rseq/selftests: x86: use ud1 instruction as RSEQ_SIG opcode

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>
Signed-off-by: Shuah Khan <skhan@linuxfoundation.org>

diff --git a/tools/testing/selftests/rseq/rseq-x86.h b/tools/testing/selftests/rseq/rseq-x86.h
index 03095236f6fa1b14f1e1a9637793023ddc3a7f3f..b2da6004fe307931a500d0b50eba52cb46a06645 100644 (file)
--- 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                                                \