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x86/unwind/orc: Add ELF section with ORC version identifier

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Commits ffb1b4a410 ("x86/unwind/orc: Add 'signal' field to ORC
metadata") and fb799447ae ("x86,objtool: Split UNWIND_HINT_EMPTY in
two") changed the ORC format. Although ORC is internal to the kernel,
it's the only way for external tools to get reliable kernel stack traces
on x86-64. In particular, the drgn debugger [1] uses ORC for stack
unwinding, and these format changes broke it [2]. As the drgn
maintainer, I don't care how often or how much the kernel changes the
ORC format as long as I have a way to detect the change.

It suffices to store a version identifier in the vmlinux and kernel
module ELF files (to use when parsing ORC sections from ELF), and in
kernel memory (to use when parsing ORC from a core dump+symbol table).
Rather than hard-coding a version number that needs to be manually
bumped, Peterz suggested hashing the definitions from orc_types.h. If
there is a format change that isn't caught by this, the hashing script
can be updated.

This patch adds an .orc_header allocated ELF section containing the
20-byte hash to vmlinux and kernel modules, along with the corresponding
__start_orc_header and __stop_orc_header symbols in vmlinux.

1: https://github.com/osandov/drgn
2: https://github.com/osandov/drgn/issues/303

Fixes: ffb1b4a410 ("x86/unwind/orc: Add 'signal' field to ORC metadata")
Fixes: fb799447ae ("x86,objtool: Split UNWIND_HINT_EMPTY in two")
Signed-off-by: Omar Sandoval <osandov@fb.com>
Signed-off-by: Peter Zijlstra (Intel) <peterz@infradead.org>
Acked-by: Josh Poimboeuf <jpoimboe@kernel.org>
Link: https://lkml.kernel.org/r/aef9c8dc43915b886a8c48509a12ec1b006ca1ca.1686690801.git.osandov@osandov.com
This commit is contained in:
Omar Sandoval 2023-06-13 14:14:56 -07:00 committed by Peter Zijlstra
parent 858fd168a9
commit b9f174c811
7 changed files with 59 additions and 0 deletions
Show Stats Download Patch File Download Diff File Expand all files Collapse all files

12
arch/x86/Makefile
View File

@ -305,6 +305,18 @@ ifeq ($(RETPOLINE_CFLAGS),)
endif
endif
ifdef CONFIG_UNWINDER_ORC
orc_hash_h := arch/$(SRCARCH)/include/generated/asm/orc_hash.h
orc_hash_sh := $(srctree)/scripts/orc_hash.sh
targets += $(orc_hash_h)
quiet_cmd_orc_hash = GEN $@
cmd_orc_hash = mkdir -p $(dir $@); \
$(CONFIG_SHELL) $(orc_hash_sh) < $< > $@
$(orc_hash_h): $(srctree)/arch/x86/include/asm/orc_types.h $(orc_hash_sh) FORCE
$(call if_changed,orc_hash)
archprepare: $(orc_hash_h)
endif
archclean:
$(Q)rm -rf $(objtree)/arch/i386
$(Q)rm -rf $(objtree)/arch/x86_64

1
arch/x86/include/asm/Kbuild
View File

@ -1,6 +1,7 @@
# SPDX-License-Identifier: GPL-2.0
generated-y += orc_hash.h
generated-y += syscalls_32.h
generated-y += syscalls_64.h
generated-y += syscalls_x32.h

19
arch/x86/include/asm/orc_header.h Normal file
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@ -0,0 +1,19 @@
/* SPDX-License-Identifier: GPL-2.0-or-later */
/* Copyright (c) Meta Platforms, Inc. and affiliates. */
#ifndef _ORC_HEADER_H
#define _ORC_HEADER_H
#include <linux/types.h>
#include <linux/compiler.h>
#include <asm/orc_hash.h>
/*
* The header is currently a 20-byte hash of the ORC entry definition; see
* scripts/orc_hash.sh.
*/
#define ORC_HEADER \
__used __section(".orc_header") __aligned(4) \
static const u8 orc_header[] = { ORC_HASH }
#endif /* _ORC_HEADER_H */

3
arch/x86/kernel/unwind_orc.c
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@ -7,6 +7,9 @@
#include <asm/unwind.h>
#include <asm/orc_types.h>
#include <asm/orc_lookup.h>
#include <asm/orc_header.h>
ORC_HEADER;
#define orc_warn(fmt, ...) \
printk_deferred_once(KERN_WARNING "WARNING: " fmt, ##__VA_ARGS__)

3
include/asm-generic/vmlinux.lds.h
View File

@ -839,6 +839,9 @@
#ifdef CONFIG_UNWINDER_ORC
#define ORC_UNWIND_TABLE \
.orc_header : AT(ADDR(.orc_header) - LOAD_OFFSET) { \
BOUNDED_SECTION_BY(.orc_header, _orc_header) \
} \
. = ALIGN(4); \
.orc_unwind_ip : AT(ADDR(.orc_unwind_ip) - LOAD_OFFSET) { \
BOUNDED_SECTION_BY(.orc_unwind_ip, _orc_unwind_ip) \

5
scripts/mod/modpost.c
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@ -1979,6 +1979,11 @@ static void add_header(struct buffer *b, struct module *mod)
buf_printf(b, "#include <linux/vermagic.h>\n");
buf_printf(b, "#include <linux/compiler.h>\n");
buf_printf(b, "\n");
buf_printf(b, "#ifdef CONFIG_UNWINDER_ORC\n");
buf_printf(b, "#include <asm/orc_header.h>\n");
buf_printf(b, "ORC_HEADER;\n");
buf_printf(b, "#endif\n");
buf_printf(b, "\n");
buf_printf(b, "BUILD_SALT;\n");
buf_printf(b, "BUILD_LTO_INFO;\n");
buf_printf(b, "\n");

16
scripts/orc_hash.sh Normal file
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@ -0,0 +1,16 @@
#!/bin/sh
# SPDX-License-Identifier: GPL-2.0-or-later
# Copyright (c) Meta Platforms, Inc. and affiliates.
set -e
printf '%s' '#define ORC_HASH '
awk '
/^#define ORC_(REG|TYPE)_/ { print }
/^struct orc_entry {$/ { p=1 }
p { print }
/^}/ { p=0 }' |
sha1sum |
cut -d " " -f 1 |
sed 's/\([0-9a-f]\{2\}\)/0x\1,/g'