
+			continue;
+		}
+
+		amt = min(src->length - srco, dst->length - dsto);
+		amt = min(len, amt);
+
+		srcb = kmap_atomic(sg_page(src)) + srco + src->offset;
+		dstb = kmap_atomic(sg_page(dst)) + dsto + dst->offset;
+
+		memcpy(dstb, srcb, amt);
+
+		flush_dcache_page(sg_page(dst));
+
+		kunmap_atomic(srcb);
+		kunmap_atomic(dstb);
+
+		srco += amt;
+		dsto += amt;
+		len -= amt;
+	}
+}
+
+void omap_crypto_cleanup(struct scatterlist *sg, struct scatterlist *orig,
+			 int offset, int len, u8 flags_shift,
+			 unsigned long flags)
+{
+	void *buf;
+	int pages;
+
+	flags >>= flags_shift;
+	flags &= OMAP_CRYPTO_COPY_MASK;
+
+	if (!flags)
+		return;
+
+	buf = sg_virt(sg);
+	pages = get_order(len);
+
+	if (orig && (flags & OMAP_CRYPTO_DATA_COPIED))
+		omap_crypto_copy_data(sg, orig, offset, len);
+
+	if (flags & OMAP_CRYPTO_DATA_COPIED)
+		free_pages((unsigned long)buf, pages);
+	else if (flags & OMAP_CRYPTO_SG_COPIED)
+		kfree(sg);
+}
+EXPORT_SYMBOL_GPL(omap_crypto_cleanup);
+
+MODULE_DESCRIPTION("OMAP crypto support library.");
+MODULE_LICENSE("GPL v2");
+MODULE_AUTHOR("Tero Kristo <t-kristo@ti.com>");