Re: [PATCH 00/21] objtool: vmlinux.o and CLANG LTO support

[Sedat Dilek]

On Fri, Jan 15, 2021 at 8:52 PM Josh Poimboeuf <jpoimboe@xxxxxxxxxx> wrote:
>
> On Thu, Jan 14, 2021 at 04:41:28PM -0800, Sami Tolvanen wrote:
> > Hi Josh,
> >
> > On Thu, Jan 14, 2021 at 11:40 AM Josh Poimboeuf <jpoimboe@xxxxxxxxxx> wrote:
> > >
> > > Add support for proper vmlinux.o validation, which will be needed for
> > > Sami's upcoming x86 LTO set.  (And vmlinux validation is the future for
> > > objtool anyway, for other reasons.)
> > >
> > > This isn't 100% done -- most notably, crypto still needs to be supported
> > > -- but I think this gets us most of the way there.
> > >
> > > This can also be found at
> > >
> > >   git://git.kernel.org/pub/scm/linux/kernel/git/jpoimboe/linux.git objtool-vmlinux
> > >
> > > And for more testing it can be combined with Sami's x86 LTO patches:
> > >
> > >   https://github.com/samitolvanen/linux clang-lto
> >
> > Thank you for sending these! I applied this series on top of the
> > clang-lto tree and built allyesconfig with LTO_CLANG enabled and the
> > following crypto options disabled:
> >
> > CRYPTO_AES_NI_INTEL
> > CRYPTO_CAMELLIA_AESNI_AVX2_X86_64
> > CRYPTO_SHA1_SSSE3
> > CRYPTO_SHA256_SSSE3
> > CRYPTO_SHA512_SSSE3
> > CRYPTO_CRC32C_INTEL
> >
> > I can confirm that all the warnings I previously saw are now fixed,
> > but I'm seeing a few new ones:
> >
> > vmlinux.o: warning: objtool: balance_leaf_when_delete()+0x17d4: stack
> > state mismatch: cfa1=7+192 cfa2=7+176
> > vmlinux.o: warning: objtool: internal_move_pointers_items()+0x9f7:
> > stack state mismatch: cfa1=7+160 cfa2=7+176
> > vmlinux.o: warning: objtool: strncpy_from_user()+0x181: call to
> > do_strncpy_from_user() with UACCESS enabled
> > vmlinux.o: warning: objtool: strnlen_user()+0x12b: call to
> > do_strnlen_user() with UACCESS enabled
> > vmlinux.o: warning: objtool: i915_gem_execbuffer2_ioctl()+0x390: call
> > to __ubsan_handle_negate_overflow() with UACCESS enabled
> > vmlinux.o: warning: objtool: .text.snd_trident_free_voice: unexpected
> > end of section
> >
> > I haven't had a chance to take a closer look yet, but some of these
> > are probably related to
> > https://github.com/ClangBuiltLinux/linux/issues/1192. However, I can
> > reproduce these also with ToT Clang, not just with Clang 11.
>
> Thanks, I'm able to reproduce these.  Will take a look.
>

AFAICS, that misses the v2 diff (see attachment) you sent me when
dealing with objtool-vmlinux and clang-cfi.
It does not cleanly apply with the combination of your objtool-vmlinux
Git and clang-cfi Git.


- Sedat -
diff --git a/tools/objtool/check.c b/tools/objtool/check.c
index 3d6cca126178..c8b2d26f4957 100644
--- a/tools/objtool/check.c
+++ b/tools/objtool/check.c
@@ -838,37 +838,6 @@ static int add_ignore_alternatives(struct objtool_file *file)
 	return 0;
 }
 
-/*
- * CONFIG_CFI_CLANG: Check if the section is a CFI jump table or a
- * compiler-generated CFI handler.
- */
-static bool is_cfi_section(struct section *sec)
-{
-	return (sec->name &&
-		(!strncmp(sec->name, ".text..L.cfi.jumptable", 22) ||
-		 !strcmp(sec->name, ".text.__cfi_check")));
-}
-
-/*
- * CONFIG_CFI_CLANG: Ignore CFI jump tables.
- */
-static void add_cfi_jumptables(struct objtool_file *file)
-{
-	struct section *sec;
-	struct symbol *func;
-	struct instruction *insn;
-
-	for_each_sec(file, sec) {
-		if (!is_cfi_section(sec))
-			continue;
-
-		list_for_each_entry(func, &sec->symbol_list, list) {
-			sym_for_each_insn(file, func, insn)
-				insn->ignore = true;
-		}
-	}
-}
-
 /*
  * Find the destination instructions for all jumps.
  */
@@ -939,9 +908,6 @@ static int add_jump_destinations(struct objtool_file *file)
 			if (!strcmp(insn->sec->name, ".altinstr_replacement"))
 				continue;
 
-			if (is_cfi_section(insn->sec))
-				continue;
-
 			WARN_FUNC("can't find jump dest instruction at %s+0x%lx",
 				  insn->sec, insn->offset, dest_sec->name,
 				  dest_off);
@@ -1049,9 +1015,6 @@ static int add_call_destinations(struct objtool_file *file)
 			insn->call_dest = find_call_destination(reloc->sym->sec,
 								dest_off);
 			if (!insn->call_dest) {
-				if (is_cfi_section(reloc->sym->sec))
-					continue;
-
 				WARN_FUNC("can't find call dest symbol at %s+0x%lx",
 					  insn->sec, insn->offset,
 					  reloc->sym->sec->name,
@@ -1791,7 +1754,6 @@ static int decode_sections(struct objtool_file *file)
 
 	add_ignores(file);
 	add_uaccess_safe(file);
-	add_cfi_jumptables(file);
 
 	ret = add_ignore_alternatives(file);
 	if (ret)
@@ -2654,8 +2616,7 @@ static int validate_branch(struct objtool_file *file, struct symbol *func,
 			if (dead_end_function(file, insn->call_dest))
 				return 0;
 
-			if (insn->type == INSN_CALL && insn->call_dest &&
-					insn->call_dest->static_call_tramp) {
+			if (insn->type == INSN_CALL && insn->call_dest->static_call_tramp) {
 				list_add_tail(&insn->static_call_node,
 					      &file->static_call_list);
 			}
diff --git a/tools/objtool/elf.c b/tools/objtool/elf.c
index ccee8fc331f0..b3b307bf7ec9 100644
--- a/tools/objtool/elf.c
+++ b/tools/objtool/elf.c
@@ -350,6 +350,11 @@ static int read_sections(struct elf *elf)
 		}
 		sec->len = sec->sh.sh_size;
 
+		/* Detect -fsanitize=cfi related sections */
+		if (!strcmp(sec->name, ".text.__cfi_check") ||
+		    !strncmp(sec->name, ".text..L.cfi.jumptable", 22))
+			sec->cfi_jt = true;
+
 		list_add_tail(&sec->list, &elf->sections);
 		elf_hash_add(elf->section_hash, &sec->hash, sec->idx);
 		elf_hash_add(elf->section_name_hash, &sec->name_hash, str_hash(sec->name));
@@ -606,6 +611,33 @@ static int read_relocs(struct elf *elf)
 				return -1;
 			}
 
+			if (reloc->sym->sec->cfi_jt) {
+				struct symbol *sym = reloc->sym;
+				char *suffix;
+				char name[MAX_NAME_LEN + 1];
+				size_t name_len;
+				struct symbol *new_sym;
+
+				if (sym->type == STT_SECTION)
+					sym = find_func_by_offset(sym->sec,
+								  reloc->addend);
+				if (sym) {
+					suffix = strstr(sym->name, ".cfi_jt");
+					if (suffix) {
+						name_len = suffix - sym->name;
+						strncpy(name, sym->name, name_len);
+						name[name_len] = '\0';
+						new_sym = find_symbol_by_name(elf, name);
+						if (!new_sym) {
+							WARN("wtf");
+							return -1;
+						}
+
+						reloc->sym = new_sym;
+					}
+				}
+			}
+
 			elf_add_reloc(elf, reloc);
 			nr_reloc++;
 		}
diff --git a/tools/objtool/elf.h b/tools/objtool/elf.h
index e6890cc70a25..bcc524d73f51 100644
--- a/tools/objtool/elf.h
+++ b/tools/objtool/elf.h
@@ -39,7 +39,7 @@ struct section {
 	char *name;
 	int idx;
 	unsigned int len;
-	bool changed, text, rodata, noinstr;
+	bool changed, text, rodata, noinstr, cfi_jt;
 };
 
 struct symbol {
-- 
2.30.0