Patch "objtool: Allow alternatives to be ignored" has been added to the 4.9-stable tree

This is a note to let you know that I've just added the patch titled

objtool: Allow alternatives to be ignored

to the 4.9-stable tree which can be found at:
http://www.kernel.org/git/?p=linux/kernel/git/stable/stable-queue.git;a=summary

The filename of the patch is:
objtool-allow-alternatives-to-be-ignored.patch
and it can be found in the queue-4.9 subdirectory.

If you, or anyone else, feels it should not be added to the stable tree, please let <[email protected]> know about it.

From: Josh Poimboeuf <[email protected]>
Date: Thu, 11 Jan 2018 21:46:24 +0000
Subject: objtool: Allow alternatives to be ignored

From: Josh Poimboeuf <[email protected]>

commit 258c76059cece01bebae098e81bacb1af2edad17 upstream.

Getting objtool to understand retpolines is going to be a bit of a challenge. For now, take advantage of the fact that retpolines are patched in with alternatives. Just read the original (sane) non-alternative instruction, and ignore the patched-in retpoline.

This allows objtool to understand the control flow *around* the retpoline, even if it can't yet follow what's inside. This means the ORC unwinder will fail to unwind from inside a retpoline, but will work fine otherwise.

---
 tools/objtool/builtin-check.c |   64 +++++++++++++++++++++++++++++++++++++-----
 1 file changed, 57 insertions(+), 7 deletions(-)

@@ -51,7 +51,7 @@ struct instruction {
 	unsigned int len, state;
 	unsigned char type;
 	unsigned long immediate;
-	bool alt_group, visited;
+	bool alt_group, visited, ignore_alts;
 	struct symbol *call_dest;
 	struct instruction *jump_dest;
 	struct list_head alts;

@@ -353,6 +353,40 @@ static void add_ignores(struct objtool_f
 }
 
 /*
+ * FIXME: For now, just ignore any alternatives which add retpolines.  This is
+ * a temporary hack, as it doesn't allow ORC to unwind from inside a retpoline.
+ * But it at least allows objtool to understand the control flow *around* the
+ * retpoline.
+ */
+static int add_nospec_ignores(struct objtool_file *file)
+{
+	struct section *sec;
+	struct rela *rela;
+	struct instruction *insn;
+
+	sec = find_section_by_name(file->elf, ".rela.discard.nospec");
+	if (!sec)
+		return 0;
+
+	list_for_each_entry(rela, &sec->rela_list, list) {
+		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.nospec entry");
+			return -1;
+		}
+
+		insn->ignore_alts = true;
+	}
+
+	return 0;
+}
+
+/*
  * Find the destination instructions for all jumps.
  */
 static int add_jump_destinations(struct objtool_file *file)

@@ -435,11 +469,18 @@ static int add_call_destinations(struct
 			dest_off = insn->offset + insn->len + insn->immediate;
 			insn->call_dest = find_symbol_by_offset(insn->sec,
 								dest_off);
+			/*
+			 * FIXME: Thanks to retpolines, it's now considered
+			 * normal for a function to call within itself.  So
+			 * disable this warning for now.
+			 */
+#if 0
 			if (!insn->call_dest) {
 				WARN_FUNC("can't find call dest symbol at offset 0x%lx",
 					  insn->sec, insn->offset, dest_off);
 				return -1;
 			}
+#endif
 		} else if (rela->sym->type == STT_SECTION) {
 			insn->call_dest = find_symbol_by_offset(rela->sym->sec,
 								rela->addend+4);

@@ -601,12 +642,6 @@ static int add_special_section_alts(stru
 		return ret;
 
 	list_for_each_entry_safe(special_alt, tmp, &special_alts, list) {
-		alt = malloc(sizeof(*alt));
-		if (!alt) {
-			WARN("malloc failed");
-			ret = -1;
-			goto out;
-		}
 
 		orig_insn = find_insn(file, special_alt->orig_sec,
 				      special_alt->orig_off);

@@ -617,6 +652,10 @@ static int add_special_section_alts(stru
 			goto out;
 		}
 
+		/* Ignore retpoline alternatives. */
+		if (orig_insn->ignore_alts)
+			continue;
+
 		new_insn = NULL;
 		if (!special_alt->group || special_alt->new_len) {
 			new_insn = find_insn(file, special_alt->new_sec,

@@ -642,6 +681,13 @@ static int add_special_section_alts(stru
 				goto out;
 		}
 
+		alt = malloc(sizeof(*alt));
+		if (!alt) {
+			WARN("malloc failed");
+			ret = -1;
+			goto out;
+		}
+
 		alt->insn = new_insn;
 		list_add_tail(&alt->list, &orig_insn->alts);
 

@@ -861,6 +907,10 @@ static int decode_sections(struct objtoo
 
 	add_ignores(file);
 
+	ret = add_nospec_ignores(file);
+	if (ret)
+		return ret;
+
 	ret = add_jump_destinations(file);
 	if (ret)
 		return ret;

Patches currently in stable-queue which might be from [email protected] are

queue-4.9/x86-spectre-add-boot-time-option-to-select-spectre-v2-mitigation.patch queue-4.9/x86-retpoline-irq32-convert-assembler-indirect-jumps.patch queue-4.9/objtool-detect-jumps-to-retpoline-thunks.patch queue-4.9/x86-retpoline-hyperv-convert-assembler-indirect-jumps.patch queue-4.9/x86-retpoline-entry-convert-entry-assembler-indirect-jumps.patch queue-4.9/x86-asm-use-register-variable-to-get-stack-pointer-value.patch queue-4.9/x86-cpufeatures-add-x86_bug_cpu_insecure.patch queue-4.9/objtool-modules-discard-objtool-annotation-sections-for-modules.patch queue-4.9/x86-cpufeatures-make-cpu-bugs-sticky.patch queue-4.9/x86-retpoline-ftrace-convert-ftrace-assembler-indirect-jumps.patch queue-4.9/objtool-allow-alternatives-to-be-ignored.patch queue-4.9/x86-retpoline-crypto-convert-crypto-assembler-indirect-jumps.patch queue-4.9/selftests-x86-add-test_vsyscall.patch queue-4.9/x86-retpoline-xen-convert-xen-hypercall-indirect-jumps.patch queue-4.9/x86-cpu-merge-bugs.c-and-bugs_64.c.patch queue-4.9/x86-retpoline-checksum32-convert-assembler-indirect-jumps.patch queue-4.9/x86-retpoline-fill-return-stack-buffer-on-vmexit.patch queue-4.9/x86-retpoline-remove-compile-time-warning.patch queue-4.9/x86-retpoline-add-initial-retpoline-support.patch

Hm... they aren't being ignored entirely.

arch/x86/crypto/camellia-aesni-avx2-asm_64.o: warning: objtool: .altinstr_replacement+0xf: return instruction outside of a callable function

Josh?

This should fix it (to be applied on top):

----

From: Josh Poimboeuf <[email protected]>
Subject: [PATCH] objtool: Fix retpoline support for pre-ORC objtool

Objtool 1.0 (pre-ORC) produces the following warning when it encounters a retpoline:

arch/x86/crypto/camellia-aesni-avx2-asm_64.o: warning: objtool: .altinstr_replacement+0xf: return instruction outside of a callable function

That warning is meant to catch GCC bugs and missing ENTRY/ENDPROC annotations, neither of which are applicable to alternatives. Silence the warning for alternative instructions, just like objtool 2.0 already does.

---
 tools/objtool/builtin-check.c | 8 ++++++++
 1 file changed, 8 insertions(+)

index f789621cbdba..a688a857a7ae 100644
@@ -1230,6 +1230,14 @@ static int validate_uncallable_instructions(struct objtool_file *file)
 
 	for_each_insn(file, insn) {
 		if (!insn->visited && insn->type == INSN_RETURN) {
+
+			/*
+			 * Don't warn about call instructions in unvisited
+			 * retpoline alternatives.
+			 */
+			if (!strcmp(insn->sec->name, ".altinstr_replacement"))
+				continue;
+
 			WARN_FUNC("return instruction outside of a callable function",
 				  insn->sec, insn->offset);
 			warnings++;

2.14.3

This is a note to let you know that I've just added the patch titled

objtool: Fix retpoline support for pre-ORC objtool

to the 4.9-stable tree which can be found at:
http://www.kernel.org/git/?p=linux/kernel/git/stable/stable-queue.git;a=summary

The filename of the patch is:
objtool-fix-retpoline-support-for-pre-orc-objtool.patch
and it can be found in the queue-4.9 subdirectory.

If you, or anyone else, feels it should not be added to the stable tree, please let <[email protected]> know about it.

From: Josh Poimboeuf <[email protected]>
Date: Mon, 15 Jan 2018 11:00:54 -0600
Subject: objtool: Fix retpoline support for pre-ORC objtool
To: David Woodhouse <[email protected]>
Cc: [email protected], [email protected], [email protected], [email protected], [email protected], [email protected], [email protected], [email protected], [email protected], [email protected], [email protected], [email protected], [email protected], [email protected], [email protected]
Message-ID: <20180115170054.6baepkgihtla4nub@treble>
Content-Disposition: inline

From: Josh Poimboeuf <[email protected]>

Objtool 1.0 (pre-ORC) produces the following warning when it encounters a retpoline:

arch/x86/crypto/camellia-aesni-avx2-asm_64.o: warning: objtool: .altinstr_replacement+0xf: return instruction outside of a callable function

That warning is meant to catch GCC bugs and missing ENTRY/ENDPROC annotations, neither of which are applicable to alternatives. Silence the warning for alternative instructions, just like objtool 2.0 already does.

---
 tools/objtool/builtin-check.c |    8 ++++++++
 1 file changed, 8 insertions(+)

@@ -1230,6 +1230,14 @@ static int validate_uncallable_instructi
 
 	for_each_insn(file, insn) {
 		if (!insn->visited && insn->type == INSN_RETURN) {
+
+			/*
+			 * Don't warn about call instructions in unvisited
+			 * retpoline alternatives.
+			 */
+			if (!strcmp(insn->sec->name, ".altinstr_replacement"))
+				continue;
+
 			WARN_FUNC("return instruction outside of a callable function",
 				  insn->sec, insn->offset);
 			warnings++;

Patches currently in stable-queue which might be from [email protected] are

queue-4.9/x86-spectre-add-boot-time-option-to-select-spectre-v2-mitigation.patch queue-4.9/x86-retpoline-irq32-convert-assembler-indirect-jumps.patch queue-4.9/objtool-detect-jumps-to-retpoline-thunks.patch queue-4.9/x86-retpoline-hyperv-convert-assembler-indirect-jumps.patch queue-4.9/x86-retpoline-entry-convert-entry-assembler-indirect-jumps.patch queue-4.9/x86-asm-use-register-variable-to-get-stack-pointer-value.patch queue-4.9/x86-cpufeatures-add-x86_bug_cpu_insecure.patch queue-4.9/objtool-modules-discard-objtool-annotation-sections-for-modules.patch queue-4.9/x86-cpufeatures-make-cpu-bugs-sticky.patch queue-4.9/x86-retpoline-ftrace-convert-ftrace-assembler-indirect-jumps.patch queue-4.9/objtool-allow-alternatives-to-be-ignored.patch queue-4.9/x86-retpoline-crypto-convert-crypto-assembler-indirect-jumps.patch queue-4.9/selftests-x86-add-test_vsyscall.patch queue-4.9/x86-retpoline-xen-convert-xen-hypercall-indirect-jumps.patch queue-4.9/x86-cpu-merge-bugs.c-and-bugs_64.c.patch queue-4.9/x86-retpoline-checksum32-convert-assembler-indirect-jumps.patch queue-4.9/x86-retpoline-fill-return-stack-buffer-on-vmexit.patch queue-4.9/x86-retpoline-remove-compile-time-warning.patch queue-4.9/objtool-fix-retpoline-support-for-pre-orc-objtool.patch queue-4.9/x86-retpoline-add-initial-retpoline-support.patch

Wonderful! Thanks so much for this, it works great for me, now queued up.

greg k-h