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, 232 insertions, 0 deletions

diff --git a/drivers/nvmem/sunxi_sid.c b/drivers/nvmem/sunxi_sid.c
new file mode 100644
index 000000000..ba14a7620
--- /dev/null
+++ b/drivers/nvmem/sunxi_sid.c
@@ -0,0 +1,232 @@
+// SPDX-License-Identifier: GPL-2.0+
+/*
+ * Allwinner sunXi SoCs Security ID support.
+ *
+ * Copyright (c) 2013 Oliver Schinagl <oliver@schinagl.nl>
+ * Copyright (C) 2014 Maxime Ripard <maxime.ripard@free-electrons.com>
+ */
+
+#include <linux/device.h>
+#include <linux/io.h>
+#include <linux/iopoll.h>
+#include <linux/module.h>
+#include <linux/nvmem-provider.h>
+#include <linux/of.h>
+#include <linux/platform_device.h>
+#include <linux/slab.h>
+#include <linux/random.h>
+
+/* Registers and special values for doing register-based SID readout on H3 */
+#define SUN8I_SID_PRCTL		0x40
+#define SUN8I_SID_RDKEY		0x60
+
+#define SUN8I_SID_OFFSET_MASK	0x1FF
+#define SUN8I_SID_OFFSET_SHIFT	16
+#define SUN8I_SID_OP_LOCK	(0xAC << 8)
+#define SUN8I_SID_READ		BIT(1)
+
+struct sunxi_sid_cfg {
+	u32	value_offset;
+	u32	size;
+	bool	need_register_readout;
+};
+
+struct sunxi_sid {
+	void __iomem		*base;
+	u32			value_offset;
+};
+
+static int sunxi_sid_read(void *context, unsigned int offset,
+			  void *val, size_t bytes)
+{
+	struct sunxi_sid *sid = context;
+	u32 word;
+
+	/* .stride = 4 so offset is guaranteed to be aligned */
+	__ioread32_copy(val, sid->base + sid->value_offset + offset, bytes / 4);
+
+	val += round_down(bytes, 4);
+	offset += round_down(bytes, 4);
+	bytes = bytes % 4;
+
+	if (!bytes)
+		return 0;
+
+	/* Handle any trailing bytes */
+	word = readl_relaxed(sid->base + sid->value_offset + offset);
+	memcpy(val, &word, bytes);
+
+	return 0;
+}
+
+static int sun8i_sid_register_readout(const struct sunxi_sid *sid,
+				      const unsigned int offset,
+				      u32 *out)
+{
+	u32 reg_val;
+	int ret;
+
+	/* Set word, lock access, and set read command */
+	reg_val = (offset & SUN8I_SID_OFFSET_MASK)
+		  << SUN8I_SID_OFFSET_SHIFT;
+	reg_val |= SUN8I_SID_OP_LOCK | SUN8I_SID_READ;
+	writel(reg_val, sid->base + SUN8I_SID_PRCTL);
+
+	ret = readl_poll_timeout(sid->base + SUN8I_SID_PRCTL, reg_val,
+				 !(reg_val & SUN8I_SID_READ), 100, 250000);
+	if (ret)
+		return ret;
+
+	if (out)
+		*out = readl(sid->base + SUN8I_SID_RDKEY);
+
+	writel(0, sid->base + SUN8I_SID_PRCTL);
+
+	return 0;
+}
+
+/*
+ * On Allwinner H3, the value on the 0x200 offset of the SID controller seems
+ * to be not reliable at all.
+ * Read by the registers instead.
+ */
+static int sun8i_sid_read_by_reg(void *context, unsigned int offset,
+				 void *val, size_t bytes)
+{
+	struct sunxi_sid *sid = context;
+	u32 word;
+	int ret;
+
+	/* .stride = 4 so offset is guaranteed to be aligned */
+	while (bytes >= 4) {
+		ret = sun8i_sid_register_readout(sid, offset, val);
+		if (ret)
+			return ret;
+
+		val += 4;
+		offset += 4;
+		bytes -= 4;
+	}
+
+	if (!bytes)
+		return 0;
+
+	/* Handle any trailing bytes */
+	ret = sun8i_sid_register_readout(sid, offset, &word);
+	if (ret)
+		return ret;
+
+	memcpy(val, &word, bytes);
+
+	return 0;
+}
+
+static int sunxi_sid_probe(struct platform_device *pdev)
+{
+	struct device *dev = &pdev->dev;
+	struct nvmem_config *nvmem_cfg;
+	struct nvmem_device *nvmem;
+	struct sunxi_sid *sid;
+	int size;
+	char *randomness;
+	const struct sunxi_sid_cfg *cfg;
+
+	sid = devm_kzalloc(dev, sizeof(*sid), GFP_KERNEL);
+	if (!sid)
+		return -ENOMEM;
+
+	cfg = of_device_get_match_data(dev);
+	if (!cfg)
+		return -EINVAL;
+	sid->value_offset = cfg->value_offset;
+
+	sid->base = devm_platform_ioremap_resource(pdev, 0);
+	if (IS_ERR(sid->base))
+		return PTR_ERR(sid->base);
+
+	size = cfg->size;
+
+	nvmem_cfg = devm_kzalloc(dev, sizeof(*nvmem_cfg), GFP_KERNEL);
+	if (!nvmem_cfg)
+		return -ENOMEM;
+
+	nvmem_cfg->dev = dev;
+	nvmem_cfg->name = "sunxi-sid";
+	nvmem_cfg->type = NVMEM_TYPE_OTP;
+	nvmem_cfg->add_legacy_fixed_of_cells = true;
+	nvmem_cfg->read_only = true;
+	nvmem_cfg->size = cfg->size;
+	nvmem_cfg->word_size = 1;
+	nvmem_cfg->stride = 4;
+	nvmem_cfg->priv = sid;
+	if (cfg->need_register_readout)
+		nvmem_cfg->reg_read = sun8i_sid_read_by_reg;
+	else
+		nvmem_cfg->reg_read = sunxi_sid_read;
+
+	nvmem = devm_nvmem_register(dev, nvmem_cfg);
+	if (IS_ERR(nvmem))
+		return PTR_ERR(nvmem);
+
+	randomness = kzalloc(size, GFP_KERNEL);
+	if (!randomness)
+		return -ENOMEM;
+
+	nvmem_cfg->reg_read(sid, 0, randomness, size);
+	add_device_randomness(randomness, size);
+	kfree(randomness);
+
+	platform_set_drvdata(pdev, nvmem);
+
+	return 0;
+}
+
+static const struct sunxi_sid_cfg sun4i_a10_cfg = {
+	.size = 0x10,
+};
+
+static const struct sunxi_sid_cfg sun7i_a20_cfg = {
+	.size = 0x200,
+};
+
+static const struct sunxi_sid_cfg sun8i_h3_cfg = {
+	.value_offset = 0x200,
+	.size = 0x100,
+	.need_register_readout = true,
+};
+
+static const struct sunxi_sid_cfg sun50i_a64_cfg = {
+	.value_offset = 0x200,
+	.size = 0x100,
+};
+
+static const struct sunxi_sid_cfg sun50i_h6_cfg = {
+	.value_offset = 0x200,
+	.size = 0x200,
+};
+
+static const struct of_device_id sunxi_sid_of_match[] = {
+	{ .compatible = "allwinner,sun4i-a10-sid", .data = &sun4i_a10_cfg },
+	{ .compatible = "allwinner,sun7i-a20-sid", .data = &sun7i_a20_cfg },
+	{ .compatible = "allwinner,sun8i-a83t-sid", .data = &sun50i_a64_cfg },
+	{ .compatible = "allwinner,sun8i-h3-sid", .data = &sun8i_h3_cfg },
+	{ .compatible = "allwinner,sun20i-d1-sid", .data = &sun50i_a64_cfg },
+	{ .compatible = "allwinner,sun50i-a64-sid", .data = &sun50i_a64_cfg },
+	{ .compatible = "allwinner,sun50i-h5-sid", .data = &sun50i_a64_cfg },
+	{ .compatible = "allwinner,sun50i-h6-sid", .data = &sun50i_h6_cfg },
+	{/* sentinel */},
+};
+MODULE_DEVICE_TABLE(of, sunxi_sid_of_match);
+
+static struct platform_driver sunxi_sid_driver = {
+	.probe = sunxi_sid_probe,
+	.driver = {
+		.name = "eeprom-sunxi-sid",
+		.of_match_table = sunxi_sid_of_match,
+	},
+};
+module_platform_driver(sunxi_sid_driver);
+
+MODULE_AUTHOR("Oliver Schinagl <oliver@schinagl.nl>");
+MODULE_DESCRIPTION("Allwinner sunxi security id driver");
+MODULE_LICENSE("GPL");