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Date: Thu, 16 Apr 2020 17:07:56 +0200
From: Peter Zijlstra <peterz@...radead.org>
To: jpoimboe@...hat.com, alexandre.chartre@...cle.com
Cc: linux-kernel@...r.kernel.org, jthierry@...hat.com,
tglx@...utronix.de, x86@...nel.org, peterz@...radead.org
Subject: [RFC][PATCH 4/7] objtool: Add support for intra-function calls
From: Alexandre Chartre <alexandre.chartre@...cle.com>
Change objtool to support intra-function calls. On x86, an intra-function
call is represented in objtool as a push onto the stack (of the return
address), and a jump to the destination address. That way the stack
information is correctly updated and the call flow is still accurate.
Signed-off-by: Alexandre Chartre <alexandre.chartre@...cle.com>
Signed-off-by: Peter Zijlstra (Intel) <peterz@...radead.org>
Link: https://lkml.kernel.org/r/20200414103618.12657-4-alexandre.chartre@oracle.com
---
include/linux/frame.h | 11 +
tools/objtool/Documentation/stack-validation.txt | 8 +
tools/objtool/arch/x86/decode.c | 17 ++-
tools/objtool/check.c | 129 ++++++++++++++++++-----
tools/objtool/check.h | 1
5 files changed, 140 insertions(+), 26 deletions(-)
--- a/include/linux/frame.h
+++ b/include/linux/frame.h
@@ -15,9 +15,20 @@
static void __used __section(.discard.func_stack_frame_non_standard) \
*__func_stack_frame_non_standard_##func = func
+/*
+ * This macro indicates that the following intra-function call is valid.
+ * Any non-annotated intra-function call will cause objtool to issue warning.
+ */
+#define ANNOTATE_INTRA_FUNCTION_CALL \
+ 999: \
+ .pushsection .discard.intra_function_calls; \
+ .long 999b; \
+ .popsection;
+
#else /* !CONFIG_STACK_VALIDATION */
#define STACK_FRAME_NON_STANDARD(func)
+#define ANNOTATE_INTRA_FUNCTION_CALL
#endif /* CONFIG_STACK_VALIDATION */
--- a/tools/objtool/Documentation/stack-validation.txt
+++ b/tools/objtool/Documentation/stack-validation.txt
@@ -290,6 +290,14 @@ they mean, and suggestions for how to fi
https://gcc.gnu.org/bugzilla/show_bug.cgi?id=70646
+9. file.o: warning: unsupported intra-function call
+
+ This warning means that a direct call is done to a destination which
+ is not at the beginning of a function. If this is a legit call, you
+ can remove this warning by putting the ANNOTATE_INTRA_FUNCTION_CALL
+ directive right before the call.
+
+
If the error doesn't seem to make sense, it could be a bug in objtool.
Feel free to ask the objtool maintainer for help.
--- a/tools/objtool/arch/x86/decode.c
+++ b/tools/objtool/arch/x86/decode.c
@@ -453,6 +453,12 @@ int arch_decode_instruction(struct elf *
case 0xe8:
*type = INSN_CALL;
+ /*
+ * For the impact on the stack, a call behaves like
+ * a push of an immediate value (the return address).
+ */
+ op->src.type = OP_SRC_CONST;
+ op->dest.type = OP_DEST_PUSH;
break;
case 0xfc:
@@ -493,10 +499,17 @@ int arch_decode_instruction(struct elf *
*immediate = insn.immediate.nbytes ? insn.immediate.value : 0;
- if (*type == INSN_STACK || *type == INSN_EXCEPTION_RETURN)
+ switch (*type) {
+ case INSN_STACK:
+ case INSN_EXCEPTION_RETURN:
+ case INSN_CALL:
list_add_tail(&op->list, ops_list);
- else
+ break;
+
+ default:
free(op);
+ break;
+ }
return 0;
}
--- a/tools/objtool/check.c
+++ b/tools/objtool/check.c
@@ -691,44 +691,51 @@ static int add_jump_destinations(struct
return 0;
}
+static int setup_call_dest(struct objtool_file *file, struct instruction *insn)
+{
+ unsigned long dest_off;
+
+ dest_off = insn->offset + insn->len + insn->immediate;
+ insn->call_dest = find_func_by_offset(insn->sec, dest_off);
+ if (!insn->call_dest)
+ insn->call_dest = find_symbol_by_offset(insn->sec, dest_off);
+
+ if (!insn->call_dest) {
+ /* intra-function call */
+ if (insn->intra_function_call)
+ return 0;
+
+ WARN_FUNC("intra-function call", insn->sec, insn->offset);
+ return -1;
+ }
+
+ /* regular call */
+ if (insn->func && insn->call_dest->type != STT_FUNC) {
+ WARN_FUNC("unsupported call to non-function",
+ insn->sec, insn->offset);
+ return -1;
+ }
+
+ return 0;
+}
+
/*
* Find the destination instructions for all calls.
*/
static int add_call_destinations(struct objtool_file *file)
{
struct instruction *insn;
- unsigned long dest_off;
struct rela *rela;
for_each_insn(file, insn) {
- if (insn->type != INSN_CALL)
+ if (insn->type != INSN_CALL || insn->ignore)
continue;
rela = find_rela_by_dest_range(file->elf, insn->sec,
insn->offset, insn->len);
if (!rela) {
- dest_off = insn->offset + insn->len + insn->immediate;
- insn->call_dest = find_func_by_offset(insn->sec, dest_off);
- if (!insn->call_dest)
- insn->call_dest = find_symbol_by_offset(insn->sec, dest_off);
-
- if (insn->ignore)
- continue;
-
- if (!insn->call_dest) {
- WARN_FUNC("unsupported intra-function call",
- insn->sec, insn->offset);
- if (retpoline)
- WARN("If this is a retpoline, please patch it in with alternatives and annotate it with ANNOTATE_NOSPEC_ALTERNATIVE.");
- return -1;
- }
-
- if (insn->func && insn->call_dest->type != STT_FUNC) {
- WARN_FUNC("unsupported call to non-function",
- insn->sec, insn->offset);
+ if (setup_call_dest(file, insn))
return -1;
- }
-
} else if (rela->sym->type == STT_SECTION) {
insn->call_dest = find_func_by_offset(rela->sym->sec,
rela->addend+4);
@@ -1414,6 +1421,52 @@ static int read_instr_hints(struct objto
return 0;
}
+static int read_intra_function_calls(struct objtool_file *file)
+{
+ struct instruction *insn;
+ struct section *sec;
+ struct rela *rela;
+
+ sec = find_section_by_name(file->elf, ".rela.discard.intra_function_calls");
+ if (!sec)
+ return 0;
+
+ list_for_each_entry(rela, &sec->rela_list, list) {
+ unsigned long dest_off;
+
+ if (rela->sym->type != STT_SECTION) {
+ WARN("unexpected relocation symbol type in %s",
+ sec->name);
+ return -1;
+ }
+
+ insn = find_insn(file, rela->sym->sec, rela->addend);
+ if (!insn) {
+ WARN("bad .discard.intra_function_call entry");
+ return -1;
+ }
+
+ if (insn->type != INSN_CALL) {
+ WARN_FUNC("intra_function_call not a direct call",
+ insn->sec, insn->offset);
+ return -1;
+ }
+
+ insn->intra_function_call = true;
+
+ dest_off = insn->offset + insn->len + insn->immediate;
+ insn->jump_dest = find_insn(file, insn->sec, dest_off);
+ if (!insn->jump_dest) {
+ WARN_FUNC("can't find call dest at %s+0x%lx",
+ insn->sec, insn->offset,
+ insn->sec->name, dest_off);
+ return -1;
+ }
+ }
+
+ return 0;
+}
+
static void mark_rodata(struct objtool_file *file)
{
struct section *sec;
@@ -1469,6 +1522,10 @@ static int decode_sections(struct objtoo
if (ret)
return ret;
+ ret = read_intra_function_calls(file);
+ if (ret)
+ return ret;
+
ret = add_call_destinations(file);
if (ret)
return ret;
@@ -2260,7 +2317,8 @@ static int validate_branch(struct objtoo
return ret;
if (!no_fp && func && !is_fentry_call(insn) &&
- !has_valid_stack_frame(&state)) {
+ !has_valid_stack_frame(&state) &&
+ !insn->intra_function_call) {
WARN_FUNC("call without frame pointer save/setup",
sec, insn->offset);
return 1;
@@ -2269,6 +2327,29 @@ static int validate_branch(struct objtoo
if (dead_end_function(file, insn->call_dest))
return 0;
+ if (insn->intra_function_call) {
+ /*
+ * The call instruction can update the stack
+ * state. Then make the intra-function call
+ * behaves like and unconditional jump.
+ */
+ ret = handle_insn_ops(insn, &state);
+ if (ret)
+ return ret;
+
+ ret = validate_branch(file, func, insn,
+ insn->jump_dest, state);
+ if (ret) {
+ if (backtrace) {
+ BT_FUNC("(intra-function call)",
+ insn);
+ }
+ return ret;
+ }
+
+ return 0;
+ }
+
break;
case INSN_JUMP_CONDITIONAL:
--- a/tools/objtool/check.h
+++ b/tools/objtool/check.h
@@ -33,6 +33,7 @@ struct instruction {
int alt_group;
bool dead_end, ignore, ignore_alts;
bool hint;
+ bool intra_function_call;
bool retpoline_safe;
s8 instr;
u8 visited;
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