objtool: Support pv_opsindirect calls for noinstr

Normally objtool will now follow indirect calls; there is no need.

However, this becomes a problem with noinstr validation; if there's an
indirect call from noinstr code, we very much need to know it is to
another noinstr function. Luckily there aren't many indirect calls in
entry code with the obvious exception of paravirt. As such, noinstr
validation didn't work with paravirt kernels.

In order to track pv_ops[] call targets, objtool reads the static
pv_ops[] tables as well as direct assignments to the pv_ops[] array,
provided the compiler makes them a single instruction like:

  bf87:       48 c7 05 00 00 00 00 00 00 00 00        movq   $0x0,0x0(%rip)
    bf92 <xen_init_spinlocks+0x5f>
    bf8a: R_X86_64_PC32     pv_ops+0x268

There are, as of yet, no warnings for when this goes wrong :/

Using the functions found with the above means, all pv_ops[] calls are
now subject to noinstr validation.

Signed-off-by: Peter Zijlstra (Intel) <peterz@infradead.org>
Link: https://lore.kernel.org/r/20210624095149.118815755@infradead.org

1 files changed, 141 insertions, 10 deletions

diff --git a/tools/objtool/check.c b/tools/objtool/check.c
index c6f206fee8ff..84e59a97bab6 100644
--- a/tools/objtool/check.c
+++ b/tools/objtool/check.c
@@ -382,7 +382,7 @@ static int decode_instructions(struct objtool_file *file)
 			insn->sec = sec;
 			insn->offset = offset;
 
-			ret = arch_decode_instruction(file->elf, sec, offset,
+			ret = arch_decode_instruction(file, sec, offset,
 						      sec->len - offset,
 						      &insn->len, &insn->type,
 						      &insn->immediate,
@@ -420,6 +420,82 @@ err:
 	return ret;
 }
 
+/*
+ * Read the pv_ops[] .data table to find the static initialized values.
+ */
+static int add_pv_ops(struct objtool_file *file, const char *symname)
+{
+	struct symbol *sym, *func;
+	unsigned long off, end;
+	struct reloc *rel;
+	int idx;
+
+	sym = find_symbol_by_name(file->elf, symname);
+	if (!sym)
+		return 0;
+
+	off = sym->offset;
+	end = off + sym->len;
+	for (;;) {
+		rel = find_reloc_by_dest_range(file->elf, sym->sec, off, end - off);
+		if (!rel)
+			break;
+
+		func = rel->sym;
+		if (func->type == STT_SECTION)
+			func = find_symbol_by_offset(rel->sym->sec, rel->addend);
+
+		idx = (rel->offset - sym->offset) / sizeof(unsigned long);
+
+		objtool_pv_add(file, idx, func);
+
+		off = rel->offset + 1;
+		if (off > end)
+			break;
+	}
+
+	return 0;
+}
+
+/*
+ * Allocate and initialize file->pv_ops[].
+ */
+static int init_pv_ops(struct objtool_file *file)
+{
+	static const char *pv_ops_tables[] = {
+		"pv_ops",
+		"xen_cpu_ops",
+		"xen_irq_ops",
+		"xen_mmu_ops",
+		NULL,
+	};
+	const char *pv_ops;
+	struct symbol *sym;
+	int idx, nr;
+
+	if (!noinstr)
+		return 0;
+
+	file->pv_ops = NULL;
+
+	sym = find_symbol_by_name(file->elf, "pv_ops");
+	if (!sym)
+		return 0;
+
+	nr = sym->len / sizeof(unsigned long);
+	file->pv_ops = calloc(sizeof(struct pv_state), nr);
+	if (!file->pv_ops)
+		return -1;
+
+	for (idx = 0; idx < nr; idx++)
+		INIT_LIST_HEAD(&file->pv_ops[idx].targets);
+
+	for (idx = 0; (pv_ops = pv_ops_tables[idx]); idx++)
+		add_pv_ops(file, pv_ops);
+
+	return 0;
+}
+
 static struct instruction *find_last_insn(struct objtool_file *file,
 					  struct section *sec)
 {
@@ -893,6 +969,9 @@ static struct reloc *insn_reloc(struct objtool_file *file, struct instruction *i
 		return NULL;
 
 	if (!insn->reloc) {
+		if (!file)
+			return NULL;
+
 		insn->reloc = find_reloc_by_dest_range(file->elf, insn->sec,
 						       insn->offset, insn->len);
 		if (!insn->reloc) {
@@ -1882,6 +1961,10 @@ static int decode_sections(struct objtool_file *file)
 
 	mark_rodata(file);
 
+	ret = init_pv_ops(file);
+	if (ret)
+		return ret;
+
 	ret = decode_instructions(file);
 	if (ret)
 		return ret;
@@ -2663,20 +2746,64 @@ static inline bool func_uaccess_safe(struct symbol *func)
 
 static inline const char *call_dest_name(struct instruction *insn)
 {
+	static char pvname[16];
+	struct reloc *rel;
+	int idx;
+
 	if (insn->call_dest)
 		return insn->call_dest->name;
 
+	rel = insn_reloc(NULL, insn);
+	if (rel && !strcmp(rel->sym->name, "pv_ops")) {
+		idx = (rel->addend / sizeof(void *));
+		snprintf(pvname, sizeof(pvname), "pv_ops[%d]", idx);
+		return pvname;
+	}
+
 	return "{dynamic}";
 }
 
-static inline bool noinstr_call_dest(struct symbol *func)
+static bool pv_call_dest(struct objtool_file *file, struct instruction *insn)
+{
+	struct symbol *target;
+	struct reloc *rel;
+	int idx;
+
+	rel = insn_reloc(file, insn);
+	if (!rel || strcmp(rel->sym->name, "pv_ops"))
+		return false;
+
+	idx = (arch_dest_reloc_offset(rel->addend) / sizeof(void *));
+
+	if (file->pv_ops[idx].clean)
+		return true;
+
+	file->pv_ops[idx].clean = true;
+
+	list_for_each_entry(target, &file->pv_ops[idx].targets, pv_target) {
+		if (!target->sec->noinstr) {
+			WARN("pv_ops[%d]: %s", idx, target->name);
+			file->pv_ops[idx].clean = false;
+		}
+	}
+
+	return file->pv_ops[idx].clean;
+}
+
+static inline bool noinstr_call_dest(struct objtool_file *file,
+				     struct instruction *insn,
+				     struct symbol *func)
 {
 	/*
 	 * We can't deal with indirect function calls at present;
 	 * assume they're instrumented.
 	 */
-	if (!func)
+	if (!func) {
+		if (file->pv_ops)
+			return pv_call_dest(file, insn);
+
 		return false;
+	}
 
 	/*
 	 * If the symbol is from a noinstr section; we good.
@@ -2695,10 +2822,12 @@ static inline bool noinstr_call_dest(struct symbol *func)
 	return false;
 }
 
-static int validate_call(struct instruction *insn, struct insn_state *state)
+static int validate_call(struct objtool_file *file,
+			 struct instruction *insn,
+			 struct insn_state *state)
 {
 	if (state->noinstr && state->instr <= 0 &&
-	    !noinstr_call_dest(insn->call_dest)) {
+	    !noinstr_call_dest(file, insn, insn->call_dest)) {
 		WARN_FUNC("call to %s() leaves .noinstr.text section",
 				insn->sec, insn->offset, call_dest_name(insn));
 		return 1;
@@ -2719,7 +2848,9 @@ static int validate_call(struct instruction *insn, struct insn_state *state)
 	return 0;
 }
 
-static int validate_sibling_call(struct instruction *insn, struct insn_state *state)
+static int validate_sibling_call(struct objtool_file *file,
+				 struct instruction *insn,
+				 struct insn_state *state)
 {
 	if (has_modified_stack_frame(insn, state)) {
 		WARN_FUNC("sibling call from callable instruction with modified stack frame",
@@ -2727,7 +2858,7 @@ static int validate_sibling_call(struct instruction *insn, struct insn_state *st
 		return 1;
 	}
 
-	return validate_call(insn, state);
+	return validate_call(file, insn, state);
 }
 
 static int validate_return(struct symbol *func, struct instruction *insn, struct insn_state *state)
@@ -2880,7 +3011,7 @@ static int validate_branch(struct objtool_file *file, struct symbol *func,
 
 		case INSN_CALL:
 		case INSN_CALL_DYNAMIC:
-			ret = validate_call(insn, &state);
+			ret = validate_call(file, insn, &state);
 			if (ret)
 				return ret;
 
@@ -2899,7 +3030,7 @@ static int validate_branch(struct objtool_file *file, struct symbol *func,
 		case INSN_JUMP_CONDITIONAL:
 		case INSN_JUMP_UNCONDITIONAL:
 			if (is_sibling_call(insn)) {
-				ret = validate_sibling_call(insn, &state);
+				ret = validate_sibling_call(file, insn, &state);
 				if (ret)
 					return ret;
 
@@ -2921,7 +3052,7 @@ static int validate_branch(struct objtool_file *file, struct symbol *func,
 		case INSN_JUMP_DYNAMIC:
 		case INSN_JUMP_DYNAMIC_CONDITIONAL:
 			if (is_sibling_call(insn)) {
-				ret = validate_sibling_call(insn, &state);
+				ret = validate_sibling_call(file, insn, &state);
 				if (ret)
 					return ret;
 			}