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Date: Thu, 24 Feb 2022 15:52:12 +0100
From: Peter Zijlstra <peterz@...radead.org>
To: x86@...nel.org, joao@...rdrivepizza.com, hjl.tools@...il.com,
jpoimboe@...hat.com, andrew.cooper3@...rix.com
Cc: linux-kernel@...r.kernel.org, peterz@...radead.org,
ndesaulniers@...gle.com, keescook@...omium.org,
samitolvanen@...gle.com, mark.rutland@....com,
alyssa.milburn@...el.com, mbenes@...e.cz, rostedt@...dmis.org,
mhiramat@...nel.org, alexei.starovoitov@...il.com
Subject: [PATCH v2 34/39] objtool: Validate IBT assumptions
Intel IBT requires that every indirect JMP/CALL targets an ENDBR
instructions, failing this #CP happens and we die. Similarly, all
exception entries should be ENDBR.
Find all code relocations and ensure they're either an ENDBR
instruction or ANNOTATE_NOENDBR. For the exceptions look for
UNWIND_HINT_IRET_REGS at sym+0 not being ENDBR.
Additionally, look for direct JMP/CALL instructions and warn if they
target an ENDBR instruction. This extra constraint comes from the
desire to poison unused ENDBR instructions.
NOTE: the changes in add_{call,jump}_destination() are to add a common
path after setting insn->{jump,call}_dest with both (source and
destination) instructions available.
Signed-off-by: Peter Zijlstra (Intel) <peterz@...radead.org>
---
tools/objtool/builtin-check.c | 4
tools/objtool/check.c | 255 +++++++++++++++++++++++++++++---
tools/objtool/include/objtool/builtin.h | 3
tools/objtool/include/objtool/objtool.h | 3
4 files changed, 243 insertions(+), 22 deletions(-)
--- a/tools/objtool/builtin-check.c
+++ b/tools/objtool/builtin-check.c
@@ -20,7 +20,8 @@
#include <objtool/objtool.h>
bool no_fp, no_unreachable, retpoline, module, backtrace, uaccess, stats,
- lto, vmlinux, mcount, noinstr, backup, sls, dryrun;
+ lto, vmlinux, mcount, noinstr, backup, sls, dryrun,
+ ibt;
static const char * const check_usage[] = {
"objtool check [<options>] file.o",
@@ -47,6 +48,7 @@ const struct option check_options[] = {
OPT_BOOLEAN('B', "backup", &backup, "create .orig files before modification"),
OPT_BOOLEAN('S', "sls", &sls, "validate straight-line-speculation"),
OPT_BOOLEAN(0, "dry-run", &dryrun, "don't write the modifications"),
+ OPT_BOOLEAN(0, "ibt", &ibt, "validate ENDBR placement"),
OPT_END(),
};
--- a/tools/objtool/check.c
+++ b/tools/objtool/check.c
@@ -380,6 +380,7 @@ static int decode_instructions(struct ob
memset(insn, 0, sizeof(*insn));
INIT_LIST_HEAD(&insn->alts);
INIT_LIST_HEAD(&insn->stack_ops);
+ INIT_LIST_HEAD(&insn->call_node);
insn->sec = sec;
insn->offset = offset;
@@ -1176,6 +1177,14 @@ static int add_jump_destinations(struct
unsigned long dest_off;
for_each_insn(file, insn) {
+ if (insn->type == INSN_ENDBR && insn->func) {
+ if (insn->offset == insn->func->offset) {
+ file->nr_endbr++;
+ } else {
+ file->nr_endbr_int++;
+ }
+ }
+
if (!is_static_jump(insn))
continue;
@@ -1192,10 +1201,14 @@ static int add_jump_destinations(struct
} else if (insn->func) {
/* internal or external sibling call (with reloc) */
add_call_dest(file, insn, reloc->sym, true);
- continue;
+
+ dest_sec = reloc->sym->sec;
+ dest_off = reloc->sym->offset +
+ arch_dest_reloc_offset(reloc->addend);
+
} else if (reloc->sym->sec->idx) {
dest_sec = reloc->sym->sec;
- dest_off = reloc->sym->sym.st_value +
+ dest_off = reloc->sym->offset +
arch_dest_reloc_offset(reloc->addend);
} else {
/* non-func asm code jumping to another file */
@@ -1205,6 +1218,10 @@ static int add_jump_destinations(struct
insn->jump_dest = find_insn(file, dest_sec, dest_off);
if (!insn->jump_dest) {
+ /* external symbol */
+ if (!vmlinux && insn->func)
+ continue;
+
/*
* This is a special case where an alt instruction
* jumps past the end of the section. These are
@@ -1219,6 +1236,16 @@ static int add_jump_destinations(struct
return -1;
}
+ if (ibt && insn->jump_dest->type == INSN_ENDBR &&
+ insn->jump_dest->func &&
+ insn->jump_dest->offset == insn->jump_dest->func->offset) {
+ if (reloc) {
+ WARN_FUNC("Direct RELOC jump to ENDBR", insn->sec, insn->offset);
+ } else {
+ WARN_FUNC("Direct IMM jump to ENDBR", insn->sec, insn->offset);
+ }
+ }
+
/*
* Cross-function jump.
*/
@@ -1246,7 +1273,8 @@ static int add_jump_destinations(struct
insn->jump_dest->func->pfunc = insn->func;
} else if (insn->jump_dest->func->pfunc != insn->func->pfunc &&
- insn->jump_dest->offset == insn->jump_dest->func->offset) {
+ ((insn->jump_dest->offset == insn->jump_dest->func->offset) ||
+ (insn->jump_dest->offset == insn->jump_dest->func->offset + 4))) {
/* internal sibling call (without reloc) */
add_call_dest(file, insn, insn->jump_dest->func, true);
}
@@ -1256,23 +1284,12 @@ static int add_jump_destinations(struct
return 0;
}
-static struct symbol *find_call_destination(struct section *sec, unsigned long offset)
-{
- struct symbol *call_dest;
-
- call_dest = find_func_by_offset(sec, offset);
- if (!call_dest)
- call_dest = find_symbol_by_offset(sec, offset);
-
- return call_dest;
-}
-
/*
* Find the destination instructions for all calls.
*/
static int add_call_destinations(struct objtool_file *file)
{
- struct instruction *insn;
+ struct instruction *insn, *target = NULL;
unsigned long dest_off;
struct symbol *dest;
struct reloc *reloc;
@@ -1284,7 +1301,21 @@ static int add_call_destinations(struct
reloc = insn_reloc(file, insn);
if (!reloc) {
dest_off = arch_jump_destination(insn);
- dest = find_call_destination(insn->sec, dest_off);
+
+ target = find_insn(file, insn->sec, dest_off);
+ if (!target) {
+ WARN_FUNC("direct call to nowhere", insn->sec, insn->offset);
+ return -1;
+ }
+ dest = target->func;
+ if (!dest)
+ dest = find_symbol_containing(insn->sec, dest_off);
+ if (!dest) {
+ WARN_FUNC("IMM can't find call dest symbol at %s+0x%lx",
+ insn->sec, insn->offset,
+ insn->sec->name, dest_off);
+ return -1;
+ }
add_call_dest(file, insn, dest, false);
@@ -1303,10 +1334,22 @@ static int add_call_destinations(struct
}
} else if (reloc->sym->type == STT_SECTION) {
- dest_off = arch_dest_reloc_offset(reloc->addend);
- dest = find_call_destination(reloc->sym->sec, dest_off);
+ struct section *dest_sec;
+
+ dest_sec = reloc->sym->sec;
+ dest_off = reloc->sym->offset +
+ arch_dest_reloc_offset(reloc->addend);
+
+ target = find_insn(file, dest_sec, dest_off);
+ if (!target) {
+ WARN_FUNC("direct call to nowhere", insn->sec, insn->offset);
+ return -1;
+ }
+ dest = target->func;
+ if (!dest)
+ dest = find_symbol_containing(dest_sec, dest_off);
if (!dest) {
- WARN_FUNC("can't find call dest symbol at %s+0x%lx",
+ WARN_FUNC("RELOC can't find call dest symbol at %s+0x%lx",
insn->sec, insn->offset,
reloc->sym->sec->name,
dest_off);
@@ -1317,9 +1360,27 @@ static int add_call_destinations(struct
} else if (reloc->sym->retpoline_thunk) {
add_retpoline_call(file, insn);
+ continue;
+
+ } else {
+ struct section *dest_sec;
+
+ dest_sec = reloc->sym->sec;
+ dest_off = reloc->sym->offset +
+ arch_dest_reloc_offset(reloc->addend);
+
+ target = find_insn(file, dest_sec, dest_off);
- } else
add_call_dest(file, insn, reloc->sym, false);
+ }
+
+ if (ibt && target && target->type == INSN_ENDBR) {
+ if (reloc) {
+ WARN_FUNC("Direct RELOC call to ENDBR", insn->sec, insn->offset);
+ } else {
+ WARN_FUNC("Direct IMM call to ENDBR", insn->sec, insn->offset);
+ }
+ }
}
return 0;
@@ -3053,6 +3114,8 @@ static struct instruction *next_insn_to_
return next_insn_same_sec(file, insn);
}
+static void validate_ibt_insn(struct objtool_file *file, struct instruction *insn);
+
/*
* Follow the branch starting at the given instruction, and recursively follow
* any other branches (jumps). Meanwhile, track the frame pointer state at
@@ -3101,6 +3164,17 @@ static int validate_branch(struct objtoo
if (insn->hint) {
state.cfi = *insn->cfi;
+ if (ibt) {
+ struct symbol *sym;
+
+ if (insn->cfi->type == UNWIND_HINT_TYPE_REGS_PARTIAL &&
+ (sym = find_symbol_by_offset(insn->sec, insn->offset)) &&
+ insn->type != INSN_ENDBR && !insn->noendbr) {
+ WARN_FUNC("IRET_REGS hint without ENDBR: %s",
+ insn->sec, insn->offset,
+ sym->name);
+ }
+ }
} else {
/* XXX track if we actually changed state.cfi */
@@ -3260,7 +3334,12 @@ static int validate_branch(struct objtoo
state.df = false;
break;
+ case INSN_NOP:
+ break;
+
default:
+ if (ibt)
+ validate_ibt_insn(file, insn);
break;
}
@@ -3506,6 +3585,130 @@ static int validate_functions(struct obj
return warnings;
}
+static struct instruction *
+validate_ibt_reloc(struct objtool_file *file, struct reloc *reloc)
+{
+ struct instruction *dest;
+ struct section *sec;
+ unsigned long off;
+
+ sec = reloc->sym->sec;
+ off = reloc->sym->offset + reloc->addend;
+
+ dest = find_insn(file, sec, off);
+ if (!dest)
+ return NULL;
+
+ if (dest->type == INSN_ENDBR)
+ return NULL;
+
+ if (reloc->sym->static_call_tramp)
+ return NULL;
+
+ return dest;
+}
+
+static void warn_noendbr(const char *msg, struct section *sec, unsigned long offset,
+ struct instruction *target)
+{
+ WARN_FUNC("%srelocation to !ENDBR: %s+0x%lx", sec, offset, msg,
+ target->func ? target->func->name : target->sec->name,
+ target->func ? target->offset - target->func->offset : target->offset);
+}
+
+static void validate_ibt_target(struct objtool_file *file, struct instruction *insn,
+ struct instruction *target)
+{
+ if (target->func && target->func == insn->func) {
+ /*
+ * Anything from->to self is either _THIS_IP_ or IRET-to-self.
+ *
+ * There is no sane way to annotate _THIS_IP_ since the compiler treats the
+ * relocation as a constant and is happy to fold in offsets, skewing any
+ * annotation we do, leading to vast amounts of false-positives.
+ *
+ * There's also compiler generated _THIS_IP_ through KCOV and
+ * such which we have no hope of annotating.
+ *
+ * As such, blanked accept self-references without issue.
+ */
+ return;
+ }
+
+ /*
+ * Annotated non-control flow target.
+ */
+ if (target->noendbr)
+ return;
+
+ warn_noendbr("", insn->sec, insn->offset, target);
+}
+
+static void validate_ibt_insn(struct objtool_file *file, struct instruction *insn)
+{
+ struct reloc *reloc = insn_reloc(file, insn);
+ struct instruction *target;
+
+ for (;;) {
+ if (!reloc)
+ return;
+
+ target = validate_ibt_reloc(file, reloc);
+ if (target)
+ validate_ibt_target(file, insn, target);
+
+ reloc = find_reloc_by_dest_range(file->elf, insn->sec, reloc->offset + 1,
+ (insn->offset + insn->len) - (reloc->offset + 1));
+ }
+}
+
+static int validate_ibt(struct objtool_file *file)
+{
+ struct section *sec;
+ struct reloc *reloc;
+
+ for_each_sec(file, sec) {
+ bool is_data;
+
+ /* already done in validate_branch() */
+ if (sec->sh.sh_flags & SHF_EXECINSTR)
+ continue;
+
+ if (!sec->reloc)
+ continue;
+
+ if (!strncmp(sec->name, ".orc", 4))
+ continue;
+
+ if (!strncmp(sec->name, ".discard", 8))
+ continue;
+
+ if (!strncmp(sec->name, ".debug", 6))
+ continue;
+
+ if (!strcmp(sec->name, "_error_injection_whitelist"))
+ continue;
+
+ if (!strcmp(sec->name, "_kprobe_blacklist"))
+ continue;
+
+ is_data = strstr(sec->name, ".data") || strstr(sec->name, ".rodata");
+
+ list_for_each_entry(reloc, &sec->reloc->reloc_list, list) {
+ struct instruction *target;
+
+ target = validate_ibt_reloc(file, reloc);
+ if (is_data && target && !target->noendbr) {
+ warn_noendbr("data ", reloc->sym->sec,
+ reloc->sym->offset + reloc->addend,
+ target);
+ }
+ }
+ }
+
+ return 0;
+}
+
static int validate_reachable_instructions(struct objtool_file *file)
{
struct instruction *insn;
@@ -3533,6 +3736,11 @@ int check(struct objtool_file *file)
return 1;
}
+ if (ibt && !lto) {
+ fprintf(stderr, "--ibt requires: --lto\n");
+ return 1;
+ }
+
arch_initial_func_cfi_state(&initial_func_cfi);
init_cfi_state(&init_cfi);
init_cfi_state(&func_cfi);
@@ -3579,6 +3787,13 @@ int check(struct objtool_file *file)
goto out;
warnings += ret;
+ if (ibt) {
+ ret = validate_ibt(file);
+ if (ret < 0)
+ goto out;
+ warnings += ret;
+ }
+
if (!warnings) {
ret = validate_reachable_instructions(file);
if (ret < 0)
--- a/tools/objtool/include/objtool/builtin.h
+++ b/tools/objtool/include/objtool/builtin.h
@@ -9,7 +9,8 @@
extern const struct option check_options[];
extern bool no_fp, no_unreachable, retpoline, module, backtrace, uaccess, stats,
- lto, vmlinux, mcount, noinstr, backup, sls, dryrun;
+ lto, vmlinux, mcount, noinstr, backup, sls, dryrun,
+ ibt;
extern int cmd_parse_options(int argc, const char **argv, const char * const usage[]);
--- a/tools/objtool/include/objtool/objtool.h
+++ b/tools/objtool/include/objtool/objtool.h
@@ -28,6 +28,9 @@ struct objtool_file {
struct list_head mcount_loc_list;
bool ignore_unreachables, c_file, hints, rodata;
+ unsigned int nr_endbr;
+ unsigned int nr_endbr_int;
+
unsigned long jl_short, jl_long;
unsigned long jl_nop_short, jl_nop_long;
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