thunderbolt: Fix NULL dereference in tb_remove_work()grafted

There is a slight race between tb_remove_work() and tb_domain_remove()
which leads to dereferencing a NULL tb->root_switch pointer inside
tb_free_unplugged_xdomains():

        Thread A                            Thread B

  tb_remove_work()
                                    tb_domain_remove()
                                      mutex_lock(&tb->lock)
                                      tb_stop()
                                        /* doesn't cancel a running callback */
                                        cancel_delayed_work(&tcm->remove_work)
                                        ...
                                        tb_switch_remove(tb->root_switch)
                                        tb->root_switch = NULL
                                      mutex_unlock(&tb->lock)
    mutex_lock(&tb->lock)
    ...
    /* without checking ->root_switch */
    tb_free_unplugged_xdomains(tb->root_switch)
    mutex_unlock(&tb->lock)

Commit a8937f35cf39 ("thunderbolt: Remove XDomain from the bus without
holding tb->lock") doesn't seem right to move tb_free_unplugged_xdomains()
out of the &tb->lock section and the check for tb->root_switch, in
particular.  It states:

  For this reason separate removing the XDomain from the topology data
  structures (where we need the lock) from unregistering the device from
  the bus (where remove callbacks of the drivers are being called).

tb_free_unplugged_xdomains() belongs to the former group of functions
requiring the lock.  And it also calls tb_xdomain_remove() which should
only be called with &tb->lock held.

Found by Linux Verification Center (linuxtesting.org) with Svace static
analysis tool.

Fixes: a8937f35cf39 ("thunderbolt: Remove XDomain from the bus without holding tb->lock")
Cc: stable@vger.kernel.org
Signed-off-by: Fedor Pchelkin <pchelkin@ispras.ru>
Signed-off-by: Mika Westerberg <mika.westerberg@linux.intel.com>

1 files changed, 155 insertions, 0 deletions

diff --git a/drivers/acpi/riscv/cppc.c b/drivers/acpi/riscv/cppc.c
new file mode 100644
index 000000000..42c1a9052
--- /dev/null
+++ b/drivers/acpi/riscv/cppc.c
@@ -0,0 +1,155 @@
+// SPDX-License-Identifier: GPL-2.0-only
+/*
+ * Implement CPPC FFH helper routines for RISC-V.
+ *
+ * Copyright (C) 2024 Ventana Micro Systems Inc.
+ */
+
+#include <acpi/cppc_acpi.h>
+#include <asm/csr.h>
+#include <asm/sbi.h>
+
+#define SBI_EXT_CPPC 0x43505043
+
+/* CPPC interfaces defined in SBI spec */
+#define SBI_CPPC_PROBE			0x0
+#define SBI_CPPC_READ			0x1
+#define SBI_CPPC_READ_HI		0x2
+#define SBI_CPPC_WRITE			0x3
+
+/* RISC-V FFH definitions from RISC-V FFH spec */
+#define FFH_CPPC_TYPE(r)		(((r) & GENMASK_ULL(63, 60)) >> 60)
+#define FFH_CPPC_SBI_REG(r)		((r) & GENMASK(31, 0))
+#define FFH_CPPC_CSR_NUM(r)		((r) & GENMASK(11, 0))
+
+#define FFH_CPPC_SBI			0x1
+#define FFH_CPPC_CSR			0x2
+
+struct sbi_cppc_data {
+	u64 val;
+	u32 reg;
+	struct sbiret ret;
+};
+
+static bool cppc_ext_present;
+
+static int __init sbi_cppc_init(void)
+{
+	if (sbi_spec_version >= sbi_mk_version(2, 0) &&
+	    sbi_probe_extension(SBI_EXT_CPPC) > 0) {
+		cppc_ext_present = true;
+	} else {
+		cppc_ext_present = false;
+	}
+
+	return 0;
+}
+device_initcall(sbi_cppc_init);
+
+static void sbi_cppc_read(void *read_data)
+{
+	struct sbi_cppc_data *data = (struct sbi_cppc_data *)read_data;
+
+	data->ret = sbi_ecall(SBI_EXT_CPPC, SBI_CPPC_READ,
+			      data->reg, 0, 0, 0, 0, 0);
+}
+
+static void sbi_cppc_write(void *write_data)
+{
+	struct sbi_cppc_data *data = (struct sbi_cppc_data *)write_data;
+
+	data->ret = sbi_ecall(SBI_EXT_CPPC, SBI_CPPC_WRITE,
+			      data->reg, data->val, 0, 0, 0, 0);
+}
+
+static void cppc_ffh_csr_read(void *read_data)
+{
+	struct sbi_cppc_data *data = (struct sbi_cppc_data *)read_data;
+
+	switch (data->reg) {
+	/* Support only TIME CSR for now */
+	case CSR_TIME:
+		data->ret.value = csr_read(CSR_TIME);
+		data->ret.error = 0;
+		break;
+	default:
+		data->ret.error = -EINVAL;
+		break;
+	}
+}
+
+static void cppc_ffh_csr_write(void *write_data)
+{
+	struct sbi_cppc_data *data = (struct sbi_cppc_data *)write_data;
+
+	data->ret.error = -EINVAL;
+}
+
+/*
+ * Refer to drivers/acpi/cppc_acpi.c for the description of the functions
+ * below.
+ */
+bool cpc_ffh_supported(void)
+{
+	return true;
+}
+
+int cpc_read_ffh(int cpu, struct cpc_reg *reg, u64 *val)
+{
+	struct sbi_cppc_data data;
+
+	if (WARN_ON_ONCE(irqs_disabled()))
+		return -EPERM;
+
+	if (FFH_CPPC_TYPE(reg->address) == FFH_CPPC_SBI) {
+		if (!cppc_ext_present)
+			return -EINVAL;
+
+		data.reg = FFH_CPPC_SBI_REG(reg->address);
+
+		smp_call_function_single(cpu, sbi_cppc_read, &data, 1);
+
+		*val = data.ret.value;
+
+		return (data.ret.error) ? sbi_err_map_linux_errno(data.ret.error) : 0;
+	} else if (FFH_CPPC_TYPE(reg->address) == FFH_CPPC_CSR) {
+		data.reg = FFH_CPPC_CSR_NUM(reg->address);
+
+		smp_call_function_single(cpu, cppc_ffh_csr_read, &data, 1);
+
+		*val = data.ret.value;
+
+		return data.ret.error;
+	}
+
+	return -EINVAL;
+}
+
+int cpc_write_ffh(int cpu, struct cpc_reg *reg, u64 val)
+{
+	struct sbi_cppc_data data;
+
+	if (WARN_ON_ONCE(irqs_disabled()))
+		return -EPERM;
+
+	if (FFH_CPPC_TYPE(reg->address) == FFH_CPPC_SBI) {
+		if (!cppc_ext_present)
+			return -EINVAL;
+
+		data.reg = FFH_CPPC_SBI_REG(reg->address);
+		data.val = val;
+
+		smp_call_function_single(cpu, sbi_cppc_write, &data, 1);
+
+		return (data.ret.error) ? sbi_err_map_linux_errno(data.ret.error) : 0;
+	} else if (FFH_CPPC_TYPE(reg->address) == FFH_CPPC_CSR) {
+		data.reg = FFH_CPPC_CSR_NUM(reg->address);
+		data.val = val;
+
+		smp_call_function_single(cpu, cppc_ffh_csr_write, &data, 1);
+
+		return data.ret.error;
+	}
+
+	return -EINVAL;
+}