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Date: Thu, 24 Feb 2022 15:52:14 +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 36/39] objtool: Find unused ENDBR instructions
Find all unused ENDBR instructions and stick them in a section such
that the kernel can poison them.
Signed-off-by: Peter Zijlstra (Intel) <peterz@...radead.org>
---
arch/x86/kernel/vmlinux.lds.S | 9 ++++
tools/objtool/builtin-check.c | 3 -
tools/objtool/check.c | 72 +++++++++++++++++++++++++++++++-
tools/objtool/include/objtool/builtin.h | 2
tools/objtool/include/objtool/objtool.h | 1
tools/objtool/objtool.c | 1
6 files changed, 85 insertions(+), 3 deletions(-)
--- a/arch/x86/kernel/vmlinux.lds.S
+++ b/arch/x86/kernel/vmlinux.lds.S
@@ -285,6 +285,15 @@ SECTIONS
}
#endif
+#ifdef CONFIG_X86_KERNEL_IBT
+ . = ALIGN(8);
+ .ibt_endbr_sites : AT(ADDR(.ibt_endbr_sites) - LOAD_OFFSET) {
+ __ibt_endbr_sites = .;
+ *(.ibt_endbr_sites)
+ __ibt_endbr_sites_end = .;
+ }
+#endif
+
/*
* struct alt_inst entries. From the header (alternative.h):
* "Alternative instructions for different CPU types or capabilities"
--- a/tools/objtool/builtin-check.c
+++ b/tools/objtool/builtin-check.c
@@ -21,7 +21,7 @@
bool no_fp, no_unreachable, retpoline, module, backtrace, uaccess, stats,
lto, vmlinux, mcount, noinstr, backup, sls, dryrun,
- ibt, ibt_fix_direct;
+ ibt, ibt_fix_direct, ibt_seal;
static const char * const check_usage[] = {
"objtool check [<options>] file.o",
@@ -50,6 +50,7 @@ const struct option check_options[] = {
OPT_BOOLEAN(0, "dry-run", &dryrun, "don't write the modifications"),
OPT_BOOLEAN(0, "ibt", &ibt, "validate ENDBR placement"),
OPT_BOOLEAN(0, "ibt-fix-direct", &ibt_fix_direct, "fixup direct jmp/call to ENDBR"),
+ OPT_BOOLEAN(0, "ibt-seal", &ibt_seal, "list superfluous ENDBR instructions"),
OPT_END(),
};
--- a/tools/objtool/check.c
+++ b/tools/objtool/check.c
@@ -732,6 +732,58 @@ static int create_retpoline_sites_sectio
return 0;
}
+static int create_ibt_endbr_sites_sections(struct objtool_file *file)
+{
+ struct instruction *insn;
+ struct section *sec;
+ int idx;
+
+ sec = find_section_by_name(file->elf, ".ibt_endbr_sites");
+ if (sec) {
+ WARN("file already has .ibt_endbr_sites, skipping");
+ return 0;
+ }
+
+ idx = 0;
+ list_for_each_entry(insn, &file->endbr_list, call_node)
+ idx++;
+
+ if (stats) {
+ printf("ibt: ENDBR at function start: %d\n", file->nr_endbr);
+ printf("ibt: ENDBR inside functions: %d\n", file->nr_endbr_int);
+ printf("ibt: superfluous ENDBR: %d\n", idx);
+ }
+
+ if (!idx)
+ return 0;
+
+ sec = elf_create_section(file->elf, ".ibt_endbr_sites", 0,
+ sizeof(int), idx);
+ if (!sec) {
+ WARN("elf_create_section: .ibt_endbr_sites");
+ return -1;
+ }
+
+ idx = 0;
+ list_for_each_entry(insn, &file->endbr_list, call_node) {
+
+ int *site = (int *)sec->data->d_buf + idx;
+ *site = 0;
+
+ if (elf_add_reloc_to_insn(file->elf, sec,
+ idx * sizeof(int),
+ R_X86_64_PC32,
+ insn->sec, insn->offset)) {
+ WARN("elf_add_reloc_to_insn: .ibt_endbr_sites");
+ return -1;
+ }
+
+ idx++;
+ }
+
+ return 0;
+}
+
static int create_mcount_loc_sections(struct objtool_file *file)
{
struct section *sec;
@@ -1179,6 +1231,7 @@ static int add_jump_destinations(struct
for_each_insn(file, insn) {
if (insn->type == INSN_ENDBR && insn->func) {
if (insn->offset == insn->func->offset) {
+ list_add_tail(&insn->call_node, &file->endbr_list);
file->nr_endbr++;
} else {
file->nr_endbr_int++;
@@ -3633,8 +3687,12 @@ validate_ibt_reloc(struct objtool_file *
if (!dest)
return NULL;
- if (dest->type == INSN_ENDBR)
+ if (dest->type == INSN_ENDBR) {
+ if (!list_empty(&dest->call_node))
+ list_del_init(&dest->call_node);
+
return NULL;
+ }
if (reloc->sym->static_call_tramp)
return NULL;
@@ -3777,6 +3835,11 @@ int check(struct objtool_file *file)
return 1;
}
+ if (ibt_seal && !ibt_fix_direct) {
+ fprintf(stderr, "--ibt-seal requires: --ibt-fix-direct\n");
+ return 1;
+ }
+
arch_initial_func_cfi_state(&initial_func_cfi);
init_cfi_state(&init_cfi);
init_cfi_state(&func_cfi);
@@ -3854,6 +3917,13 @@ int check(struct objtool_file *file)
if (ret < 0)
goto out;
warnings += ret;
+ }
+
+ if (ibt_seal) {
+ ret = create_ibt_endbr_sites_sections(file);
+ if (ret < 0)
+ goto out;
+ warnings += ret;
}
if (stats) {
--- a/tools/objtool/include/objtool/builtin.h
+++ b/tools/objtool/include/objtool/builtin.h
@@ -10,7 +10,7 @@
extern const struct option check_options[];
extern bool no_fp, no_unreachable, retpoline, module, backtrace, uaccess, stats,
lto, vmlinux, mcount, noinstr, backup, sls, dryrun,
- ibt, ibt_fix_direct;
+ ibt, ibt_fix_direct, ibt_seal;
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
@@ -26,6 +26,7 @@ struct objtool_file {
struct list_head retpoline_call_list;
struct list_head static_call_list;
struct list_head mcount_loc_list;
+ struct list_head endbr_list;
bool ignore_unreachables, c_file, hints, rodata;
unsigned int nr_endbr;
--- a/tools/objtool/objtool.c
+++ b/tools/objtool/objtool.c
@@ -128,6 +128,7 @@ struct objtool_file *objtool_open_read(c
INIT_LIST_HEAD(&file.retpoline_call_list);
INIT_LIST_HEAD(&file.static_call_list);
INIT_LIST_HEAD(&file.mcount_loc_list);
+ INIT_LIST_HEAD(&file.endbr_list);
file.c_file = !vmlinux && find_section_by_name(file.elf, ".comment");
file.ignore_unreachables = no_unreachable;
file.hints = false;
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