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, 276 insertions, 0 deletions

diff --git a/drivers/crypto/qcom-rng.c b/drivers/crypto/qcom-rng.c
new file mode 100644
index 000000000..150e5802e
--- /dev/null
+++ b/drivers/crypto/qcom-rng.c
@@ -0,0 +1,276 @@
+// SPDX-License-Identifier: GPL-2.0
+// Copyright (c) 2017-18 Linaro Limited
+//
+// Based on msm-rng.c and downstream driver
+
+#include <crypto/internal/rng.h>
+#include <linux/acpi.h>
+#include <linux/clk.h>
+#include <linux/crypto.h>
+#include <linux/hw_random.h>
+#include <linux/io.h>
+#include <linux/iopoll.h>
+#include <linux/kernel.h>
+#include <linux/module.h>
+#include <linux/of.h>
+#include <linux/platform_device.h>
+
+/* Device specific register offsets */
+#define PRNG_DATA_OUT		0x0000
+#define PRNG_STATUS		0x0004
+#define PRNG_LFSR_CFG		0x0100
+#define PRNG_CONFIG		0x0104
+
+/* Device specific register masks and config values */
+#define PRNG_LFSR_CFG_MASK	0x0000ffff
+#define PRNG_LFSR_CFG_CLOCKS	0x0000dddd
+#define PRNG_CONFIG_HW_ENABLE	BIT(1)
+#define PRNG_STATUS_DATA_AVAIL	BIT(0)
+
+#define WORD_SZ			4
+
+#define QCOM_TRNG_QUALITY	1024
+
+struct qcom_rng {
+	struct mutex lock;
+	void __iomem *base;
+	struct clk *clk;
+	struct hwrng hwrng;
+	struct qcom_rng_match_data *match_data;
+};
+
+struct qcom_rng_ctx {
+	struct qcom_rng *rng;
+};
+
+struct qcom_rng_match_data {
+	bool skip_init;
+	bool hwrng_support;
+};
+
+static struct qcom_rng *qcom_rng_dev;
+
+static int qcom_rng_read(struct qcom_rng *rng, u8 *data, unsigned int max)
+{
+	unsigned int currsize = 0;
+	u32 val;
+	int ret;
+
+	/* read random data from hardware */
+	do {
+		ret = readl_poll_timeout(rng->base + PRNG_STATUS, val,
+					 val & PRNG_STATUS_DATA_AVAIL,
+					 200, 10000);
+		if (ret)
+			return ret;
+
+		val = readl_relaxed(rng->base + PRNG_DATA_OUT);
+		if (!val)
+			return -EINVAL;
+
+		if ((max - currsize) >= WORD_SZ) {
+			memcpy(data, &val, WORD_SZ);
+			data += WORD_SZ;
+			currsize += WORD_SZ;
+		} else {
+			/* copy only remaining bytes */
+			memcpy(data, &val, max - currsize);
+			currsize = max;
+		}
+	} while (currsize < max);
+
+	return currsize;
+}
+
+static int qcom_rng_generate(struct crypto_rng *tfm,
+			     const u8 *src, unsigned int slen,
+			     u8 *dstn, unsigned int dlen)
+{
+	struct qcom_rng_ctx *ctx = crypto_rng_ctx(tfm);
+	struct qcom_rng *rng = ctx->rng;
+	int ret;
+
+	ret = clk_prepare_enable(rng->clk);
+	if (ret)
+		return ret;
+
+	mutex_lock(&rng->lock);
+
+	ret = qcom_rng_read(rng, dstn, dlen);
+
+	mutex_unlock(&rng->lock);
+	clk_disable_unprepare(rng->clk);
+
+	if (ret >= 0)
+		ret = 0;
+
+	return ret;
+}
+
+static int qcom_rng_seed(struct crypto_rng *tfm, const u8 *seed,
+			 unsigned int slen)
+{
+	return 0;
+}
+
+static int qcom_hwrng_read(struct hwrng *hwrng, void *data, size_t max, bool wait)
+{
+	struct qcom_rng *qrng = container_of(hwrng, struct qcom_rng, hwrng);
+
+	return qcom_rng_read(qrng, data, max);
+}
+
+static int qcom_rng_enable(struct qcom_rng *rng)
+{
+	u32 val;
+	int ret;
+
+	ret = clk_prepare_enable(rng->clk);
+	if (ret)
+		return ret;
+
+	/* Enable PRNG only if it is not already enabled */
+	val = readl_relaxed(rng->base + PRNG_CONFIG);
+	if (val & PRNG_CONFIG_HW_ENABLE)
+		goto already_enabled;
+
+	val = readl_relaxed(rng->base + PRNG_LFSR_CFG);
+	val &= ~PRNG_LFSR_CFG_MASK;
+	val |= PRNG_LFSR_CFG_CLOCKS;
+	writel(val, rng->base + PRNG_LFSR_CFG);
+
+	val = readl_relaxed(rng->base + PRNG_CONFIG);
+	val |= PRNG_CONFIG_HW_ENABLE;
+	writel(val, rng->base + PRNG_CONFIG);
+
+already_enabled:
+	clk_disable_unprepare(rng->clk);
+
+	return 0;
+}
+
+static int qcom_rng_init(struct crypto_tfm *tfm)
+{
+	struct qcom_rng_ctx *ctx = crypto_tfm_ctx(tfm);
+
+	ctx->rng = qcom_rng_dev;
+
+	if (!ctx->rng->match_data->skip_init)
+		return qcom_rng_enable(ctx->rng);
+
+	return 0;
+}
+
+static struct rng_alg qcom_rng_alg = {
+	.generate	= qcom_rng_generate,
+	.seed		= qcom_rng_seed,
+	.seedsize	= 0,
+	.base		= {
+		.cra_name		= "stdrng",
+		.cra_driver_name	= "qcom-rng",
+		.cra_flags		= CRYPTO_ALG_TYPE_RNG,
+		.cra_priority		= 300,
+		.cra_ctxsize		= sizeof(struct qcom_rng_ctx),
+		.cra_module		= THIS_MODULE,
+		.cra_init		= qcom_rng_init,
+	}
+};
+
+static int qcom_rng_probe(struct platform_device *pdev)
+{
+	struct qcom_rng *rng;
+	int ret;
+
+	rng = devm_kzalloc(&pdev->dev, sizeof(*rng), GFP_KERNEL);
+	if (!rng)
+		return -ENOMEM;
+
+	platform_set_drvdata(pdev, rng);
+	mutex_init(&rng->lock);
+
+	rng->base = devm_platform_ioremap_resource(pdev, 0);
+	if (IS_ERR(rng->base))
+		return PTR_ERR(rng->base);
+
+	rng->clk = devm_clk_get_optional(&pdev->dev, "core");
+	if (IS_ERR(rng->clk))
+		return PTR_ERR(rng->clk);
+
+	rng->match_data = (struct qcom_rng_match_data *)device_get_match_data(&pdev->dev);
+
+	qcom_rng_dev = rng;
+	ret = crypto_register_rng(&qcom_rng_alg);
+	if (ret) {
+		dev_err(&pdev->dev, "Register crypto rng failed: %d\n", ret);
+		qcom_rng_dev = NULL;
+		return ret;
+	}
+
+	if (rng->match_data->hwrng_support) {
+		rng->hwrng.name = "qcom_hwrng";
+		rng->hwrng.read = qcom_hwrng_read;
+		rng->hwrng.quality = QCOM_TRNG_QUALITY;
+		ret = devm_hwrng_register(&pdev->dev, &rng->hwrng);
+		if (ret) {
+			dev_err(&pdev->dev, "Register hwrng failed: %d\n", ret);
+			qcom_rng_dev = NULL;
+			goto fail;
+		}
+	}
+
+	return ret;
+fail:
+	crypto_unregister_rng(&qcom_rng_alg);
+	return ret;
+}
+
+static void qcom_rng_remove(struct platform_device *pdev)
+{
+	crypto_unregister_rng(&qcom_rng_alg);
+
+	qcom_rng_dev = NULL;
+}
+
+static struct qcom_rng_match_data qcom_prng_match_data = {
+	.skip_init = false,
+	.hwrng_support = false,
+};
+
+static struct qcom_rng_match_data qcom_prng_ee_match_data = {
+	.skip_init = true,
+	.hwrng_support = false,
+};
+
+static struct qcom_rng_match_data qcom_trng_match_data = {
+	.skip_init = true,
+	.hwrng_support = true,
+};
+
+static const struct acpi_device_id __maybe_unused qcom_rng_acpi_match[] = {
+	{ .id = "QCOM8160", .driver_data = (kernel_ulong_t)&qcom_prng_ee_match_data },
+	{}
+};
+MODULE_DEVICE_TABLE(acpi, qcom_rng_acpi_match);
+
+static const struct of_device_id __maybe_unused qcom_rng_of_match[] = {
+	{ .compatible = "qcom,prng", .data = &qcom_prng_match_data },
+	{ .compatible = "qcom,prng-ee", .data = &qcom_prng_ee_match_data },
+	{ .compatible = "qcom,trng", .data = &qcom_trng_match_data },
+	{}
+};
+MODULE_DEVICE_TABLE(of, qcom_rng_of_match);
+
+static struct platform_driver qcom_rng_driver = {
+	.probe = qcom_rng_probe,
+	.remove =  qcom_rng_remove,
+	.driver = {
+		.name = KBUILD_MODNAME,
+		.of_match_table = qcom_rng_of_match,
+		.acpi_match_table = ACPI_PTR(qcom_rng_acpi_match),
+	}
+};
+module_platform_driver(qcom_rng_driver);
+
+MODULE_ALIAS("platform:" KBUILD_MODNAME);
+MODULE_DESCRIPTION("Qualcomm random number generator driver");
+MODULE_LICENSE("GPL v2");