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| author | Josh Poimboeuf <jpoimboe@kernel.org> | 2023-04-07 17:16:41 -0700 |
|---|---|---|
| committer | Peter Zijlstra <peterz@infradead.org> | 2023-08-17 17:07:09 +0200 |
| commit | c6cfcbd8ca43766851a8c952e3b570727147020f (patch) | |
| tree | f67a704f7078b00d4f6124cee2c455cbaefaf8d8 /arch/x86/kernel/ibt_selftest.S | |
| parent | c6b53dcec07c842af75123d9b29684bdbd36a407 (diff) | |
| download | lwn-c6cfcbd8ca43766851a8c952e3b570727147020f.tar.gz lwn-c6cfcbd8ca43766851a8c952e3b570727147020f.zip | |
x86/ibt: Convert IBT selftest to asm
The following warning is reported when frame pointers and kernel IBT are
enabled:
vmlinux.o: warning: objtool: ibt_selftest+0x11: sibling call from callable instruction with modified stack frame
The problem is that objtool interprets the indirect branch in
ibt_selftest() as a sibling call, and GCC inserts a (partial) frame
pointer prologue before it:
0000 000000000003f550 <ibt_selftest>:
0000 3f550: f3 0f 1e fa endbr64
0004 3f554: e8 00 00 00 00 call 3f559 <ibt_selftest+0x9> 3f555: R_X86_64_PLT32 __fentry__-0x4
0009 3f559: 55 push %rbp
000a 3f55a: 48 8d 05 02 00 00 00 lea 0x2(%rip),%rax # 3f563 <ibt_selftest_ip>
0011 3f561: ff e0 jmp *%rax
Note the inline asm is missing ASM_CALL_CONSTRAINT, so the 'push %rbp'
happens before the indirect branch and the 'mov %rsp, %rbp' happens
afterwards.
Simplify the generated code and make it easier to understand for both
tools and humans by moving the selftest to proper asm.
Signed-off-by: Josh Poimboeuf <jpoimboe@kernel.org>
Signed-off-by: Peter Zijlstra (Intel) <peterz@infradead.org>
Link: https://lkml.kernel.org/r/99a7e16b97bda97bf0a04aa141d6241cd8a839a2.1680912949.git.jpoimboe@kernel.org
Diffstat (limited to 'arch/x86/kernel/ibt_selftest.S')
| -rw-r--r-- | arch/x86/kernel/ibt_selftest.S | 17 |
1 files changed, 17 insertions, 0 deletions
diff --git a/arch/x86/kernel/ibt_selftest.S b/arch/x86/kernel/ibt_selftest.S new file mode 100644 index 000000000000..c43c4ed28a9c --- /dev/null +++ b/arch/x86/kernel/ibt_selftest.S @@ -0,0 +1,17 @@ +/* SPDX-License-Identifier: GPL-2.0 */ +#include <linux/linkage.h> +#include <linux/objtool.h> +#include <asm/nospec-branch.h> + +SYM_CODE_START(ibt_selftest_noendbr) + ANNOTATE_NOENDBR + UNWIND_HINT_FUNC + /* #CP handler sets %ax to 0 */ + RET +SYM_CODE_END(ibt_selftest_noendbr) + +SYM_FUNC_START(ibt_selftest) + lea ibt_selftest_noendbr(%rip), %rax + ANNOTATE_RETPOLINE_SAFE + jmp *%rax +SYM_FUNC_END(ibt_selftest) |