Use ud1 as the guard instruction for the restartable sequence abort handler. Its benefit compared to nopl is to trap execution if the program ends up trying to execute it by mistake, which makes debugging easier.

The 4-byte signature per se is unchanged (it is the instruction operand). Only the opcode is changed from nopl to ud1.

Signed-off-by: Mathieu Desnoyers mathieu.desnoyers@efficios.com Suggested-by: Peter Zijlstra peterz@infradead.org CC: Peter Zijlstra peterz@infradead.org CC: Thomas Gleixner tglx@linutronix.de CC: Joel Fernandes joelaf@google.com CC: Catalin Marinas catalin.marinas@arm.com CC: Dave Watson davejwatson@fb.com CC: Will Deacon will.deacon@arm.com CC: Shuah Khan shuah@kernel.org CC: Andi Kleen andi@firstfloor.org CC: linux-kselftest@vger.kernel.org CC: "H . Peter Anvin" hpa@zytor.com CC: Chris Lameter cl@linux.com CC: Russell King linux@arm.linux.org.uk CC: Michael Kerrisk mtk.manpages@gmail.com CC: "Paul E . McKenney" paulmck@linux.vnet.ibm.com CC: Paul Turner pjt@google.com CC: Boqun Feng boqun.feng@gmail.com CC: Josh Triplett josh@joshtriplett.org CC: Steven Rostedt rostedt@goodmis.org CC: Ben Maurer bmaurer@fb.com CC: linux-api@vger.kernel.org CC: Andy Lutomirski luto@amacapital.net CC: Andrew Morton akpm@linux-foundation.org CC: Linus Torvalds torvalds@linux-foundation.org --- tools/testing/selftests/rseq/rseq-x86.h | 15 +++++++++++---- 1 file changed, 11 insertions(+), 4 deletions(-)

diff --git a/tools/testing/selftests/rseq/rseq-x86.h b/tools/testing/selftests/rseq/rseq-x86.h index 03095236f6fa..b2da6004fe30 100644 --- a/tools/testing/selftests/rseq/rseq-x86.h +++ b/tools/testing/selftests/rseq/rseq-x86.h @@ -7,6 +7,13 @@

#include <stdint.h>

+/* + * RSEQ_SIG is used with the following reserved undefined instructions, which + * trap in user-space: + * + * x86-32: 0f b9 3d 53 30 05 53 ud1 0x53053053,%edi + * x86-64: 0f b9 3d 53 30 05 53 ud1 0x53053053(%rip),%edi + */ #define RSEQ_SIG 0x53053053

/* @@ -88,8 +95,8 @@ do { \

#define RSEQ_ASM_DEFINE_ABORT(label, teardown, abort_label) \ ".pushsection __rseq_failure, "ax"\n\t" \ - /* Disassembler-friendly signature: nopl <sig>(%rip). */\ - ".byte 0x0f, 0x1f, 0x05\n\t" \ + /* Disassembler-friendly signature: ud1 <sig>(%rip),%edi. */ \ + ".byte 0x0f, 0xb9, 0x3d\n\t" \ ".long " __rseq_str(RSEQ_SIG) "\n\t" \ __rseq_str(label) ":\n\t" \ teardown \ @@ -609,8 +616,8 @@ do { \

#define RSEQ_ASM_DEFINE_ABORT(label, teardown, abort_label) \ ".pushsection __rseq_failure, "ax"\n\t" \ - /* Disassembler-friendly signature: nopl <sig>. */ \ - ".byte 0x0f, 0x1f, 0x05\n\t" \ + /* Disassembler-friendly signature: ud1 <sig>,%edi. */ \ + ".byte 0x0f, 0xb9, 0x3d\n\t" \ ".long " __rseq_str(RSEQ_SIG) "\n\t" \ __rseq_str(label) ":\n\t" \ teardown \