From: Peter Zijlstra <peterz@infradead.org>
To: x86@kernel.org, joao@overdrivepizza.com, hjl.tools@gmail.com,
jpoimboe@redhat.com, andrew.cooper3@citrix.com
Cc: linux-kernel@vger.kernel.org, peterz@infradead.org,
ndesaulniers@google.com, keescook@chromium.org,
samitolvanen@google.com, mark.rutland@arm.com,
alyssa.milburn@intel.com, mbenes@suse.cz, rostedt@goodmis.org,
mhiramat@kernel.org, alexei.starovoitov@gmail.com
Subject: [PATCH v3 38/39] objtool: Find unused ENDBR instructions
Date: Thu, 03 Mar 2022 12:23:59 +0100 [thread overview]
Message-ID: <20220303112827.272113089@infradead.org> (raw)
In-Reply-To: 20220303112321.422525803@infradead.org
Find all ENDBR instructions which are never referenced and stick them
in a section such that the kernel can poison them, sealing the
functions from ever being an indirect call target.
This removes about 1-in-4 ENDBR instructions.
Signed-off-by: Peter Zijlstra (Intel) <peterz@infradead.org>
---
arch/x86/kernel/vmlinux.lds.S | 9 ++++
tools/objtool/check.c | 69 +++++++++++++++++++++++++++++++-
tools/objtool/include/objtool/objtool.h | 1
tools/objtool/objtool.c | 1
4 files changed, 78 insertions(+), 2 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_seal : AT(ADDR(.ibt_endbr_seal) - LOAD_OFFSET) {
+ __ibt_endbr_seal = .;
+ *(.ibt_endbr_seal)
+ __ibt_endbr_seal_end = .;
+ }
+#endif
+
/*
* struct alt_inst entries. From the header (alternative.h):
* "Alternative instructions for different CPU types or capabilities"
--- 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;
@@ -409,8 +410,9 @@ static int decode_instructions(struct ob
sym_for_each_insn(file, func, insn) {
insn->func = func;
- if (insn->type == INSN_ENDBR) {
+ if (insn->type == INSN_ENDBR && list_empty(&insn->call_node)) {
if (insn->offset == insn->func->offset) {
+ list_add_tail(&insn->call_node, &file->endbr_list);
file->nr_endbr++;
} else {
file->nr_endbr_int++;
@@ -739,6 +741,58 @@ static int create_retpoline_sites_sectio
return 0;
}
+static int create_ibt_endbr_seal_sections(struct objtool_file *file)
+{
+ struct instruction *insn;
+ struct section *sec;
+ int idx;
+
+ sec = find_section_by_name(file->elf, ".ibt_endbr_seal");
+ if (sec) {
+ WARN("file already has .ibt_endbr_seal, 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_seal", 0,
+ sizeof(int), idx);
+ if (!sec) {
+ WARN("elf_create_section: .ibt_endbr_seal");
+ 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_seal");
+ return -1;
+ }
+
+ idx++;
+ }
+
+ return 0;
+}
+
static int create_mcount_loc_sections(struct objtool_file *file)
{
struct section *sec;
@@ -3097,8 +3151,12 @@ 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;
@@ -3805,6 +3863,13 @@ int check(struct objtool_file *file)
if (ret < 0)
goto out;
warnings += ret;
+ }
+
+ if (ibt) {
+ ret = create_ibt_endbr_seal_sections(file);
+ if (ret < 0)
+ goto out;
+ warnings += ret;
}
if (stats) {
--- 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;
next prev parent reply other threads:[~2022-03-03 11:33 UTC|newest]
Thread overview: 64+ messages / expand[flat|nested] mbox.gz Atom feed top
2022-03-03 11:23 [PATCH v3 00/39] x86: Kernel IBT Peter Zijlstra
2022-03-03 11:23 ` [PATCH v3 01/39] static_call: Avoid building empty .static_call_sites Peter Zijlstra
2022-03-03 11:23 ` [PATCH v3 02/39] x86/module: Fix the paravirt vs alternative order Peter Zijlstra
2022-03-08 13:58 ` [tip: x86/urgent] " tip-bot2 for Peter Zijlstra
2022-03-03 11:23 ` [PATCH v3 03/39] objtool: Add --dry-run Peter Zijlstra
2022-03-03 11:23 ` [PATCH v3 04/39] x86/ibt: Base IBT bits Peter Zijlstra
2022-03-07 11:17 ` Peter Zijlstra
2022-03-07 12:25 ` Joao Moreira
2022-03-07 18:19 ` Nick Desaulniers
2022-03-03 11:23 ` [PATCH v3 05/39] x86/ibt: Add ANNOTATE_NOENDBR Peter Zijlstra
2022-03-04 18:59 ` Josh Poimboeuf
2022-03-04 20:22 ` Peter Zijlstra
2022-03-03 11:23 ` [PATCH v3 06/39] x86/text-patching: Make text_gen_insn() play nice with ANNOTATE_NOENDBR Peter Zijlstra
2022-03-03 11:23 ` [PATCH v3 07/39] x86/ibt,paravirt: Use text_gen_insn() for paravirt_patch() Peter Zijlstra
2022-03-03 11:23 ` [PATCH v3 08/39] x86/entry: Cleanup PARAVIRT Peter Zijlstra
2022-03-03 11:23 ` [PATCH v3 09/39] x86/entry,xen: Early rewrite of restore_regs_and_return_to_kernel() Peter Zijlstra
2022-03-03 11:23 ` [PATCH v3 10/39] x86/ibt,xen: Sprinkle the ENDBR Peter Zijlstra
2022-03-03 11:23 ` [PATCH v3 11/39] x86/ibt,entry: Sprinkle ENDBR dust Peter Zijlstra
2022-03-03 11:23 ` [PATCH v3 12/39] x86/linkage: Add ENDBR to SYM_FUNC_START*() Peter Zijlstra
2022-03-03 11:23 ` [PATCH v3 13/39] x86/ibt,paravirt: Sprinkle ENDBR Peter Zijlstra
2022-03-03 11:23 ` [PATCH v3 14/39] x86/ibt,crypto: Add ENDBR for the jump-table entries Peter Zijlstra
2022-03-03 11:23 ` [PATCH v3 15/39] x86/ibt,kvm: Add ENDBR to fastops Peter Zijlstra
2022-03-03 11:23 ` [PATCH v3 16/39] x86/ibt,ftrace: Search for __fentry__ location Peter Zijlstra
2022-03-03 11:23 ` [PATCH v3 17/39] x86/livepatch: Validate " Peter Zijlstra
2022-03-03 11:23 ` [PATCH v3 18/39] x86/ibt,ftrace: Make function-graph play nice Peter Zijlstra
2022-03-04 17:51 ` Josh Poimboeuf
2022-03-04 19:48 ` Peter Zijlstra
2022-03-04 21:03 ` Josh Poimboeuf
2022-03-04 21:44 ` Peter Zijlstra
2022-03-04 22:05 ` Josh Poimboeuf
2022-03-04 23:08 ` David Laight
2022-03-03 11:23 ` [PATCH v3 19/39] x86/ibt,kprobes: Cure sym+0 equals fentry woes Peter Zijlstra
2022-03-07 9:44 ` Masami Hiramatsu
2022-03-03 11:23 ` [PATCH v3 20/39] x86/ibt,bpf: Add ENDBR instructions to prologue and trampoline Peter Zijlstra
2022-03-03 11:23 ` [PATCH v3 21/39] x86/ibt,ftrace: Add ENDBR to samples/ftrace Peter Zijlstra
2022-03-03 11:23 ` [PATCH v3 22/39] x86/ibt: Add IBT feature, MSR and #CP handling Peter Zijlstra
2022-03-04 17:57 ` Josh Poimboeuf
2022-03-04 20:38 ` Peter Zijlstra
2022-03-04 18:07 ` Josh Poimboeuf
2022-03-04 20:39 ` Peter Zijlstra
2022-03-03 11:23 ` [PATCH v3 23/39] x86/alternative: Simplify int3_selftest_ip Peter Zijlstra
2022-03-04 18:02 ` Josh Poimboeuf
2022-03-04 18:09 ` Josh Poimboeuf
2022-03-03 11:23 ` [PATCH v3 24/39] x86/ibt: Disable IBT around firmware Peter Zijlstra
2022-03-03 11:23 ` [PATCH v3 25/39] x86/bugs: Disable Retpoline when IBT Peter Zijlstra
2022-03-04 17:39 ` Josh Poimboeuf
2022-03-03 11:23 ` [PATCH v3 26/39] x86/ibt: Annotate text references Peter Zijlstra
2022-03-03 11:23 ` [PATCH v3 27/39] x86/ibt,ftrace: Annotate ftrace code patching Peter Zijlstra
2022-03-03 11:23 ` [PATCH v3 28/39] x86/ibt,sev: Annotations Peter Zijlstra
2022-03-03 11:23 ` [PATCH v3 29/39] x86/ibt: Dont generate ENDBR in .discard.text Peter Zijlstra
2022-03-03 11:23 ` [PATCH v3 30/39] x86/ibt: Ensure module init/exit points have references Peter Zijlstra
2022-03-03 11:23 ` [PATCH v3 31/39] objtool: Rename --duplicate to --lto Peter Zijlstra
2022-03-03 11:23 ` [PATCH v3 32/39] Kbuild: Allow whole module objtool runs Peter Zijlstra
2022-03-03 11:23 ` [PATCH v3 33/39] objtool: Read the NOENDBR annotation Peter Zijlstra
2022-03-03 11:23 ` [PATCH v3 34/39] objtool: Have WARN_FUNC fall back to sym+off Peter Zijlstra
2022-03-03 11:23 ` [PATCH v3 35/39] objtool: Add IBT/ENDBR decoding Peter Zijlstra
2022-03-03 11:23 ` [PATCH v3 36/39] objtool: Validate IBT assumptions Peter Zijlstra
2022-03-03 11:23 ` [PATCH v3 37/39] objtool: Optionally WARN about unused ANNOTATE_NOENDBR Peter Zijlstra
2022-03-04 18:27 ` Josh Poimboeuf
2022-03-03 11:23 ` Peter Zijlstra [this message]
2022-03-03 11:24 ` [PATCH v3 39/39] x86/alternative: Use .ibt_endbr_seal to seal indirect calls Peter Zijlstra
2022-03-04 19:09 ` [PATCH v3 00/39] x86: Kernel IBT Josh Poimboeuf
2022-03-04 20:22 ` Peter Zijlstra
2022-03-04 21:39 ` Peter Zijlstra
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