objtool: Add straight-line-speculation validation

Teach objtool to validate the straight-line-speculation constraints:

 - speculation trap after indirect calls
 - speculation trap after RET

Notable: when an instruction is annotated RETPOLINE_SAFE, indicating
  speculation isn't a problem, also don't care about sls for that
  instruction.

Signed-off-by: Peter Zijlstra (Intel) <peterz@infradead.org>
Signed-off-by: Borislav Petkov <bp@suse.de>
Link: https://lore.kernel.org/r/20211204134908.023037659@infradead.org

diff --git a/tools/objtool/arch/x86/decode.c b/tools/objtool/arch/x86/decode.c
index 4d6d7fc..c10ef78 100644 (file)
--- a/tools/objtool/arch/x86/decode.c
+++ b/tools/objtool/arch/x86/decode.c
@@ -531,6 +531,11 @@ int arch_decode_instruction(struct objtool_file *file, const struct section *sec
                }
                break;
 
+       case 0xcc:
+               /* int3 */
+               *type = INSN_TRAP;
+               break;
+
        case 0xe3:
                /* jecxz/jrcxz */
                *type = INSN_JUMP_CONDITIONAL;
@@ -697,10 +702,10 @@ const char *arch_ret_insn(int len)
 {
        static const char ret[5][5] = {
                { BYTE_RET },
-               { BYTE_RET, BYTES_NOP1 },
-               { BYTE_RET, BYTES_NOP2 },
-               { BYTE_RET, BYTES_NOP3 },
-               { BYTE_RET, BYTES_NOP4 },
+               { BYTE_RET, 0xcc },
+               { BYTE_RET, 0xcc, BYTES_NOP1 },
+               { BYTE_RET, 0xcc, BYTES_NOP2 },
+               { BYTE_RET, 0xcc, BYTES_NOP3 },
        };
 
        if (len < 1 || len > 5) {

diff --git a/tools/objtool/builtin-check.c b/tools/objtool/builtin-check.c
index 8b38b5d..38070f2 100644 (file)
--- a/tools/objtool/builtin-check.c
+++ b/tools/objtool/builtin-check.c
@@ -20,7 +20,7 @@
 #include <objtool/objtool.h>
 
 bool no_fp, no_unreachable, retpoline, module, backtrace, uaccess, stats,
-     validate_dup, vmlinux, mcount, noinstr, backup;
+     validate_dup, vmlinux, mcount, noinstr, backup, sls;
 
 static const char * const check_usage[] = {
        "objtool check [<options>] file.o",
@@ -45,6 +45,7 @@ const struct option check_options[] = {
        OPT_BOOLEAN('l', "vmlinux", &vmlinux, "vmlinux.o validation"),
        OPT_BOOLEAN('M', "mcount", &mcount, "generate __mcount_loc"),
        OPT_BOOLEAN('B', "backup", &backup, "create .orig files before modification"),
+       OPT_BOOLEAN('S', "sls", &sls, "validate straight-line-speculation"),
        OPT_END(),
 };
 

diff --git a/tools/objtool/check.c b/tools/objtool/check.c
index 2173582..e28172f 100644 (file)
--- a/tools/objtool/check.c
+++ b/tools/objtool/check.c
@@ -3084,6 +3084,12 @@ static int validate_branch(struct objtool_file *file, struct symbol *func,
                switch (insn->type) {
 
                case INSN_RETURN:
+                       if (next_insn && next_insn->type == INSN_TRAP) {
+                               next_insn->ignore = true;
+                       } else if (sls && !insn->retpoline_safe) {
+                               WARN_FUNC("missing int3 after ret",
+                                         insn->sec, insn->offset);
+                       }
                        return validate_return(func, insn, &state);
 
                case INSN_CALL:
@@ -3127,6 +3133,14 @@ static int validate_branch(struct objtool_file *file, struct symbol *func,
                        break;
 
                case INSN_JUMP_DYNAMIC:
+                       if (next_insn && next_insn->type == INSN_TRAP) {
+                               next_insn->ignore = true;
+                       } else if (sls && !insn->retpoline_safe) {
+                               WARN_FUNC("missing int3 after indirect jump",
+                                         insn->sec, insn->offset);
+                       }
+
+                       /* fallthrough */
                case INSN_JUMP_DYNAMIC_CONDITIONAL:
                        if (is_sibling_call(insn)) {
                                ret = validate_sibling_call(file, insn, &state);

diff --git a/tools/objtool/include/objtool/arch.h b/tools/objtool/include/objtool/arch.h
index 589ff58..76bae30 100644 (file)
--- a/tools/objtool/include/objtool/arch.h
+++ b/tools/objtool/include/objtool/arch.h
@@ -26,6 +26,7 @@ enum insn_type {
        INSN_CLAC,
        INSN_STD,
        INSN_CLD,
+       INSN_TRAP,
        INSN_OTHER,
 };
 

diff --git a/tools/objtool/include/objtool/builtin.h b/tools/objtool/include/objtool/builtin.h
index 15ac0b7..89ba869 100644 (file)
--- a/tools/objtool/include/objtool/builtin.h
+++ b/tools/objtool/include/objtool/builtin.h
@@ -9,7 +9,7 @@
 
 extern const struct option check_options[];
 extern bool no_fp, no_unreachable, retpoline, module, backtrace, uaccess, stats,
-            validate_dup, vmlinux, mcount, noinstr, backup;
+            validate_dup, vmlinux, mcount, noinstr, backup, sls;
 
 extern int cmd_parse_options(int argc, const char **argv, const char * const usage[]);