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, 402 insertions, 0 deletions

diff --git a/crypto/scompress.c b/crypto/scompress.c
new file mode 100644
index 000000000..de5422720
--- /dev/null
+++ b/crypto/scompress.c
@@ -0,0 +1,402 @@
+// SPDX-License-Identifier: GPL-2.0-or-later
+/*
+ * Synchronous Compression operations
+ *
+ * Copyright 2015 LG Electronics Inc.
+ * Copyright (c) 2016, Intel Corporation
+ * Author: Giovanni Cabiddu <giovanni.cabiddu@intel.com>
+ */
+
+#include <crypto/internal/scompress.h>
+#include <crypto/scatterwalk.h>
+#include <linux/cpumask.h>
+#include <linux/cryptouser.h>
+#include <linux/err.h>
+#include <linux/highmem.h>
+#include <linux/kernel.h>
+#include <linux/module.h>
+#include <linux/overflow.h>
+#include <linux/scatterlist.h>
+#include <linux/seq_file.h>
+#include <linux/slab.h>
+#include <linux/string.h>
+#include <linux/workqueue.h>
+#include <net/netlink.h>
+
+#include "compress.h"
+
+struct scomp_scratch {
+	spinlock_t	lock;
+	union {
+		void	*src __guarded_by(&lock);
+		unsigned long saddr __guarded_by(&lock);
+	};
+};
+
+static DEFINE_PER_CPU(struct scomp_scratch, scomp_scratch) = {
+	.lock = __SPIN_LOCK_UNLOCKED(scomp_scratch.lock),
+};
+
+static const struct crypto_type crypto_scomp_type;
+static DEFINE_MUTEX(scomp_lock);
+static int scomp_scratch_users __guarded_by(&scomp_lock);
+
+static cpumask_t scomp_scratch_want;
+static void scomp_scratch_workfn(struct work_struct *work);
+static DECLARE_WORK(scomp_scratch_work, scomp_scratch_workfn);
+
+static int __maybe_unused crypto_scomp_report(
+	struct sk_buff *skb, struct crypto_alg *alg)
+{
+	struct crypto_report_comp rscomp = {
+		.type = "scomp",
+	};
+
+	return nla_put(skb, CRYPTOCFGA_REPORT_COMPRESS,
+		       sizeof(rscomp), &rscomp);
+}
+
+static void __maybe_unused crypto_scomp_show(struct seq_file *m,
+					     struct crypto_alg *alg)
+{
+	seq_puts(m, "type         : scomp\n");
+}
+
+static void crypto_scomp_free_scratches(void)
+	__context_unsafe(/* frees @scratch */)
+{
+	struct scomp_scratch *scratch;
+	int i;
+
+	for_each_possible_cpu(i) {
+		scratch = per_cpu_ptr(&scomp_scratch, i);
+
+		free_page(scratch->saddr);
+		scratch->src = NULL;
+	}
+}
+
+static int scomp_alloc_scratch(struct scomp_scratch *scratch, int cpu)
+{
+	int node = cpu_to_node(cpu);
+	struct page *page;
+
+	page = alloc_pages_node(node, GFP_KERNEL, 0);
+	if (!page)
+		return -ENOMEM;
+	spin_lock_bh(&scratch->lock);
+	scratch->src = page_address(page);
+	spin_unlock_bh(&scratch->lock);
+	return 0;
+}
+
+static void scomp_scratch_workfn(struct work_struct *work)
+{
+	int cpu;
+
+	for_each_cpu(cpu, &scomp_scratch_want) {
+		struct scomp_scratch *scratch;
+
+		scratch = per_cpu_ptr(&scomp_scratch, cpu);
+		if (context_unsafe(scratch->src))
+			continue;
+		if (scomp_alloc_scratch(scratch, cpu))
+			break;
+
+		cpumask_clear_cpu(cpu, &scomp_scratch_want);
+	}
+}
+
+static int crypto_scomp_alloc_scratches(void)
+	__context_unsafe(/* allocates @scratch */)
+{
+	unsigned int i = cpumask_first(cpu_possible_mask);
+	struct scomp_scratch *scratch;
+
+	scratch = per_cpu_ptr(&scomp_scratch, i);
+	return scomp_alloc_scratch(scratch, i);
+}
+
+static int crypto_scomp_init_tfm(struct crypto_tfm *tfm)
+{
+	struct scomp_alg *alg = crypto_scomp_alg(__crypto_scomp_tfm(tfm));
+	int ret = 0;
+
+	mutex_lock(&scomp_lock);
+	ret = crypto_acomp_alloc_streams(&alg->streams);
+	if (ret)
+		goto unlock;
+	if (!scomp_scratch_users++) {
+		ret = crypto_scomp_alloc_scratches();
+		if (ret)
+			scomp_scratch_users--;
+	}
+unlock:
+	mutex_unlock(&scomp_lock);
+
+	return ret;
+}
+
+#define scomp_lock_scratch(...) __acquire_ret(_scomp_lock_scratch(__VA_ARGS__), &__ret->lock)
+static struct scomp_scratch *_scomp_lock_scratch(void) __acquires_ret
+{
+	int cpu = raw_smp_processor_id();
+	struct scomp_scratch *scratch;
+
+	scratch = per_cpu_ptr(&scomp_scratch, cpu);
+	spin_lock(&scratch->lock);
+	if (likely(scratch->src))
+		return scratch;
+	spin_unlock(&scratch->lock);
+
+	cpumask_set_cpu(cpu, &scomp_scratch_want);
+	schedule_work(&scomp_scratch_work);
+
+	scratch = per_cpu_ptr(&scomp_scratch, cpumask_first(cpu_possible_mask));
+	spin_lock(&scratch->lock);
+	return scratch;
+}
+
+static inline void scomp_unlock_scratch(struct scomp_scratch *scratch)
+	__releases(&scratch->lock)
+{
+	spin_unlock(&scratch->lock);
+}
+
+static int scomp_acomp_comp_decomp(struct acomp_req *req, int dir)
+{
+	struct crypto_acomp *tfm = crypto_acomp_reqtfm(req);
+	struct crypto_scomp **tfm_ctx = acomp_tfm_ctx(tfm);
+	bool src_isvirt = acomp_request_src_isvirt(req);
+	bool dst_isvirt = acomp_request_dst_isvirt(req);
+	struct crypto_scomp *scomp = *tfm_ctx;
+	unsigned int slen = req->slen;
+	unsigned int dlen = req->dlen;
+	struct page *spage, *dpage;
+	unsigned int n;
+	const u8 *src;
+	size_t soff;
+	size_t doff;
+	u8 *dst;
+	int ret;
+
+	if (!req->src || !slen)
+		return -EINVAL;
+
+	if (!req->dst || !dlen)
+		return -EINVAL;
+
+	if (dst_isvirt)
+		dst = req->dvirt;
+	else {
+		if (dlen <= req->dst->length) {
+			dpage = sg_page(req->dst);
+			doff = req->dst->offset;
+		} else
+			return -ENOSYS;
+
+		dpage += doff / PAGE_SIZE;
+		doff = offset_in_page(doff);
+
+		n = (dlen - 1) / PAGE_SIZE;
+		n += (offset_in_page(dlen - 1) + doff) / PAGE_SIZE;
+		if (PageHighMem(dpage + n) &&
+		    size_add(doff, dlen) > PAGE_SIZE)
+			return -ENOSYS;
+		dst = kmap_local_page(dpage) + doff;
+	}
+
+	if (src_isvirt)
+		src = req->svirt;
+	else {
+		src = NULL;
+		do {
+			if (slen <= req->src->length) {
+				spage = sg_page(req->src);
+				soff = req->src->offset;
+			} else
+				break;
+
+			spage = spage + soff / PAGE_SIZE;
+			soff = offset_in_page(soff);
+
+			n = (slen - 1) / PAGE_SIZE;
+			n += (offset_in_page(slen - 1) + soff) / PAGE_SIZE;
+			if (PageHighMem(spage + n) &&
+			    size_add(soff, slen) > PAGE_SIZE)
+				break;
+			src = kmap_local_page(spage) + soff;
+		} while (0);
+	}
+
+	struct crypto_acomp_stream *stream = crypto_acomp_lock_stream_bh(&crypto_scomp_alg(scomp)->streams);
+
+	if (!src_isvirt && !src) {
+		struct scomp_scratch *scratch = scomp_lock_scratch();
+		const u8 *src = scratch->src;
+
+		memcpy_from_sglist(scratch->src, req->src, 0, slen);
+
+		if (dir)
+			ret = crypto_scomp_compress(scomp, src, slen,
+						    dst, &dlen, stream->ctx);
+		else
+			ret = crypto_scomp_decompress(scomp, src, slen,
+						      dst, &dlen, stream->ctx);
+
+		scomp_unlock_scratch(scratch);
+	} else if (dir)
+		ret = crypto_scomp_compress(scomp, src, slen,
+					    dst, &dlen, stream->ctx);
+	else
+		ret = crypto_scomp_decompress(scomp, src, slen,
+					      dst, &dlen, stream->ctx);
+
+	crypto_acomp_unlock_stream_bh(stream);
+
+	req->dlen = dlen;
+
+	if (!src_isvirt && src)
+		kunmap_local(src);
+	if (!dst_isvirt) {
+		kunmap_local(dst);
+		dlen += doff;
+		for (;;) {
+			flush_dcache_page(dpage);
+			if (dlen <= PAGE_SIZE)
+				break;
+			dlen -= PAGE_SIZE;
+			dpage++;
+		}
+	}
+
+	return ret;
+}
+
+static int scomp_acomp_compress(struct acomp_req *req)
+{
+	return scomp_acomp_comp_decomp(req, 1);
+}
+
+static int scomp_acomp_decompress(struct acomp_req *req)
+{
+	return scomp_acomp_comp_decomp(req, 0);
+}
+
+static void crypto_exit_scomp_ops_async(struct crypto_tfm *tfm)
+{
+	struct crypto_scomp **ctx = crypto_tfm_ctx(tfm);
+
+	crypto_free_scomp(*ctx);
+
+	flush_work(&scomp_scratch_work);
+	mutex_lock(&scomp_lock);
+	if (!--scomp_scratch_users)
+		crypto_scomp_free_scratches();
+	mutex_unlock(&scomp_lock);
+}
+
+int crypto_init_scomp_ops_async(struct crypto_tfm *tfm)
+{
+	struct crypto_alg *calg = tfm->__crt_alg;
+	struct crypto_acomp *crt = __crypto_acomp_tfm(tfm);
+	struct crypto_scomp **ctx = crypto_tfm_ctx(tfm);
+	struct crypto_scomp *scomp;
+
+	if (!crypto_mod_get(calg))
+		return -EAGAIN;
+
+	scomp = crypto_create_tfm(calg, &crypto_scomp_type);
+	if (IS_ERR(scomp)) {
+		crypto_mod_put(calg);
+		return PTR_ERR(scomp);
+	}
+
+	*ctx = scomp;
+	tfm->exit = crypto_exit_scomp_ops_async;
+
+	crt->compress = scomp_acomp_compress;
+	crt->decompress = scomp_acomp_decompress;
+
+	return 0;
+}
+
+static void crypto_scomp_destroy(struct crypto_alg *alg)
+{
+	struct scomp_alg *scomp = __crypto_scomp_alg(alg);
+
+	crypto_acomp_free_streams(&scomp->streams);
+}
+
+static const struct crypto_type crypto_scomp_type = {
+	.extsize = crypto_alg_extsize,
+	.init_tfm = crypto_scomp_init_tfm,
+	.destroy = crypto_scomp_destroy,
+#ifdef CONFIG_PROC_FS
+	.show = crypto_scomp_show,
+#endif
+#if IS_ENABLED(CONFIG_CRYPTO_USER)
+	.report = crypto_scomp_report,
+#endif
+	.maskclear = ~CRYPTO_ALG_TYPE_MASK,
+	.maskset = CRYPTO_ALG_TYPE_MASK,
+	.type = CRYPTO_ALG_TYPE_SCOMPRESS,
+	.tfmsize = offsetof(struct crypto_scomp, base),
+	.algsize = offsetof(struct scomp_alg, base),
+};
+
+static void scomp_prepare_alg(struct scomp_alg *alg)
+{
+	struct crypto_alg *base = &alg->calg.base;
+
+	comp_prepare_alg(&alg->calg);
+
+	base->cra_flags |= CRYPTO_ALG_REQ_VIRT;
+}
+
+int crypto_register_scomp(struct scomp_alg *alg)
+{
+	struct crypto_alg *base = &alg->calg.base;
+
+	scomp_prepare_alg(alg);
+
+	base->cra_type = &crypto_scomp_type;
+	base->cra_flags |= CRYPTO_ALG_TYPE_SCOMPRESS;
+
+	return crypto_register_alg(base);
+}
+EXPORT_SYMBOL_GPL(crypto_register_scomp);
+
+void crypto_unregister_scomp(struct scomp_alg *alg)
+{
+	crypto_unregister_alg(&alg->base);
+}
+EXPORT_SYMBOL_GPL(crypto_unregister_scomp);
+
+int crypto_register_scomps(struct scomp_alg *algs, int count)
+{
+	int i, ret;
+
+	for (i = 0; i < count; i++) {
+		ret = crypto_register_scomp(&algs[i]);
+		if (ret) {
+			crypto_unregister_scomps(algs, i);
+			return ret;
+		}
+	}
+
+	return 0;
+}
+EXPORT_SYMBOL_GPL(crypto_register_scomps);
+
+void crypto_unregister_scomps(struct scomp_alg *algs, int count)
+{
+	int i;
+
+	for (i = count - 1; i >= 0; --i)
+		crypto_unregister_scomp(&algs[i]);
+}
+EXPORT_SYMBOL_GPL(crypto_unregister_scomps);
+
+MODULE_LICENSE("GPL");
+MODULE_DESCRIPTION("Synchronous compression type");