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Subject[PATCH 4.15 098/146] objtool: Add retpoline validation
Date
4.15-stable review patch.  If anyone has any objections, please let me know.

------------------

From: Peter Zijlstra <peterz@infradead.org>

commit b5bc2231b8ad4387c9641f235ca0ad8cd300b6df upstream.

David requested a objtool validation pass for CONFIG_RETPOLINE=y enabled
builds, where it validates no unannotated indirect jumps or calls are
left.

Add an additional .discard.retpoline_safe section to allow annotating
the few indirect sites that are required and safe.

Requested-by: David Woodhouse <dwmw2@infradead.org>
Signed-off-by: Peter Zijlstra (Intel) <peterz@infradead.org>
Reviewed-by: David Woodhouse <dwmw@amazon.co.uk>
Acked-by: Thomas Gleixner <tglx@linutronix.de>
Acked-by: Josh Poimboeuf <jpoimboe@redhat.com>
Cc: Andy Lutomirski <luto@kernel.org>
Cc: Arjan van de Ven <arjan@linux.intel.com>
Cc: Borislav Petkov <bp@alien8.de>
Cc: Dan Williams <dan.j.williams@intel.com>
Cc: Dave Hansen <dave.hansen@linux.intel.com>
Cc: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
Cc: Linus Torvalds <torvalds@linux-foundation.org>
Cc: Peter Zijlstra <peterz@infradead.org>
Signed-off-by: Ingo Molnar <mingo@kernel.org>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

---
scripts/Makefile.build | 4 +
tools/objtool/builtin-check.c | 3 -
tools/objtool/builtin.h | 2
tools/objtool/check.c | 86 +++++++++++++++++++++++++++++++++++++++++-
tools/objtool/check.h | 1
5 files changed, 93 insertions(+), 3 deletions(-)

--- a/scripts/Makefile.build
+++ b/scripts/Makefile.build
@@ -264,6 +264,10 @@ objtool_args += --no-unreachable
else
objtool_args += $(call cc-ifversion, -lt, 0405, --no-unreachable)
endif
+ifdef CONFIG_RETPOLINE
+ objtool_args += --retpoline
+endif
+

ifdef CONFIG_MODVERSIONS
objtool_o = $(@D)/.tmp_$(@F)
--- a/tools/objtool/builtin-check.c
+++ b/tools/objtool/builtin-check.c
@@ -29,7 +29,7 @@
#include "builtin.h"
#include "check.h"

-bool no_fp, no_unreachable;
+bool no_fp, no_unreachable, retpoline;

static const char * const check_usage[] = {
"objtool check [<options>] file.o",
@@ -39,6 +39,7 @@ static const char * const check_usage[]
const struct option check_options[] = {
OPT_BOOLEAN('f', "no-fp", &no_fp, "Skip frame pointer validation"),
OPT_BOOLEAN('u', "no-unreachable", &no_unreachable, "Skip 'unreachable instruction' warnings"),
+ OPT_BOOLEAN('r', "retpoline", &retpoline, "Validate retpoline assumptions"),
OPT_END(),
};

--- a/tools/objtool/builtin.h
+++ b/tools/objtool/builtin.h
@@ -20,7 +20,7 @@
#include <subcmd/parse-options.h>

extern const struct option check_options[];
-extern bool no_fp, no_unreachable;
+extern bool no_fp, no_unreachable, retpoline;

extern int cmd_check(int argc, const char **argv);
extern int cmd_orc(int argc, const char **argv);
--- a/tools/objtool/check.c
+++ b/tools/objtool/check.c
@@ -496,6 +496,7 @@ static int add_jump_destinations(struct
* disguise, so convert them accordingly.
*/
insn->type = INSN_JUMP_DYNAMIC;
+ insn->retpoline_safe = true;
continue;
} else {
/* sibling call */
@@ -547,7 +548,8 @@ static int add_call_destinations(struct
if (!insn->call_dest && !insn->ignore) {
WARN_FUNC("unsupported intra-function call",
insn->sec, insn->offset);
- WARN("If this is a retpoline, please patch it in with alternatives and annotate it with ANNOTATE_NOSPEC_ALTERNATIVE.");
+ if (retpoline)
+ WARN("If this is a retpoline, please patch it in with alternatives and annotate it with ANNOTATE_NOSPEC_ALTERNATIVE.");
return -1;
}

@@ -1107,6 +1109,54 @@ static int read_unwind_hints(struct objt
return 0;
}

+static int read_retpoline_hints(struct objtool_file *file)
+{
+ struct section *sec, *relasec;
+ struct instruction *insn;
+ struct rela *rela;
+ int i;
+
+ sec = find_section_by_name(file->elf, ".discard.retpoline_safe");
+ if (!sec)
+ return 0;
+
+ relasec = sec->rela;
+ if (!relasec) {
+ WARN("missing .rela.discard.retpoline_safe section");
+ return -1;
+ }
+
+ if (sec->len % sizeof(unsigned long)) {
+ WARN("retpoline_safe size mismatch: %d %ld", sec->len, sizeof(unsigned long));
+ return -1;
+ }
+
+ for (i = 0; i < sec->len / sizeof(unsigned long); i++) {
+ rela = find_rela_by_dest(sec, i * sizeof(unsigned long));
+ if (!rela) {
+ WARN("can't find rela for retpoline_safe[%d]", i);
+ return -1;
+ }
+
+ insn = find_insn(file, rela->sym->sec, rela->addend);
+ if (!insn) {
+ WARN("can't find insn for retpoline_safe[%d]", i);
+ return -1;
+ }
+
+ if (insn->type != INSN_JUMP_DYNAMIC &&
+ insn->type != INSN_CALL_DYNAMIC) {
+ WARN_FUNC("retpoline_safe hint not a indirect jump/call",
+ insn->sec, insn->offset);
+ return -1;
+ }
+
+ insn->retpoline_safe = true;
+ }
+
+ return 0;
+}
+
static int decode_sections(struct objtool_file *file)
{
int ret;
@@ -1145,6 +1195,10 @@ static int decode_sections(struct objtoo
if (ret)
return ret;

+ ret = read_retpoline_hints(file);
+ if (ret)
+ return ret;
+
return 0;
}

@@ -1890,6 +1944,29 @@ static int validate_unwind_hints(struct
return warnings;
}

+static int validate_retpoline(struct objtool_file *file)
+{
+ struct instruction *insn;
+ int warnings = 0;
+
+ for_each_insn(file, insn) {
+ if (insn->type != INSN_JUMP_DYNAMIC &&
+ insn->type != INSN_CALL_DYNAMIC)
+ continue;
+
+ if (insn->retpoline_safe)
+ continue;
+
+ WARN_FUNC("indirect %s found in RETPOLINE build",
+ insn->sec, insn->offset,
+ insn->type == INSN_JUMP_DYNAMIC ? "jump" : "call");
+
+ warnings++;
+ }
+
+ return warnings;
+}
+
static bool is_kasan_insn(struct instruction *insn)
{
return (insn->type == INSN_CALL &&
@@ -2050,6 +2127,13 @@ int check(const char *_objname, bool orc
if (list_empty(&file.insn_list))
goto out;

+ if (retpoline) {
+ ret = validate_retpoline(&file);
+ if (ret < 0)
+ return ret;
+ warnings += ret;
+ }
+
ret = validate_functions(&file);
if (ret < 0)
goto out;
--- a/tools/objtool/check.h
+++ b/tools/objtool/check.h
@@ -45,6 +45,7 @@ struct instruction {
unsigned char type;
unsigned long immediate;
bool alt_group, visited, dead_end, ignore, hint, save, restore, ignore_alts;
+ bool retpoline_safe;
struct symbol *call_dest;
struct instruction *jump_dest;
struct instruction *first_jump_src;

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