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, 203 insertions, 0 deletions

diff --git a/tools/objtool/trace.c b/tools/objtool/trace.c
new file mode 100644
index 000000000..61c6aa302
--- /dev/null
+++ b/tools/objtool/trace.c
@@ -0,0 +1,203 @@
+// SPDX-License-Identifier: GPL-2.0-or-later
+/*
+ * Copyright (c) 2025, Oracle and/or its affiliates.
+ */
+
+#include <objtool/trace.h>
+
+bool trace;
+int trace_depth;
+
+/*
+ * Macros to trace CFI state attributes changes.
+ */
+
+#define TRACE_CFI_ATTR(attr, prev, next, fmt, ...)		\
+({								\
+	if ((prev)->attr != (next)->attr)			\
+		TRACE("%s=" fmt " ", #attr, __VA_ARGS__);	\
+})
+
+#define TRACE_CFI_ATTR_BOOL(attr, prev, next)			\
+	TRACE_CFI_ATTR(attr, prev, next,			\
+		       "%s", (next)->attr ? "true" : "false")
+
+#define TRACE_CFI_ATTR_NUM(attr, prev, next, fmt)		\
+	TRACE_CFI_ATTR(attr, prev, next, fmt, (next)->attr)
+
+#define CFI_REG_NAME_MAXLEN   16
+
+/*
+ * Return the name of a register. Note that the same static buffer
+ * is returned if the name is dynamically generated.
+ */
+static const char *cfi_reg_name(unsigned int reg)
+{
+	static char rname_buffer[CFI_REG_NAME_MAXLEN];
+	const char *rname;
+
+	switch (reg) {
+	case CFI_UNDEFINED:
+		return "<undefined>";
+	case CFI_CFA:
+		return "cfa";
+	case CFI_SP_INDIRECT:
+		return "(sp)";
+	case CFI_BP_INDIRECT:
+		return "(bp)";
+	}
+
+	if (reg < CFI_NUM_REGS) {
+		rname = arch_reg_name[reg];
+		if (rname)
+			return rname;
+	}
+
+	if (snprintf(rname_buffer, CFI_REG_NAME_MAXLEN, "r%d", reg) == -1)
+		return "<error>";
+
+	return (const char *)rname_buffer;
+}
+
+/*
+ * Functions and macros to trace CFI registers changes.
+ */
+
+static void trace_cfi_reg(const char *prefix, int reg, const char *fmt,
+			  int base_prev, int offset_prev,
+			  int base_next, int offset_next)
+{
+	char *rname;
+
+	if (base_prev == base_next && offset_prev == offset_next)
+		return;
+
+	if (prefix)
+		TRACE("%s:", prefix);
+
+	if (base_next == CFI_UNDEFINED) {
+		TRACE("%1$s=<undef> ", cfi_reg_name(reg));
+	} else {
+		rname = strdup(cfi_reg_name(reg));
+		TRACE(fmt, rname, cfi_reg_name(base_next), offset_next);
+		free(rname);
+	}
+}
+
+static void trace_cfi_reg_val(const char *prefix, int reg,
+			      int base_prev, int offset_prev,
+			      int base_next, int offset_next)
+{
+	trace_cfi_reg(prefix, reg, "%1$s=%2$s%3$+d ",
+		      base_prev, offset_prev, base_next, offset_next);
+}
+
+static void trace_cfi_reg_ref(const char *prefix, int reg,
+			      int base_prev, int offset_prev,
+			      int base_next, int offset_next)
+{
+	trace_cfi_reg(prefix, reg, "%1$s=(%2$s%3$+d) ",
+		      base_prev, offset_prev, base_next, offset_next);
+}
+
+#define TRACE_CFI_REG_VAL(reg, prev, next)				\
+	trace_cfi_reg_val(NULL, reg, prev.base, prev.offset,		\
+			  next.base, next.offset)
+
+#define TRACE_CFI_REG_REF(reg, prev, next)				\
+	trace_cfi_reg_ref(NULL, reg, prev.base, prev.offset,		\
+			  next.base, next.offset)
+
+void trace_insn_state(struct instruction *insn, struct insn_state *sprev,
+		      struct insn_state *snext)
+{
+	struct cfi_state *cprev, *cnext;
+	int i;
+
+	if (!memcmp(sprev, snext, sizeof(struct insn_state)))
+		return;
+
+	cprev = &sprev->cfi;
+	cnext = &snext->cfi;
+
+	disas_print_insn(stderr, objtool_disas_ctx, insn,
+			 trace_depth - 1, "state: ");
+
+	/* print registers changes */
+	TRACE_CFI_REG_VAL(CFI_CFA, cprev->cfa, cnext->cfa);
+	for (i = 0; i < CFI_NUM_REGS; i++) {
+		TRACE_CFI_REG_VAL(i, cprev->vals[i], cnext->vals[i]);
+		TRACE_CFI_REG_REF(i, cprev->regs[i], cnext->regs[i]);
+	}
+
+	/* print attributes changes */
+	TRACE_CFI_ATTR_NUM(stack_size, cprev, cnext, "%d");
+	TRACE_CFI_ATTR_BOOL(drap, cprev, cnext);
+	if (cnext->drap) {
+		trace_cfi_reg_val("drap", cnext->drap_reg,
+				  cprev->drap_reg, cprev->drap_offset,
+				  cnext->drap_reg, cnext->drap_offset);
+	}
+	TRACE_CFI_ATTR_BOOL(bp_scratch, cprev, cnext);
+	TRACE_CFI_ATTR_NUM(instr, sprev, snext, "%d");
+	TRACE_CFI_ATTR_NUM(uaccess_stack, sprev, snext, "%u");
+
+	TRACE("\n");
+
+	insn->trace = 1;
+}
+
+void trace_alt_begin(struct instruction *orig_insn, struct alternative *alt,
+		     char *alt_name)
+{
+	struct instruction *alt_insn;
+	char suffix[2];
+
+	alt_insn = alt->insn;
+
+	if (alt->type == ALT_TYPE_EX_TABLE) {
+		/*
+		 * When there is an exception table then the instruction
+		 * at the original location is executed but it can cause
+		 * an exception. In that case, the execution will be
+		 * redirected to the alternative instruction.
+		 *
+		 * The instruction at the original location can have
+		 * instruction alternatives, so we just print the location
+		 * of the instruction that can cause the exception and
+		 * not the instruction itself.
+		 */
+		TRACE_ALT_INFO_NOADDR(orig_insn, "/ ", "%s for instruction at 0x%lx <%s+0x%lx>",
+				      alt_name,
+				      orig_insn->offset, insn_sym(orig_insn)->name,
+				      orig_insn->offset - insn_sym(orig_insn)->offset);
+	} else {
+		TRACE_ALT_INFO_NOADDR(orig_insn, "/ ", "%s", alt_name);
+	}
+
+	if (alt->type == ALT_TYPE_JUMP_TABLE) {
+		/*
+		 * For a jump alternative, if the default instruction is
+		 * a NOP then it is replaced with the jmp instruction,
+		 * otherwise it is replaced with a NOP instruction.
+		 */
+		trace_depth++;
+		if (orig_insn->type == INSN_NOP) {
+			suffix[0] = (orig_insn->len == 5) ? 'q' : '\0';
+			TRACE_ADDR(orig_insn, "jmp%-3s %lx <%s+0x%lx>", suffix,
+				   alt_insn->offset, insn_sym(alt_insn)->name,
+				   alt_insn->offset - insn_sym(alt_insn)->offset);
+		} else {
+			TRACE_ADDR(orig_insn, "nop%d", orig_insn->len);
+			trace_depth--;
+		}
+	}
+}
+
+void trace_alt_end(struct instruction *orig_insn, struct alternative *alt,
+		   char *alt_name)
+{
+	if (alt->type == ALT_TYPE_JUMP_TABLE && orig_insn->type == INSN_NOP)
+		trace_depth--;
+	TRACE_ALT_INFO_NOADDR(orig_insn, "\\ ", "%s", alt_name);
+}