From: Josh Poimboeuf <jpoimboe@redhat.com>
To: x86@kernel.org
Cc: linux-kernel@vger.kernel.org,
Peter Zijlstra <peterz@infradead.org>,
Sami Tolvanen <samitolvanen@google.com>,
Sedat Dilek <sedat.dilek@gmail.com>,
Kees Cook <keescook@chromium.org>,
Nick Desaulniers <ndesaulniers@google.com>,
clang-built-linux@googlegroups.com,
Miroslav Benes <mbenes@suse.cz>
Subject: [PATCH v2 11/20] objtool: Add CONFIG_CFI_CLANG support
Date: Thu, 21 Jan 2021 15:29:27 -0600 [thread overview]
Message-ID: <d743f4b36e120c06506567a9f87a062ae03da47f.1611263462.git.jpoimboe@redhat.com> (raw)
In-Reply-To: <cover.1611263461.git.jpoimboe@redhat.com>
The upcoming CONFIG_CFI_CLANG support uses -fsanitize=cfi, the
non-canonical version of which hijacks function entry by changing
function relocation references to point to an intermediary jump table.
For example:
Relocation section '.rela.discard.func_stack_frame_non_standard' at offset 0x37e018 contains 6 entries:
Offset Info Type Symbol's Value Symbol's Name + Addend
0000000000000000 0002944700000002 R_X86_64_PC32 00000000000023f0 do_suspend_lowlevel + 0
0000000000000008 0003c11900000001 R_X86_64_64 0000000000000008 xen_cpuid$e69bc59f4fade3b6f2b579b3934137df.cfi_jt + 0
0000000000000010 0003980900000001 R_X86_64_64 0000000000000060 machine_real_restart.cfi_jt + 0
0000000000000018 0003962b00000001 R_X86_64_64 0000000000000e18 kretprobe_trampoline.cfi_jt + 0
0000000000000020 000028f300000001 R_X86_64_64 0000000000000000 .rodata + 12
0000000000000028 000349f400000001 R_X86_64_64 0000000000000018 __crash_kexec.cfi_jt + 0
0000000000000060 <machine_real_restart.cfi_jt>:
60: e9 00 00 00 00 jmpq 65 <machine_real_restart.cfi_jt+0x5>
61: R_X86_64_PLT32 machine_real_restart-0x4
65: cc int3
66: cc int3
67: cc int3
This breaks objtool vmlinux validation in many ways, including static
call site detection and the STACK_FRAME_NON_STANDARD() macro.
Fix it by converting those relocations' symbol references back to their
original non-jump-table versions. Note this doesn't change the actual
relocations in the object itself, it just changes objtool's view of
them.
Reported-by: Sedat Dilek <sedat.dilek@gmail.com>
Signed-off-by: Josh Poimboeuf <jpoimboe@redhat.com>
---
tools/objtool/elf.c | 28 ++++++++++++++++++++++++++++
tools/objtool/include/objtool/elf.h | 2 +-
2 files changed, 29 insertions(+), 1 deletion(-)
diff --git a/tools/objtool/elf.c b/tools/objtool/elf.c
index e7d9c29fe78c..18b6fc4ca1f8 100644
--- a/tools/objtool/elf.c
+++ b/tools/objtool/elf.c
@@ -382,6 +382,11 @@ 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));
@@ -613,6 +618,29 @@ static int read_relocs(struct elf *elf)
return -1;
}
+ /*
+ * Deal with -fsanitize=cfi (CONFIG_CFI_CLANG), which
+ * hijacks function entry by arbitrarily changing a lot
+ * of relocation symbol references to refer to an
+ * intermediate jump table. Undo that conversion so
+ * objtool can make sense of things.
+ */
+ if (reloc->sym->sec->cfi_jt) {
+ struct symbol *func, *sym;
+
+ if (reloc->sym->type == STT_SECTION)
+ sym = find_func_by_offset(reloc->sym->sec,
+ reloc->addend);
+ else
+ sym = reloc->sym;
+
+ if (find_unsuffixed_func(elf, sym, ".cfi_jt", &func))
+ return -1;
+
+ if (func)
+ reloc->sym = func;
+ }
+
elf_add_reloc(elf, reloc);
nr_reloc++;
}
diff --git a/tools/objtool/include/objtool/elf.h b/tools/objtool/include/objtool/elf.h
index e6890cc70a25..bcc524d73f51 100644
--- a/tools/objtool/include/objtool/elf.h
+++ b/tools/objtool/include/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 {
--
2.29.2
next prev parent reply other threads:[~2021-01-21 21:36 UTC|newest]
Thread overview: 31+ messages / expand[flat|nested] mbox.gz Atom feed top
2021-01-21 21:29 [PATCH v2 00/20] objtool: vmlinux.o and CLANG LTO support Josh Poimboeuf
2021-01-21 21:29 ` [PATCH v2 01/20] objtool: Fix error handling for STD/CLD warnings Josh Poimboeuf
2021-01-21 21:29 ` [PATCH v2 02/20] objtool: Fix retpoline detection in asm code Josh Poimboeuf
2021-01-21 21:29 ` [PATCH v2 03/20] objtool: Fix ".cold" section suffix check for newer versions of GCC Josh Poimboeuf
2021-01-21 21:29 ` [PATCH v2 04/20] objtool: Support retpoline jump detection for vmlinux.o Josh Poimboeuf
2021-01-21 21:29 ` [PATCH v2 05/20] x86/ftrace: Add UNWIND_HINT_FUNC annotation for ftrace_stub Josh Poimboeuf
2021-01-21 21:29 ` [PATCH v2 06/20] objtool: Assume only ELF functions do sibling calls Josh Poimboeuf
2021-01-21 21:29 ` [PATCH v2 07/20] objtool: Add asm version of STACK_FRAME_NON_STANDARD Josh Poimboeuf
2021-01-21 21:29 ` [PATCH v2 08/20] objtool: Combine UNWIND_HINT_RET_OFFSET and UNWIND_HINT_FUNC Josh Poimboeuf
2021-01-21 21:29 ` [PATCH v2 09/20] objtool: Add xen_start_kernel() to noreturn list Josh Poimboeuf
2021-01-21 21:29 ` [PATCH v2 10/20] objtool: Move unsuffixed symbol conversion to a helper function Josh Poimboeuf
2021-01-21 21:29 ` Josh Poimboeuf [this message]
2021-01-21 21:29 ` [PATCH v2 12/20] x86/xen: Support objtool validation in xen-asm.S Josh Poimboeuf
2021-01-21 21:29 ` [PATCH v2 13/20] x86/xen: Support objtool vmlinux.o validation in xen-head.S Josh Poimboeuf
2021-01-21 21:29 ` [PATCH v2 14/20] x86/xen/pvh: Annotate indirect branch as safe Josh Poimboeuf
2021-01-22 5:17 ` Jürgen Groß
2021-01-21 21:29 ` [PATCH v2 15/20] x86/ftrace: Support objtool vmlinux.o validation in ftrace_64.S Josh Poimboeuf
2021-01-21 21:29 ` [PATCH v2 16/20] x86/acpi: Annotate indirect branch as safe Josh Poimboeuf
2021-01-21 21:29 ` [PATCH v2 17/20] x86/acpi: Support objtool validation in wakeup_64.S Josh Poimboeuf
2021-01-21 21:29 ` [PATCH v2 18/20] x86/power: Annotate indirect branches as safe Josh Poimboeuf
2021-01-21 21:29 ` [PATCH v2 19/20] x86/power: Move restore_registers() to top of the file Josh Poimboeuf
2021-01-21 21:29 ` [PATCH v2 20/20] x86/power: Support objtool validation in hibernate_asm_64.S Josh Poimboeuf
2021-01-21 22:38 ` [PATCH v2 00/20] objtool: vmlinux.o and CLANG LTO support Sedat Dilek
2021-01-22 15:41 ` Josh Poimboeuf
2021-01-22 21:17 ` Sami Tolvanen
2021-01-23 1:32 ` Nick Desaulniers
2021-01-23 2:26 ` Josh Poimboeuf
2021-01-23 2:31 ` Sedat Dilek
2021-01-23 2:46 ` Josh Poimboeuf
2021-01-23 2:50 ` Sedat Dilek
2021-01-25 22:43 ` Sami Tolvanen
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