summaryrefslogtreecommitdiff
path: root/tools
diff options
context:
space:
mode:
authorPeter Zijlstra <peterz@infradead.org>2022-06-15 00:16:03 +0300
committerBorislav Petkov <bp@suse.de>2022-06-27 11:34:00 +0300
commita09a6e2399ba0595c3042b3164f3ca68a3cff33e (patch)
treebf16062820b967a0b9c59169adf156eec8ed55a4 /tools
parent0fe4aeea9c01baabecc8c3afc7889c809d939bc2 (diff)
downloadlinux-a09a6e2399ba0595c3042b3164f3ca68a3cff33e.tar.xz
objtool: Add entry UNRET validation
Since entry asm is tricky, add a validation pass that ensures the retbleed mitigation has been done before the first actual RET instruction. Entry points are those that either have UNWIND_HINT_ENTRY, which acts as UNWIND_HINT_EMPTY but marks the instruction as an entry point, or those that have UWIND_HINT_IRET_REGS at +0. This is basically a variant of validate_branch() that is intra-function and it will simply follow all branches from marked entry points and ensures that all paths lead to ANNOTATE_UNRET_END. If a path hits RET or an indirection the path is a fail and will be reported. There are 3 ANNOTATE_UNRET_END instances: - UNTRAIN_RET itself - exception from-kernel; this path doesn't need UNTRAIN_RET - all early exceptions; these also don't need UNTRAIN_RET Signed-off-by: Peter Zijlstra (Intel) <peterz@infradead.org> Signed-off-by: Borislav Petkov <bp@suse.de> Reviewed-by: Josh Poimboeuf <jpoimboe@kernel.org> Signed-off-by: Borislav Petkov <bp@suse.de>
Diffstat (limited to 'tools')
-rw-r--r--tools/include/linux/objtool.h3
-rw-r--r--tools/objtool/builtin-check.c6
-rw-r--r--tools/objtool/check.c177
-rw-r--r--tools/objtool/include/objtool/builtin.h1
-rw-r--r--tools/objtool/include/objtool/check.h11
5 files changed, 187 insertions, 11 deletions
diff --git a/tools/include/linux/objtool.h b/tools/include/linux/objtool.h
index 15b940ec1eac..b026f1ae39c6 100644
--- a/tools/include/linux/objtool.h
+++ b/tools/include/linux/objtool.h
@@ -32,11 +32,14 @@ struct unwind_hint {
*
* UNWIND_HINT_FUNC: Generate the unwind metadata of a callable function.
* Useful for code which doesn't have an ELF function annotation.
+ *
+ * UNWIND_HINT_ENTRY: machine entry without stack, SYSCALL/SYSENTER etc.
*/
#define UNWIND_HINT_TYPE_CALL 0
#define UNWIND_HINT_TYPE_REGS 1
#define UNWIND_HINT_TYPE_REGS_PARTIAL 2
#define UNWIND_HINT_TYPE_FUNC 3
+#define UNWIND_HINT_TYPE_ENTRY 4
#ifdef CONFIG_OBJTOOL
diff --git a/tools/objtool/builtin-check.c b/tools/objtool/builtin-check.c
index f4c3a5091737..c063e1ff96b2 100644
--- a/tools/objtool/builtin-check.c
+++ b/tools/objtool/builtin-check.c
@@ -68,6 +68,7 @@ const struct option check_options[] = {
OPT_BOOLEAN('n', "noinstr", &opts.noinstr, "validate noinstr rules"),
OPT_BOOLEAN('o', "orc", &opts.orc, "generate ORC metadata"),
OPT_BOOLEAN('r', "retpoline", &opts.retpoline, "validate and annotate retpoline usage"),
+ OPT_BOOLEAN(0, "unret", &opts.unret, "validate entry unret placement"),
OPT_BOOLEAN('l', "sls", &opts.sls, "validate straight-line-speculation mitigations"),
OPT_BOOLEAN('s', "stackval", &opts.stackval, "validate frame pointer rules"),
OPT_BOOLEAN('t', "static-call", &opts.static_call, "annotate static calls"),
@@ -163,6 +164,11 @@ static bool link_opts_valid(struct objtool_file *file)
return false;
}
+ if (opts.unret) {
+ ERROR("--unret requires --link");
+ return false;
+ }
+
return true;
}
diff --git a/tools/objtool/check.c b/tools/objtool/check.c
index 7dc378156a63..822a490e6d87 100644
--- a/tools/objtool/check.c
+++ b/tools/objtool/check.c
@@ -2032,16 +2032,24 @@ static int read_unwind_hints(struct objtool_file *file)
insn->hint = true;
- if (opts.ibt && hint->type == UNWIND_HINT_TYPE_REGS_PARTIAL) {
+ if (hint->type == UNWIND_HINT_TYPE_REGS_PARTIAL) {
struct symbol *sym = find_symbol_by_offset(insn->sec, insn->offset);
- if (sym && sym->bind == STB_GLOBAL &&
- insn->type != INSN_ENDBR && !insn->noendbr) {
- WARN_FUNC("UNWIND_HINT_IRET_REGS without ENDBR",
- insn->sec, insn->offset);
+ if (sym && sym->bind == STB_GLOBAL) {
+ if (opts.ibt && insn->type != INSN_ENDBR && !insn->noendbr) {
+ WARN_FUNC("UNWIND_HINT_IRET_REGS without ENDBR",
+ insn->sec, insn->offset);
+ }
+
+ insn->entry = 1;
}
}
+ if (hint->type == UNWIND_HINT_TYPE_ENTRY) {
+ hint->type = UNWIND_HINT_TYPE_CALL;
+ insn->entry = 1;
+ }
+
if (hint->type == UNWIND_HINT_TYPE_FUNC) {
insn->cfi = &func_cfi;
continue;
@@ -2116,8 +2124,9 @@ static int read_retpoline_hints(struct objtool_file *file)
if (insn->type != INSN_JUMP_DYNAMIC &&
insn->type != INSN_CALL_DYNAMIC &&
- insn->type != INSN_RETURN) {
- WARN_FUNC("retpoline_safe hint not an indirect jump/call/ret",
+ insn->type != INSN_RETURN &&
+ insn->type != INSN_NOP) {
+ WARN_FUNC("retpoline_safe hint not an indirect jump/call/ret/nop",
insn->sec, insn->offset);
return -1;
}
@@ -3305,8 +3314,8 @@ static int validate_branch(struct objtool_file *file, struct symbol *func,
return 1;
}
- visited = 1 << state.uaccess;
- if (insn->visited) {
+ visited = VISITED_BRANCH << state.uaccess;
+ if (insn->visited & VISITED_BRANCH_MASK) {
if (!insn->hint && !insn_cfi_match(insn, &state.cfi))
return 1;
@@ -3520,6 +3529,145 @@ static int validate_unwind_hints(struct objtool_file *file, struct section *sec)
return warnings;
}
+/*
+ * Validate rethunk entry constraint: must untrain RET before the first RET.
+ *
+ * Follow every branch (intra-function) and ensure ANNOTATE_UNRET_END comes
+ * before an actual RET instruction.
+ */
+static int validate_entry(struct objtool_file *file, struct instruction *insn)
+{
+ struct instruction *next, *dest;
+ int ret, warnings = 0;
+
+ for (;;) {
+ next = next_insn_to_validate(file, insn);
+
+ if (insn->visited & VISITED_ENTRY)
+ return 0;
+
+ insn->visited |= VISITED_ENTRY;
+
+ if (!insn->ignore_alts && !list_empty(&insn->alts)) {
+ struct alternative *alt;
+ bool skip_orig = false;
+
+ list_for_each_entry(alt, &insn->alts, list) {
+ if (alt->skip_orig)
+ skip_orig = true;
+
+ ret = validate_entry(file, alt->insn);
+ if (ret) {
+ if (opts.backtrace)
+ BT_FUNC("(alt)", insn);
+ return ret;
+ }
+ }
+
+ if (skip_orig)
+ return 0;
+ }
+
+ switch (insn->type) {
+
+ case INSN_CALL_DYNAMIC:
+ case INSN_JUMP_DYNAMIC:
+ case INSN_JUMP_DYNAMIC_CONDITIONAL:
+ WARN_FUNC("early indirect call", insn->sec, insn->offset);
+ return 1;
+
+ case INSN_JUMP_UNCONDITIONAL:
+ case INSN_JUMP_CONDITIONAL:
+ if (!is_sibling_call(insn)) {
+ if (!insn->jump_dest) {
+ WARN_FUNC("unresolved jump target after linking?!?",
+ insn->sec, insn->offset);
+ return -1;
+ }
+ ret = validate_entry(file, insn->jump_dest);
+ if (ret) {
+ if (opts.backtrace) {
+ BT_FUNC("(branch%s)", insn,
+ insn->type == INSN_JUMP_CONDITIONAL ? "-cond" : "");
+ }
+ return ret;
+ }
+
+ if (insn->type == INSN_JUMP_UNCONDITIONAL)
+ return 0;
+
+ break;
+ }
+
+ /* fallthrough */
+ case INSN_CALL:
+ dest = find_insn(file, insn->call_dest->sec,
+ insn->call_dest->offset);
+ if (!dest) {
+ WARN("Unresolved function after linking!?: %s",
+ insn->call_dest->name);
+ return -1;
+ }
+
+ ret = validate_entry(file, dest);
+ if (ret) {
+ if (opts.backtrace)
+ BT_FUNC("(call)", insn);
+ return ret;
+ }
+ /*
+ * If a call returns without error, it must have seen UNTRAIN_RET.
+ * Therefore any non-error return is a success.
+ */
+ return 0;
+
+ case INSN_RETURN:
+ WARN_FUNC("RET before UNTRAIN", insn->sec, insn->offset);
+ return 1;
+
+ case INSN_NOP:
+ if (insn->retpoline_safe)
+ return 0;
+ break;
+
+ default:
+ break;
+ }
+
+ if (!next) {
+ WARN_FUNC("teh end!", insn->sec, insn->offset);
+ return -1;
+ }
+ insn = next;
+ }
+
+ return warnings;
+}
+
+/*
+ * Validate that all branches starting at 'insn->entry' encounter UNRET_END
+ * before RET.
+ */
+static int validate_unret(struct objtool_file *file)
+{
+ struct instruction *insn;
+ int ret, warnings = 0;
+
+ for_each_insn(file, insn) {
+ if (!insn->entry)
+ continue;
+
+ ret = validate_entry(file, insn);
+ if (ret < 0) {
+ WARN_FUNC("Failed UNRET validation", insn->sec, insn->offset);
+ return ret;
+ }
+ warnings += ret;
+ }
+
+ return warnings;
+}
+
static int validate_retpoline(struct objtool_file *file)
{
struct instruction *insn;
@@ -4039,6 +4187,17 @@ int check(struct objtool_file *file)
warnings += ret;
}
+ if (opts.unret) {
+ /*
+ * Must be after validate_branch() and friends, it plays
+ * further games with insn->visited.
+ */
+ ret = validate_unret(file);
+ if (ret < 0)
+ return ret;
+ warnings += ret;
+ }
+
if (opts.ibt) {
ret = validate_ibt(file);
if (ret < 0)
diff --git a/tools/objtool/include/objtool/builtin.h b/tools/objtool/include/objtool/builtin.h
index 280ea18b7f2b..0c476b0b40a3 100644
--- a/tools/objtool/include/objtool/builtin.h
+++ b/tools/objtool/include/objtool/builtin.h
@@ -19,6 +19,7 @@ struct opts {
bool noinstr;
bool orc;
bool retpoline;
+ bool unret;
bool sls;
bool stackval;
bool static_call;
diff --git a/tools/objtool/include/objtool/check.h b/tools/objtool/include/objtool/check.h
index f10d7374f388..0eeedeacbefb 100644
--- a/tools/objtool/include/objtool/check.h
+++ b/tools/objtool/include/objtool/check.h
@@ -51,8 +51,10 @@ struct instruction {
ignore_alts : 1,
hint : 1,
retpoline_safe : 1,
- noendbr : 1;
- /* 2 bit hole */
+ noendbr : 1,
+ entry : 1;
+ /* 1 bit hole */
+
s8 instr;
u8 visited;
/* u8 hole */
@@ -69,6 +71,11 @@ struct instruction {
struct cfi_state *cfi;
};
+#define VISITED_BRANCH 0x01
+#define VISITED_BRANCH_UACCESS 0x02
+#define VISITED_BRANCH_MASK 0x03
+#define VISITED_ENTRY 0x04
+
static inline bool is_static_jump(struct instruction *insn)
{
return insn->type == INSN_JUMP_CONDITIONAL ||