linux-kernel - Re: [PATCH v4 0/7] ptrace: introduce PTRACE_SET_SYSCALL

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Message-ID: <20250204151420.GA30282@strace.io>
Date: Tue, 4 Feb 2025 17:14:20 +0200
From: "Dmitry V. Levin" <ldv@...ace.io>
To: Alexander Gordeev <agordeev@...ux.ibm.com>
Cc: Andrew Morton <akpm@...ux-foundation.org>,
	Oleg Nesterov <oleg@...hat.com>, Shuah Khan <shuah@...nel.org>,
	Alexey Gladkov <legion@...nel.org>,
	Eugene Syromyatnikov <evgsyr@...il.com>,
	Mike Frysinger <vapier@...too.org>,
	Renzo Davoli <renzo@...unibo.it>,
	Davide Berardi <berardi.dav@...il.com>,
	Heiko Carstens <hca@...ux.ibm.com>,
	Vasily Gorbik <gor@...ux.ibm.com>,
	Christian Borntraeger <borntraeger@...ux.ibm.com>,
	Sven Schnelle <svens@...ux.ibm.com>, strace-devel@...ts.strace.io,
	linux-s390@...r.kernel.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCH v4 0/7] ptrace: introduce PTRACE_SET_SYSCALL_INFO API

On Mon, Feb 03, 2025 at 12:35:42PM +0200, Dmitry V. Levin wrote:
> On Mon, Feb 03, 2025 at 10:29:37AM +0100, Alexander Gordeev wrote:
> > On Mon, Feb 03, 2025 at 08:58:49AM +0200, Dmitry V. Levin wrote:
> > 
> > Hi Dmitry,
> > 
> > > PTRACE_SET_SYSCALL_INFO is a generic ptrace API that complements
> > > PTRACE_GET_SYSCALL_INFO by letting the ptracer modify details of
> > > system calls the tracee is blocked in.
> > ...
> > 
> > FWIW, I am getting these on s390:
> > 
> > # ./tools/testing/selftests/ptrace/set_syscall_info 
> > TAP version 13
> > 1..1
> > # Starting 1 tests from 1 test cases.
> > #  RUN           global.set_syscall_info ...
> > # set_syscall_info.c:87:set_syscall_info:Expected exp_entry->nr (-1) == info->entry.nr (65535)
> > # set_syscall_info.c:88:set_syscall_info:wait #3: PTRACE_GET_SYSCALL_INFO #2: syscall nr mismatch
> > # set_syscall_info: Test terminated by assertion
> > #          FAIL  global.set_syscall_info
> > not ok 1 global.set_syscall_info
> > # FAILED: 0 / 1 tests passed.
> > # Totals: pass:0 fail:1 xfail:0 xpass:0 skip:0 error:0
> > 
> > I remember one of the earlier versions (v1 or v2) was working for me.
> > 
> > Thanks!
> 
> In v3, this test was extended to check whether PTRACE_GET_SYSCALL_INFO
> called immediately after PTRACE_SET_SYSCALL_INFO returns the same syscall
> number, and on s390 it apparently doesn't, thanks to its implementation
> of syscall_get_nr() that returns 0xffff in this case.
> 
> To workaround this, we could either change syscall_get_nr() to return -1
> in this case, or add an #ifdef __s390x__ exception to the test.
> 
> What would you prefer?

OK, I'm going to apply the following s390 workaround to the test:

diff --git a/tools/testing/selftests/ptrace/set_syscall_info.c b/tools/testing/selftests/ptrace/set_syscall_info.c
index 0ec69401c008..4198248ef874 100644
--- a/tools/testing/selftests/ptrace/set_syscall_info.c
+++ b/tools/testing/selftests/ptrace/set_syscall_info.c
@@ -71,6 +71,11 @@ check_psi_entry(struct __test_metadata *_metadata,
 		const char *text)
 {
 	unsigned int i;
+	int exp_nr = exp_entry->nr;
+#if defined __s390__ || defined __s390x__
+	/* s390 is the only architecture that has 16-bit syscall numbers */
+	exp_nr &= 0xffff;
+#endif
 
 	ASSERT_EQ(PTRACE_SYSCALL_INFO_ENTRY, info->op) {
 		LOG_KILL_TRACEE("%s: entry stop mismatch", text);
@@ -84,7 +89,7 @@ check_psi_entry(struct __test_metadata *_metadata,
 	ASSERT_TRUE(info->stack_pointer) {
 		LOG_KILL_TRACEE("%s: entry stop mismatch", text);
 	}
-	ASSERT_EQ(exp_entry->nr, info->entry.nr) {
+	ASSERT_EQ(exp_nr, info->entry.nr) {
 		LOG_KILL_TRACEE("%s: syscall nr mismatch", text);
 	}
 	for (i = 0; i < ARRAY_SIZE(exp_entry->args); ++i) {

-- 
ldv